Java Basics A Simple Hit the Zombies Game

Transcription

1 Lecture #3 Introduction Java Basics A Simple Hit the Zombies Game The previous lecture provided a guided tour to explore the basics of Android Studio and how to use it to create a project to build an Android game application. In this lecture, students will explore how Java programming skills apply to the making of Android games. In an Android Studio project, both the activity_main.xml and MainActivity.java files are the two core files for developers to work on. In the nutshell, the activity_main.xml file is used to define the appearance of all user interfaces (UIs), while the MainActivity.java file contains Java code to drive the application and control the behaviors of the application. The following figure illustrates the relationship. Android Project XML Java The intersection of XML and Java parts of the project indicates that programmers can write Java code to dynamically change appearances of the application. The following demonstrates how to use Java code to change the background color of a Button control with its identifier being button1. button1.setbackgroundcolor(color.white); In this lecture, students will work on five learning activities to develop a game named Hit the Zombies. Java Basics for Android As a specialized kind of Java application, an Android Java application can be described as a collection of objects defined by a Java class in order to invoke methods and implement properties. The term class is an official term used by the object-oriented programming to describe a logical container defined by the programmers for member definitions. The term members of a given class are typically made up of methods and properties. The following are the basic terms students should be familiar with in order to understand how Java coding applies to Android programming. Object Objects are identifiable items, such as a book, a button, a sprite, or a sound. An object has states (or appearance) and behaviors. For example, a game sprite has states including color, name, file size as well as behaviors like moving around the screen, changing its size, and fighting against an enemy. An object is also described as an instance of a class. The action of creating an instance is known as instantiation. class properties methods object 1 object 2 object n Class A class is a logical container for defining methods and properties. A class can also be defined as a template (or a blue print) that describes the behaviors and states for objects of its type to use. 69

2 Methods - A method is basically a code block that defines of a specific behavior. A class can contain many methods. For example, how an UFO object can fly from the ground to the sky is typically defined in a method. Properties (class variables) A property of a class is a variable that indicates one specific state of an object. For example, a variable named bgcolor is used to indicate the background color of an object. Package. A Java package is a group of similar types of classes, interfaces and subpackages. An Android project may consist of two or more individual classes. A package thus packs these individual classes as a single unit. In a package, all classes are peers to one another. A significant benefit of package is for members of these classes to easily access members of other peer classes. Programmers also typically use packages to organize classes belonging to the same category or providing similar functionality. In an Android Java program, a package can also provide a unique namespace for the data types it contains. If a package becomes a library, programmers can use the import directive to include classes and/or interfaces contained in that package by qualifying their names. In terms of programming, a library is a collection of pre-built resources for quickly developing new software. The terms, qualify a class, means to specify the full hierarchy (or file structure). In Android, a class has a hierarchy that starts with a namespace name, followed by a period (.), a package name, another period (.), and then the class name. The following demonstrates how to properly import a class (the TextView class) using its qualified name, which also depicts the file structure. The structure is: TextView is under widget, and widget is a child of android. import android.widget.textview; An Android project often requires programmers to import several resources. For example, every project must make a reference to the android.app.activity class to create a default window. Therefore, the following importing is required. import android.app.activity; Every Android application must have at least one class of the android.app.activity type; therefore, the Android Studio automatically declares a MainActivity class in every Android project, as shown below. This MainActivity class extends the android.app.activity class, so it is a derived (or subclass) of the android.app.activity class. In Java, extends is the keyword used to inherit members of a base (or superclass) class. public class MainActivity extends Activity By the way, Google now encourages to replace the android.app.activity class with the android.support.v7.app.appcompatactivity class. According to Google, the new AppCompactActivity is fully compatible to the android.app.activity class with additional supports on UIs like ActionBar. import android.support.v7.app.appcompatactivity; Throughout this semester, most Android coding project will start with the modification of the following MainActivity class to handle the default activity. Coding an activity is the writing of a Java code that supports a screen or UI. The MainActivity class in every Android application is the entry point of the application. The term entry point implies that it is what the Java virtual machine is looking for to read and start the application when the application is launched. public class MainActivity extends AppCompatActivity 70

3 In terms of Android, an activity is anything a user can interact with the application. The android.app.activity class is the base class (or superclass) provided by the Android API as toolkit to for Android programmers to create a container (known as a window ) to host all other user interfaces (UIs), such as Button and TextView controls. In the following figure, the MainActivity creates the default activity which has one TextView and one Button control in it to interact with the user. MainActivity textview 1 button1 This default activity is the foundation for building the default user interface (UI), known as a View which is created by the setcontentview(view) method. A View is a rectangular area on the screen that is responsible for drawing and event handling. Every Android project automatically contains a default View defined in the activity_main.xml, as demonstrated below. protected void oncreate(bundle savedinstancestate) super.oncreate(savedinstancestate); setcontentview(r.layout.activity_main); A properly written Java code can be used to create custom-made View. The following is a sample Android Java code that create a TextView control as the View. Inside the oncreate() method, the instructor purposely ignores the default View by commenting out the setcontentview(r.layout.activity_main); statement. In Java, the term comment out a line of statement means to put two slashes (//) at the beginning of a line of statement to force the compiler to ignore that particular line. The instructor, then, manually defines a TextView (which is a kind of View ) as the replacement of the default View. A TextView is also a kind of user interface provided by Android to display text (or message) to the user and optionally allows users to edit its caption. package my.labn_m; import android.app.activity; import android.os.bundle; import android.widget.textview; public class MainActivity extends Activity int size; // property private int resize() //method size = 6; return public void oncreate(bundle savedinstancestate) super.oncreate(savedinstancestate); TextView textview1 = new TextView(this); // an instance textview1.settext(resize()+""); // define content setcontentview(textview1); // define what to display 71

4 By properly importing the class, as showing the following statement, the currently Android project will actually import source code from android.widget.textview which was provided by Android API; therefore, programmers no longer have to write code to define what a TextView is. It is necessary to note that the qualified name clearly instructs the compiler where to obtain the source code from the library. import android.widget.textview; The above statement, on the other hand, also officially introduce the TextView class to the current Android project; therefore, programmers can start to create an instance of the TextView class without the need to define what TextView class is. The following statement illustrates the instantiation, in which textview1 is the identifier of the object. The textview1 object is also an instance of the TextView class. TextView textview1 = new TextView(this); In terms of Object-Oriented programming, an instance is created by a constructor of the class. A constructor in Java is a block of code that is designed to be called for execution only when an instance of a class needs to be created. A constructor shares the identifier with the class, the only difference is that the constructor name is followed by a pair of parentheses while the class name is not. The new keyword is a Java operator that creates the object. During the instantiation, the new operator is followed by a call to a constructor, which creates the object textview1. Class Name Object Name Assignment keyword Constructor TextView textview1 = new TextView(this) Another purpose of the above sample code is to demonstrate how to create a property and a method as members of the MainActivity class. As shown below, it creates an integer variable named size as a property and an integer method named resize(). int size; // property private int resize() //method size = 6; return size; By the way, private is a Java keyword which declares a member s access as private. That is, the member is only visible and accessible within the class, not from any other class (including subclasses). In Java, the visibility of private members can extend to nested classes. In the following figure, class 3 is a nested class to class 1 while class 2 is a peer to class 1. Only class 1 and class 3 can access the resize() method of class 1. package 1 class 1 - private int resize() Class 2 Class 3 The resize() method is declared as a method of int type, which indicates that it must give back an integer to whatever part of the Java code (the calling party) that calls it for 72

5 execution. The return keyword is used to give back from a method when its execution is complete. When a return statement is reached in a method, the program passes a value to the code that invoked it. When declaring the type of a method, programmers must decide whether the method should give back a value. If the choice is not to return a value, the data type must be void. The following is a sample void method. It does not give back any value to its calling party. void showresult() textview1.settext("winning!"); The purpose of the following line is to call the resize() method to receive the value of the size variable passed by the return keyword. textview1.settext(resize()+""); Since textview1 is the object that will display the text on the screen, it should be associated with the settext() which is a method provided by Android API to set the text (or caption) for the TextView to display. The text is a specified string. Interestingly, according to the Android API, the settext() method only accepts a String value as parameter. settext(string) There is a data type conflict between the resize() method and the settext() method. The resize() method returns only int type of data, while the settext() method accepts only String type of value as parameter. In Java, any data type, when combined with a pair of double quotes ("") becomes a String type, as shown below. The plus sign (+), in this case, is the concatenation operator, not the arithmetic addition operator. The term concatenation literally means to merge two or more pieces of data together to form a new single String data. A pair of double quotes without any character in them indicates a blank character. Students will exercise this coding technique throughout the entire course. resize() + "" One simple way to distinguish what roles the plus sign (+) plays in a statement is to check the data type of its two operands. If both operands are numeric values, the plus sign (+) is the addition operator; otherwise, it is used as the concatenation operator. ( ) // addition (3.5 + "4.1242") // concatenation This section discussed the MainActivity class and how to use it to create class members, such as properties and methods to be used by other code segments. In the next several sections, students will review Java programming basics. Data Types and Variable Declaration A data type of a value in a programming language is an attribute that tells the computer what kind of data that value can be. For instance, number of persons in a group must be integers only because a person cannot be split in pieces (or avatars) to join different groups. Before a piece of data can be recognized and processed by a computer, the data must be officially introduced to the computer by a program. The process of introduction a data to the computer is known as declaration. The following depicts the syntax for declaring a variable. DataType VariableName; In programming, it is necessary to specify that number of persons can only be integers, as shown below. The keyword int indicates that it is a piece of data of int type (integer), while 73

6 numberofpersons is the identifier the instructor chose to describe the variable. The term variable refers to an area of physical memory that will be allocated by the operating system to hold the data. The identifier of the variable is the name that represent the allocated memory area for the sake of identification. int numberofpersons; The price of a product, as those in a U.S. retail store, are not always whole numbers, such as They have fractional parts. It is necessary to declare such data as float or double because they support fractional values. Technically speaking, the word double means twice the memory size of the float type. Currently, Java float type is a single-precision 32-bit floating-point type, while double is a double-precision 64-bit floating-point type. float price; Answers to a question like Are you a human? can only be either Yes or No (True or False), but not both. It is better to declare such kind of data as boolean, which is a data type that allows only two possible values: True or False. Some programming languages choose to use 1 and 0 to represent True and False. boolean answer; Most programming languages supports primary data types including integer, floating point unit number, character, string, and pointer. The Android API supports most of the standard Java primitive data types. The following table lists the most commonly used data types. Table: Android (Java) Primitive Data Types Type Contains Default Size Range int Signed integer 0 32 bits to float floating point bits ±1.4E-45 to ± E+38 double floating point bits ±4.9E-324 to ± E+308 String Combination of characters NULL - - char Unicode character \u bits \u0000 to \uffff byte Signed integer 0 8 bits -128 to 127 boolean true or false false 1 bit NA It is necessary to note that the Java String type is a special type of data designed to hold a combination of characters; however, the Java String type is a class and not a primitive data type. After declaring a variable, programmer can assign a value to the variable using the assignment operator (=). The following depicts the syntax. The equal sign (=), in this case, does not check if both side of party are equivalent to each other. Instead, it simply tells the computer value is the value of variablename. variablename = value; Programmers can choose to declare a variable in one statement, and then assign a value to it in another statement. In the following example, declaration and value assignment are two individual statements. Throughout this course, the instructor will demonstrate this technique to declare global variables. In computer programming, a global variable is the one that is meant to be accessible by any part of the program without restriction. A detailed discussion is available in the Scope and Access Control section. 74

7 String gametitle;... gametitle = "Zombie 3"; Often, programmers will choose to declare and assign an initial value in one single statement, as shown below. String gametitle = "Zombie 3"; The following statement declares and creates a variable named increment of float type, and then assign 0.05f as initial value. In Java, value of float type must end with a f or F suffix. float increment = 0.05f; The following is another example that declares and creates a variable of int type with an initial value of 26. int imgwidth = 26; The following is a simple program that demonstrates how to declare integer variables and assign their initial values. It is necessary to note that the settext(parameter) function only accept String values as its parameter. A parameter is a value in a method (or function) that is passed to the method for further processing. Both x and y are declared as variables of int type. Their values, after the addition operation (x+y), still produce a value of int. Programmers needs to convert the int type to String type in order for the settext() method to accept the value. In Java, anything that combines with an empty character ("") automatically becomes a String literal. A literal in Java is a value with specified data type. Package my.labn_m; // n and m are numbers import android.app.activity; import android.os.bundle; import android.widget.textview; public class MainActivity extends public void oncreate(bundle savedinstancestate) super.oncreate(savedinstancestate); TextView tv = new TextView(this); int x = 5; // declare and assign initial value int y = 7; tv.settext((x+y) + ""); // convert an integer to string setcontentview(tv); In the above code, (x+y) is an expression that describe how to operate on two values to produce a new one. The plus sign (+), in this case, is the addition operator. In programming, an expression is a well-constructed code unit consisting of variables, operators, and/or method invocations, and must be constructed according to the syntax of the language, in order to produce a single value. Operators Throughout this course, students will frequently use four categories of operators : arithmetic, increment/decrement, relational (comparison), and logical operators. 75

8 An arithmetic operator is a built-in program that takes two operands and performs a calculation on them, particularly in addition, subtraction, multiplication, division, and modulus calculation. Table: Java Arithmetic Operators Operator Symbol Example Result Addition Subtraction Multiplication * 5 * 3 15 Division / 5/3 1 Modulus % 5%3 2 It is necessary to note that the expression, (5/3), actually produces 1 as result in Java. This is because Java operates data based on the data type. Both 5 and 3 are int type (which indicates they must be integer), so the result of operation must return a value of the same data type. In programming, integer division produces an integer rather than rational result; it truncates to the decimal representation of the rational result. The expression, (5.0/3.0), will produce the expected rational result because both 5.0 and 3.0 are floating-point type of data. In programming, the percentage sign (%) has a different definition. It represents the modulus operator. The modulus operator (%) is also known as remainder operator because it returns the remainder of two numbers as the result of an integer division. For instance, 10 % 3 is 1 because 10 divided by 3 leaves a remainder of 1. Programmers often take advantages of the modulus operator to simplify a complicated situation. The following is an example that can form a good programming logic to determine if a given year is a leap year. If year % 4 = 0, then it's a leap year if a year % 100 and if year % 400 = 0, then it's a leap year if a year % 100 and if year % 400!= 0, then it's not a leap year else, it's not a leap year The following is a sample pseudocode written based on the above logic. if (((y % 4 == 0) && (y % 100!= 0)) (y % 400 == 0) y is a leap year else y is not a leap year The above pseudocode uses one of the rational operator, the equal to operator (==). Relational operators are operators that test or evaluate relation between two operands to return a Boolean result: True or False. They are often used in Java expressions to make basic decisions. Table: Relational Operators Operators Description Example Results == Equal to 3 == 3 true!= Not equal to 3!= 5 true > Greater than 3 > 5 false >= Greater than or equal to 3 >= 5 false < Less than 3 < 5 true <= Less than or equal to 3 <= 5 true 76

9 It is necessary to distinguish the equal to operator (==) with the assignment operator (=). In programming, it takes two consecutive equal signs (==) to denote the equal to operator. The assignment operator is the one that has only one equal sign (=). Increment (++) and decrement ( ) operators in Java programming are designed to add 1 to, or subtract 1 from its operand. They are used as a shortcut to modify the value stored in a variable and access that value. Table: Increment and Decrement Operators Operator Example Equivalence Description ++ x++ x = x + 1 Adds 1 to the current value of x. -- x-- x = x - 1 Subtract 1 from the current value of x. += x += 3 x = x + 3 Adds 3 to the current value of x. -= x -= 3 x = x - 3 Subtract 3 from the current value of x. *= x *= 3 x = x * 3 Multiply 3 with the current value of x. The addition assignment operator (+=) adds the value of an expression to the value of a variable and assigns the result to the variable. The subtraction assignment operator (-=) subtracts the value of an expression from the value of a variable and assigns the result to the variable. The multiplication assignment operator (*=) multiplies the value of a variable by the value of an expression and assigns the result to the variable. In the following example, the multiply assign operator (*=) combines multiplication with assignment operations, and force its left operand to multiply itself with 1.1. imageview1.getlayoutparams().width *= 1.1; imageview1.getlayoutparams().height *= 1.1; Logical operators are typically used with Boolean (logical) values to produce one Boolean value as result. Operator Description Example && AND x < 40 && y > 90 OR x < 0 x > width! NOT!x > 0 The logical AND operator (&&) performs a logical conjunction on two expressions. The operation returns true only if both operands are true; otherwise, it returns false. The logical OR operator ( ) performs a logical disjunction on two expressions. If either or both expressions evaluate to True, result is True. The logical NOT operator (!) performs logical negation on an expression. In the following example, the getlayoutparams() method will get the value of the width property from imageview1 and assigns that value to a variable imgwidth of int type. Then, the OR ( ) operator will evaluate a hybrid expression which consists of two individual expressions: imgwidth >= (w * 0.9) and imgwidth < 26. int imgwidth = imageview1.getlayoutparams().width;... (imgwidth >= (w * 0.9) imgwidth < 26) 77

10 In the following example, x is 5, so (x<=4) is False. However, the NOT (!) operator is used to check if the expression is Not False. Since the entire expression,!(x <=4), is actually not False, the result is True. int x = 5;...!(x <= 4) Array Game programming frequently use arrays to manipulate game data. An array is a collection of items that all have something in common. The commonality is what you need to use to group them in an array. By using an array variable, which store more than one possible value as element to a variable, you can avoid creating many variables for similar type of data. Each possible value of an array is known as an element. The sequence of an element is indicated by an index. The following illustrates the syntax: DateType[] arrayname; arrayname = new DataType[size] where, datatype is a keyword that actually represents a data type, such as int, float, or String; arrayname is the identifier given to the array; size is the total number of elements allowed; and new is the Java keyword that actually creates the array. The following declares an array of float type with an identifier (or name) body_weight. float[] body_weight; Declaration alone cannot create the array; the following uses the new keyword to actually create the array. It also specifies that the array can only host 5 elements. body_weight = new float[5]; The term size (or length ) refers to the total allowed number of elements of an array. If an array is said to have a size of 5, then it can only host 5 elements. The value of index typically starts at 0, not 1. Throughout this course, students will frequent declare, create, and populate arrays. For example, the following declares an array named x that will be used to store three zombies x- coordinates in a game. int[] x; After declaration, the following uses the new keyword to create the array that can host no more than 3 elements. x = new int[3]; To populate and array means to actually create elements of the array. The new keyword can build an abstract container for the array to host elements, but it does not create the elements. Programmer must use the following syntax to populate elements. arrayname[index] = value; The index of element are integers starting at 0 and ending at size-1. In the case of x array, the first element is x[0], the second is x[1], and the third is x[2]. The following illustrates how to populate these three elements. 78

11 Sprite Index x-coordinate Populating elements Zombie x[0] = 10; Zombie x[1] = 25; Zombie x[2] = 40; The following is the syntax for retrieving value from a populated element. arrayname[index] The following is an example that attempts to retrieve the value of x[0]. Parameter of the settext() method must be a String type, therefore, the instructor concatenate x[0] with a blank character. textview1.settext(x[0] + ""); A complete sample code is: package my.labn_m; // m and n are import android.app.activity; import android.os.bundle; import android.widget.textview; public class MainActivity extends public void oncreate(bundle savedinstancestate) super.oncreate(savedinstancestate); TextView textview1 = new TextView(this); int[] x = new int[3]; x[0] = 10; x[1] = 25; x[2] = 45; textview1.settext(x[1]+""); setcontentview(tv); If the size of an array is small, you can declare an array and its containing elements in a single line. This is a short-hand way to create an array. For example, double[] d = 3.1, 2.6, 7.5; The following is the short-hand way to create a String array. String[] arrayofstring = "A", "B", "C", "D"; You can create a jagged array in Android. For example, int[][] x = 3, 4, 5, 77, 50 ; A jagged array is an array whose elements are arrays. The elements of a jagged array can be of different dimensions and sizes. A jagged array is sometimes called an "array of arrays." The following examples show how to declare, initialize, and access jagged arrays. If you need to handle both x- and y-coordinates of three zombie sprites, you can declare a jagged array. For example, (10, 5), (25, 15), and (40, 35). int[][] zombie = new int[3][2]; 79

12 Or, simply zombie[0][0] = 10; zombie[0][1] = 5; zombie[1][0] = 25; zombie[1][1] = 15; zombie[2][0] = 40; zombie[2][1] = 35; int[][] zombie = 10, 5, 25, 15, 40, 35; The if Statements A decision structure is a fundamental control structure in game logics. The if..else statement is the most fundamental decision structure. The following illustrates the syntax, which includes optional else if segments. All the else if segments are on-demand segments, they are added only when they are deemed necessary. if (condition) // execute only when condition is true else if (condition2) // execute only when condition2 is true... else if (conditionn) // execute only when conditionn is true else // execute when all conditions are false To build an if structure, the if part is absolutely needed, in which the condition must be a Boolean expression that only produces one of the two possible values: True or False. In the following example, the expression, imgwidth < 26, is either True or False. Interestingly, the else can be omitted unless it is needed to make the decision-making process more complete. if (imgwidth < 26) imageview1.getlayoutparams().width = 26; imageview1.getlayoutparams().height = 31; The following is a complete code that illustrates how to use the if..else statement. The condition is defined by an expression, (3>5). When (3>5) is evaluated to be True, the message to display in a TextView is Correct! ; otherwise, it displays Incorrect!. package my.lab0_1; // m and n are import android.app.activity; import android.os.bundle; import android.widget.textview; public class MainActivity extends public void oncreate(bundle savedinstancestate) super.oncreate(savedinstancestate); TextView tv = new TextView(this); String msg=""; // blank if (3>5) msg = "Correct!"; 80

13 else msg = "Incorrect!"; tv.settext(msg); setcontentview(tv); The following is an example that use if..else if..else statement with String as a switch statement in Java example source code. If also demonstrates how to call a function (or method) that returns a value to its calling party (e.g.). Notice that the equals() method of java.lang.object acts the same as the == operator; that is, it tests for object identity rather than object equality. The implicit contract of the equals() method, however, is that it tests for equality rather than identity. package my.labm_n; // m and n are numbers import android.app.activity; import android.os.bundle; import android.widget.textview; public class MainActivity extends public void oncreate(bundle savedinstancestate) super.oncreate(savedinstancestate); TextView tv = new TextView(this); tv.settext(getlevel("a")); // call getlevel() function setcontentview(tv); private String[] arrayofstring = "A", "B", "C", "D"; public String getlevel(string level) String str = "You entered " + level + "\n"; if (arrayofstring[0].equals(level)) str += "Level A"; else if (arrayofstring[1].equals(level)) str += "Level B"; else if (arrayofstring[2].equals(level)) str += "Level C"; else if (arrayofstring[3].equals(level)) str += "Level D"; else str += Invalid request!!! ; return str; The above code uses a layered if statement. It also depicts that the pair of and is optional in Java coding. However, throughout this course, the instructor prefers using curly bracket to enclose code segments. if (condition1) else if (condition2) else if (condition3)... else Conditions in an if structure can be hybrid expressions. The following is a sample, excerpted from Learning Activity #2, that uses a hybrid expression. The imgwidth variable holds the value of the layout_width property of a given ImageView. The hybrid expression consists of two expressions: imgwidth >= (w * 0.9) and imgwidth < 26. These two 81

14 expressions are operands of an OR ( ) operator. By the way, the variable w in the following code holds the width of the device screen. if (imgwidth >= (w * 0.9) imgwidth < 26)... The switch..case Statement The switch..case statement is another decision structure. The switch Statement allows for any number of possible execution paths. An if..then..else statement can be used to make decisions based on ranges of values or conditions, whereas a switch statement can make decisions based only on a single integer or enumerated value. The syntax is: switch(position) case 0: statement; break; case 1: statement; break; case 2: statement; break;... case n: statement; break; default: The position of a switch can be int, short, char, and other primitive data types. The break statement after each case terminates the enclosing switch statement. The break statements are necessary because without them, case statements fall through; that is, a situation known as case hopping which means the control will flow sequentially through subsequent case statements without an explicit break. The optional default section is used to handle un-defined cases, which occurs when a value given to position that cannot be matched with all the defined cases. In this above, example, -1 is an un-defined case. By the way, the default case is always placed as the last case; therefore, whether or not to have a break statement to terminate its section is also optional. The following is a sample code, excerpted from Learning Activity #4, to randomly select an image file in the drawable subdirectory of R for the imageview1 to load. Random rnd = new Random(); int n = rnd.nextint(6);... int rid = 0; switch (n) case 0: rid = R.drawable.zombie1; break; case 1: rid = R.drawable.zombie2; break; case 2: rid = R.drawable.zombie3; break; case 3: rid = R.drawable.zombie4; break; case 4: rid = R.drawable.zombie5; break; case 5: rid = R.drawable.zombie6; break;... imageview1.setimageresource(rid); The following is an example that shows how a switch..case statement are used to determine key events. When the left arrow key ( ) is pressed, the Boolean variable handled is set to be true. When the right arrow key ( ) is pressed, handled is set to be false. When any other key is pressed, handled is also set to false. 82

15 @Override public boolean onkeydown(int keycode, KeyEvent event) super.onkeydown(keycode, event); boolean handled = true; // handle key presses switch (keycode) case KeyEvent.KEYCODE_DPAD_LEFT: handled = true; break; case KeyEvent.KEYCODE_DPAD_RIGHT: handled = false; break; default: handled = false; break; return handled By the way, in is used to mark methods that override a method declaration in a superclass. Compilers produce an error if a method annotated does not actually override a method in a superclass. Repetition structure The for statement provides a compact way to iterate over a range of values. Programmers often refer to it as the for loop because of the way in which it repeatedly loops until a particular condition is satisfied. The general form of the for statement can be expressed as follows: for (initialization; termination; increment) statement(s) When using this version of the for statement, keep in mind that: The initialization expression initializes the loop; it will only execute once at the moment when the looping begins. When the termination expression evaluates to False, the iteration (looping) terminates. The increment expression is invoked after each iteration. When the increment is based on a negative value, it is known as decrement. The following is a sample for loop. The variable i serves as a counter of iterations. The initial value of i is set to be 0. The termination expression is (i<9), which means the value of i must be less than 9. It is necessary to note that i is a variable of int type whose initial value is 0. Both the initiation and termination expressions collaboratively specify that the value of i can only be 0, 1, 2,, and 8 with an increment of 1. for (int i=0; i<9; i++) The following is another example of for loop. Its initial value of counter variable i is 5, terminal value is 50 because of the expression (i<=50), and its increment is 5. This for loop progresses in a skip counting mode from 5, 10, 15, to 45, 50. for (int i=5; i<=50; i+=5) The following demonstrates the use of decrement, and the decrement is -1. for (int i=12; i>3; i--) The following is the sample code that demonstrates how a for loop works. 83

16 package my.lab0_1; // m and n are import android.app.activity; import android.os.bundle; import android.widget.textview; public class MainActivity extends public void oncreate(bundle savedinstancestate) super.oncreate(savedinstancestate); TextView tv = new TextView(this); int[][] zombie = new int[3][2]; zombie[0][0] = 10; zombie[0][1] = 5; zombie[1][0] = 25; zombie[1][1] = 15; zombie[2][0] = 40; zombie[2][1] = 35; String str = ""; for (int i=0; i<3; i++) str += zombie[i][0]; tv.settext(str); setcontentview(tv); The while statement continually executes a block of statements while the termination expression is True. Its syntax can be expressed as: initiation while (termination) statement(s) increment The while statement evaluates expression, which must return a boolean value. If the expression evaluates to true, the while statement executes the statement(s) in the while block. The while statement continues testing the expression and executing its block until the expression evaluates to false. The following is a simple example, the counter variable i is set to start at 3, the termination expression (i<15) sets the last possible value to be 14, and the increment is 1. Consequently, the value of i can only be 3, 4, 5,, and 14. int i=3; while (i<15) // statements i++; The following is another example. Its first possible value is 0, the last possible value is 20 because (i<25), and the increment is 5. All the possible values of i are 0, 5, 10, 15, and 20. int i=0; 84

17 while (i<25) // statements i+=5; The following demonstrates how a while loop handles decrement. int i=9; while (i>=0) // statements i--; The following is the sample code that demonstrates how a while loop works. package my.labn_m; // m and n are import android.app.activity; import android.os.bundle; import android.widget.textview; public class MainActivity extends public void oncreate(bundle savedinstancestate) super.oncreate(savedinstancestate); TextView tv = new TextView(this); int[][] zombie = 10, 5, 25, 15, 40, 35; String str = ""; int i=0; while (i<3) str += zombie[i][0]; i++; tv.settext(str); setcontentview(tv); Pre-built Methods With Android Studio, application developers create new projects and modify the MainActivity.java files with custom-made Java code. These Java code usually utilize prebuilt methods provided by the Android SDk. The term built-in mean they are methods created by the programming team of the Android SDK for all other application developer to use. In the following sample statement, settext() is a method provided by the Android SDK. textview1.settext("zombie 3"); The findviewbyid() method is another frequently used pre-built method, which is provided by the Android SDK. ImageView imageview1 = (ImageView) findviewbyid(r.id.imageview1); The Android SDK contains many classes with each provide different sets of methods. A class is defined by a set of declaration statements and members, including properties, 85

18 methods, and constructor. Class properties in Java are typically variables. The term method is adapted by the object-oriented programming to describe a block of well-arranged statements to perform a special task. Constructors are special kind of methods that only create instances of the class. Throughout this course, students will use many pre-built methods to retrieve resources. The following example use the getlayoutparams() method to access properties of the LayoutParams object associated with a specified ImageView. The android.view.viewgroup.layoutparams class provides members to specify layout of a View. Both width and height are two parameters that specify how wide and how tall the view has to be. imageview1.getlayoutparams().width *= 1.1; imageview1.getlayoutparams().height *= 1.1; The multiply assign operator (*=) combines multiplication with assignment operations, and force its left operand to multiply itself with right operand. In the above example, both width and height parameters of the imageview1 are forced to enlarge by 1.1 fold. The above code can create a Zoom In visual effect of an image, while the following can create a Zoom Out visual effect. Learning Activity #1 will demonstration of such technique. imageview1.getlayoutparams().width *= 0.9; imageview1.getlayoutparams().height *= 0.9; According to Android SDK, the requestlayout() method must be called to re-initiate (or refresh) a layout, as shown below. This method is typically called by a view on itself when it believes that is can no longer fit within its current bounds. imageview1.requestlayout(); The following demonstrates how to set the Activity title by getting a string from the Resources object. It also demonstrates how to get an instance of Resources with Context.getResources() method. The getwindow() method retrieves the current Window for the activity (such as the MainActivity ). The gettext() method retrieves the caption (or value of the text property) of a resource. getwindow().settitle(getresources().gettext(r.string.main_title)); The following programmatically assigns an image from a drawable resource as background to the current screen. getwindow().setbackgrounddrawableresource(r.drawable.bg); In order to detect and respond to user activities (such as the onclick event), Androids SDK provide many listener methods that can detect the occurrence of an event. In terms of programming, an event is an action perform by a user, such as pressing a key, clicking a button, touch an object on the screen. In terms of Java programming, a listener is a mechanism (typically a method) provided by the Java language as a class (or interface) to detect whether or not a demanded event occurs. The following demonstrates how to create a View.OnClickListener object and assign it to the button by calling setonclicklistener(view.onclicklistener) in order to declare the event handler programmatically. Button button1 = (Button) findviewbyid(r.id.button_send); Button1.setOnClickListener(new View.OnClickListener() public void onclick(view v) // Do something in response to button click 86

19 ); When a player clicks the button1 control, the setonclicklistener() method will detect the event and immediately call the onclick() method to respond to the event. Programmers must override the onclick() method by adding Java code to specify the response actions. A later lecture will discuss about the concept of Java listener in details. User-defined functions The MainActivity.java file in essence is a Java class that is specially tailored to fit in the Android environment. Therefore, programmers can make add named blocks of statements to the MainActivity class as custom-made members. Interestingly, when the programmer has to organize a set of statement in a named block, the entire block is known as a user-defined function. However, it is probably appropriate to say that a user-defined function is a custom-made method of a Java class. Both method and user-defined functions must be called for execution. They are not executed automatically. A named block, in Java, must stick to the following syntax. The block of statements must be enclosed by and. datatype functionname() statements where, datatype can be any of the recognized data type such as int, float, char, and String as well as the void type; functionname is a unique identified given by the programmer as the name of the code block; and statements are lines of Java code that can perform a task. The following is a function named getimage() that will send a value of int to its calling party. In Java, the return keyword is used to return a value. int getimage(int n) int rid = 0;... return rid; It is necessary to note the void type. In Java, a function of void type is one that does not return anything to its calling party. The following is a sample void function, excerpted from Learning Activity #2. The resizeimage() function simply perform the designated task, but it does not return anything to its calling party. resizeimage(-0.1f); // call the function and pass a value void resizeimage(float increment) // function imageview1.getlayoutparams().height *= (1 + increment); imageview1.getlayoutparams().width *= (1 + increment); imageview1.requestlayout(); The content of the resizeimage() function (as demonstrated in Learning Activity #2) is also part of the content of button1 and button2 (Learning Activity #2) as shown below. Apparently, organizing repeating code as an individual function is an efficient way to make Java code reusable. 87

20 // Zoom in Button button1 = (Button) findviewbyid(r.id.button1); button1.setonclicklistener(new View.OnClickListener() public void onclick(view v) increment = 0.1f; imageview1.getlayoutparams().height *= (1 + increment); imageview1.getlayoutparams().width *= (1 + increment); imageview1.requestlayout(); ); // Zoom out Button button2 = (Button) findviewbyid(r.id.button2); button2.setonclicklistener(new View.OnClickListener() public void onclick(view v) increment = -0.1f; imageview1.getlayoutparams().height *= (1 + increment); imageview1.getlayoutparams().width *= (1 + increment); imageview1.requestlayout(); ); For API 17 and higher, programmer can call the Display.getRealSize() method to obtain the real size of the display. Interestingly, the actual size may be smaller than the physical size of the screen when the window manager is emulating a smaller display. The two variables of int type, w and h, are used to temporarily how the value of screen dimension. import android.view.display;... Display display = getwindowmanager().getdefaultdisplay(); Point size = new Point(); display.getrealsize(size); int w = size.x; int h = size.y; The instructor organizes the above code as a void type of user-defined function name showdisplaysize(). Therefore, whenever the application needs to re-obtain the screen dimension (after a rotation from Portrait to Landscape orientation), the values of w and h can be updated by calling the showdisplaysize() function. Learning Activity #2 demonstrates how the showdisplaysize() function works. int w, h;... void showdisplaysize() Display display = getwindowmanager().getdefaultdisplay(); Point size = new Point(); display.getrealsize(size); w = size.x; h = size.y; Prior to the API Level 17, programmers will have to use the following code snippet to obtain the actual screen width and height from an activity (such as the "MainActivity"). Display display = getwindowmanager().getdefaultdisplay(); Point size = new Point(); 88

21 display.getsize(size); int w = size.x; int h = size.y; Scope and Access Control In programming, scope of a variable or a method defines the accessibility of them. In other words, scope restricts where a variable or a method is accessible. public class MainActivity extends AppCompatActivity int cnt = 0; // a member of MainActivity class protected void oncreate(bundle savedinstancestate) int noofimages = 0; // a member of oncreate... noofimages = cnt; // access cnt void countzombies() cnt = query("android.view.imageview").count; The use of android.os.handler class to manipulate a Java Runnable object is a good example of scope. The following code, excerpted from Learning Activity #3, declares and instantiate a Handler object outside the Runnable object. Therefore, the run() method (which resides inside the Runnable object) can access the Handler object. A Java Runnable represent a task in Java which is executed by Thread. A Thread in Java is an independent flow of execution in a program that perform a specific task. Since a "thread" is independent, it can be started, paused, and stopped by the program it resides any time. Handler handler1 = new Handler();... Runnable runnable = new public void run()... handler1.postdelayed(this, 1000); ; handler1.postdelayed(runnable, 1000); A later lecture will discuss in details about the how to use Thread in Java. In this lecture, the above code is used to create a timer that sets a delay of 1000 milliseconds (which is 1 second) before the next execution. The above code, once launched, will also repeat the same task every 1 second. The instructor uses the above code to resize an image every second to create a visual effect that the image is moving towards the player. Learning Activity #3 will demonstrate how such visual effect works. References Review Question 1. Given the following statement, which is NOT correct? public class MainActivity extends AppCompatActivity A. "MainActivity" is a Java class that inherits "AppCompatActivity". 89

22 B. "AppCompatActivity" is a superclass. C. "MainActivity" class can use members of the "AppCompatActivity" class. D. The "AppCompatActivity" class can use members of the "MainActivity" class. 2. In which of the following, the word "size" is possibly the identifier of a method of a Java class? A. int size; B. int size() C. size = 100; D. return size; 3. Assuming "textview1" is a variable of the "TextView" type in Android Studio, which can display the correct result of an arithemetic expression (5-2) using the settext() method? A. textview1.settext(5-2); B. textview1.settext(5-2 + ""); C. textview1.settext((5-2) + ""); D. textview1.settext("(5-2)"); 4. What is the result of x after the following statements? A. 6 B. 5 C. 4 D. 3 C int x = 5; x--; 5. Given the following statement, which is the third element of "zombie" array? A. zombie[1] B. zombie[2] C. zombie[3] D. zombie[4] String[] zombie = new String[5]; 6. Which is not the correct way to declare a variable in Android Java programming? A. String size = "12"; B. int size; size = 12; C. int size = "12"; D. String size; size = "12"; 7. Given the following code, Android emulate should display. if (3>5) msg = "Correct!"; else msg = "Incorrect!"; A. Correct! B. Incorrect! C. Correct!Incorrect! D. Incorrect!Correct! 8. Given the following code, Android emulate should display. 90

23 if (3>5 3<5) msg = "Correct!"; else msg = "Incorrect!"; A. Correct! B. Incorrect! C. Correct!Incorrect! D. Incorrect!Correct! 9. Given the following code segment, in which condition will the "zombie4.png" file in the "res/drawable" folder be loaded? A. n = 2; B. n = 3; C. n = 4; D. n = 5; switch (n) case 0: rid = R.drawable.zombie1; break; case 1: rid = R.drawable.zombie2; break; case 2: rid = R.drawable.zombie3; break; case 3: rid = R.drawable.zombie4; break; case 4: rid = R.drawable.zombie5; break; case 5: rid = R.drawable.zombie6; break; 10. Given the followng code, zombie[1][0] is. A. 10 B. 5 C. 25 D. 15 int[][] zombie = 10, 5, 25, 15, 40, 35; 91

24 Lab #3 Java Basics Hitting Zombie Game Preparation #1: Download lab file 1. Create a temporary, C:\temp, if it does not exist. 2. Download the zombie.zip file to the C:\temp directory, and then extract all its content to the C:\temp directory. Learning Activity #1: Data type and basic operators 1. Launch the Android Studio (as you did in the previous labs). 2. In the tool bar, click File, and then New Project 3. In the Create New Project window, enter the followings. Then, click Next. Application name: Lab3_1 Company Domain: Misato Project location: X:\AndroidStudioProjects\Lab3_1 (where X is the drive name) 4. Click Next on the Target Android Devices window. 5. Select Empty Activity on the Add an Activity to Mobile window, and then click Next. 6. Click Finish on the Customize the Activity window. 7. Use Windows Explorer to copy only the zombie.png file to the X:\AndroidStudioProjects\Lab3_1\app\src\main\res\drawable directory ( X is the drive name). 8. Click the app folder to expand it. Click the java sub-folder to expand it. Click the project name to expand it. Finally, double click the MainActivity file to open it in the editor mode. 92

25 9. In the project panel, click the activity_main.xml tab once. Click the Design tab at the bottom of Component Tree to display the design view. Palette activity_main.xml tab design view Component Tree Desgin tab 10. In the Palette, drag down the veil. to 11. On the design view, right-click the TextView that displays Hello World!, select Delete from the menu as shown below to remove it. 12. On the Palette, click the Layouts category, and then drag one LinearLayout (vertical) to the Component Tree and place it under the ConstraintLayout. Make sure the LinearLayout (vertical) is a child of ConstraintLayout, as shown below. 93

26 13. Drag two LinearLayout (horizontal) to the Component Tree and place them under the LinearLayout (vertical), as shown below. 14. From the Palette, drag two Button controls to the Component Tree and place them under the first LinearLayout (horizontal), as shown below. Change their ID properties to button1 and button2. Change their text properties to Zoom In and Zoom Out. 15. On the Palette, click the Images category. Drag in an ImageView control to to the Component Tree and place it under the second LinearLayout (horizontal). The Resources window will pop up. 16. In the Resources window, select the zombie image and click OK. 17. Change the ID property of the ImageView control to imageview1. It is necessary to remember that values of ID (which is short for identifier ) is case-sensitive. 18. Click the activity_main.xml tab once, and then click the Text tab at the bottom of the editor window to change to the editing view. 94

27 19. In the activity_main.xml file, manually set the layout_height of the first LinearLayout (horizontal) to 60dp.... <LinearLayout android:layout_width="match_parent" android:layout_height="60dp" android:orientation="horizontal" tools:layout_editor_absolutex="8dp" tools:layout_editor_absolutey="8dp"> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_weight="1" android:text="zoom In" /> In the activity_main.xml file, manually change the layout_width property to 26dp and layout_height to 32dp. Make sure the activity_main.xml file reflects the changes. <ImageView android:layout_width="26dp" android:layout_height="32dp" android:layout_weight="1" /> 21. The layout should look similar to the following. 22. In the MainActivity.java file, change the Java code to the following. package misato.lab3_1; import android.support.v7.app.appcompatactivity; import android.os.bundle; import android.view.view; import android.widget.imageview; import android.widget.button; 95

28 public class MainActivity extends AppCompatActivity ImageView imageview1; // declare a variable of ImageView type float increment = 0.1f; // declare and create a float type of protected void oncreate(bundle savedinstancestate) super.oncreate(savedinstancestate); setcontentview(r.layout.activity_main); imageview1 = (ImageView) findviewbyid(r.id.imageview1); //instantiation // Zoom in Button button1 = (Button) findviewbyid(r.id.button1); button1.setonclicklistener(new View.OnClickListener() public void onclick(view v) increment = 0.1f; imageview1.getlayoutparams().height *= (1 + increment); imageview1.getlayoutparams().width *= (1 + increment); imageview1.requestlayout(); ); // Zoom out Button button2 = (Button) findviewbyid(r.id.button2); button2.setonclicklistener(new View.OnClickListener() public void onclick(view v) increment = -0.1f; imageview1.getlayoutparams().height *= (1 + increment); imageview1.getlayoutparams().width *= (1 + increment); imageview1.requestlayout(); ); 23. In the tool bar, click the Run ( ) button to test the application. Click Zoom In and Zoom Out buttons. A sample output looks: 24. Capture a screen shot(s) similar to the above, and paste it/them to the lab3.doc (or.docx) document. 25. Copy the app-debug.apk. file to a temporary directory and rename it to lab3_1.apk. Learning Activity #2: function 1. Create a new Android Stuio project with an Empty Activity named lab3_2 with the following specifications: Application name: Lab3_2 96

29 Company Domain: Misato Project location: X:\AndroidStudioProjects\Lab3_2 (where X is the drive name) 2. Use Windows Explorer to copy only the zombie.png file to the X:\AndroidStudioProjects\Lab3_2\app\src\main\res\drawable directory ( X is the drive name). 3. Repeat all steps of Learning Activity #1, except the Java code in the MainActivity.java file. Change the Java code in the MainActivity.java file to the following. package misato.lab3_2; import android.support.v7.app.appcompatactivity; import android.os.bundle; import android.view.view; import android.widget.imageview; import android.widget.button; public class MainActivity extends AppCompatActivity ImageView imageview1; float increment = protected void oncreate(bundle savedinstancestate) super.oncreate(savedinstancestate); setcontentview(r.layout.activity_main); imageview1 = (ImageView) findviewbyid(r.id.imageview1); // Zoom in Button button1 = (Button) findviewbyid(r.id.button1); button1.setonclicklistener(new View.OnClickListener() public void onclick(view v) resizeimage(0.1f); ); // Zoom out Button button2 = (Button) findviewbyid(r.id.button2); button2.setonclicklistener(new View.OnClickListener() public void onclick(view v) resizeimage(-0.1f); ); void resizeimage(float increment) imageview1.getlayoutparams().height *= (1 + increment); imageview1.getlayoutparams().width *= (1 + increment); imageview1.requestlayout(); 4. In the tool bar, click the Run ( ) button to test the application. Click Zoom In and Zoom Out buttons A sample output looks: 97

30 5. Capture a screen shot(s) similar to the above, and paste it/them to the lab3.doc (or.docx) document. 6. Copy the app-debug.apk. file to a temporary directory and rename it to lab3_2.apk. Learning Activity #3: if..else structure and automatically refreshing 1. Create a new Android Stuio project with an Empty Activity named lab3_3 with the following specifications: Application name: Lab3_3 Company Domain: Misato Project location: X:\AndroidStudioProjects\Lab3_3 (where X is the drive name) 2. Use Windows Explorer to copy only the zombie.png file to the X:\AndroidStudioProjects\Lab3_3\app\src\main\res\drawable directory ( X is the drive name). 3. Repeat all steps of Learning Activity #2, except the Java code in the MainActivity.java file. Change the Java code in the MainActivity.java file to the following. 4. In the MainActivity.java file, change the Java code to the following. package misato.lab3_3; import android.support.v7.app.appcompatactivity; import android.os.bundle; import android.view.view; import android.widget.imageview; import android.os.handler; import android.view.display; import android.graphics.point; public class MainActivity extends AppCompatActivity ImageView imageview1; float increment = 0.05f; int w = 0; int imgwidth = 26; Handler handler1 = new protected void oncreate(bundle savedinstancestate) super.oncreate(savedinstancestate); setcontentview(r.layout.activity_main); imageview1 = (ImageView) findviewbyid(r.id.imageview1); imageview1.setonclicklistener(new View.OnClickListener() public void onclick(view v) reset(); 98

31 ); showdisplaysize(); // get the width of the screen Runnable runnable = new public void run() imgwidth = imageview1.getlayoutparams().width; if (imgwidth >= (w * 0.9) imgwidth < 26) increment = increment * -1; if (imgwidth < 26) reset(); resizeimage(increment); handler1.postdelayed(this, 100); ; handler1.postdelayed(runnable, 100); void showdisplaysize() Display display = getwindowmanager().getdefaultdisplay(); Point size = new Point(); display.getsize(size); w = size.x; void resizeimage(float increment) imageview1.getlayoutparams().height *= (1 + increment); imageview1.getlayoutparams().width *= (1 + increment); imageview1.requestlayout(); void reset() imageview1.getlayoutparams().width = 26; imageview1.getlayoutparams().height = 31; 5. In the tool bar, click the Run ( ) button to test the application. The image enlarges and then shrinks automatically. A sample output looks: 99

32 6. Capture a screen shot(s) similar to the above, and paste it/them to the lab3.doc (or.docx) document. 7. Copy the app-debug.apk. file to a temporary directory and rename it to lab3_3.apk. Learning Activity #4: 1. Create a new Android Stuio project with an Empty Activity named lab3_4 with the following specifications: Application name: Lab3_4 Company Domain: Misato Project location: X:\AndroidStudioProjects\Lab3_4 (where X is the drive name) 2. Use Windows Explorer to copy zombie1.png, zombie2.png, zombie3.png, zombie4.png, zombie5.png, and zombie6.png files to the X:\AndroidStudioProjects\Lab3_4\app\src\main\res\drawable directory (where X is the drive name). 3. On the design view, right-click the TextView that displays Hello World!, select Delete from the menu as shown below to remove it. 4. On the Palette, click the Layouts category, and then drag one LinearLayout (vertical) to the Component Tree and place it under the ConstraintLayout. Make sure the LinearLayout (vertical) is a child of ConstraintLayout. 5. Drag two LinearLayout (horizontal) to the Component Tree and place them under the LinearLayout (vertical). 6. From the Palette, drag on TextView control to the Component Tree and place it under the first LinearLayout (horizontal). Change the ID property of the TextView to textview1. Change its text property to Hit Number:. 7. On the Palette, click the Images category. Drag in an ImageView control to to the Component Tree and place it under the second LinearLayout (horizontal). The Resources window will pop up. 8. In the Resources window, select the zombie1 image and click OK. 9. Change the ID property of the ImageView control to imageview1. It is necessary to remember that values of ID. 10. In the MainActivity.java file, change the Java code to the following. 100

33 package misato.lab3_4; import android.support.v7.app.appcompatactivity; import android.os.bundle; import android.view.view; import android.widget.imageview; import android.os.handler; import android.view.display; import android.graphics.point; import android.widget.textview;; public class MainActivity extends AppCompatActivity TextView textview1; ImageView imageview1; float increment = 0.05f; int w = 0; int imgwidth = 26; int n = 0; int hit = 0; Handler handler1 = new protected void oncreate(bundle savedinstancestate) super.oncreate(savedinstancestate); setcontentview(r.layout.activity_main); textview1 = (TextView) findviewbyid(r.id.textview1); imageview1 = (ImageView) findviewbyid(r.id.imageview1); imageview1.setonclicklistener(new View.OnClickListener() public void onclick(view v) hit++; // increment textview1.settext("hit Number: " + hit); reset(); ); imageview1.setimageresource(getimage(n)); showdisplaysize(); // get the width of the screen Runnable runnable = new public void run() imgwidth = imageview1.getlayoutparams().width; if (imgwidth >= (w * 0.9)) reset(); resizeimage(increment); handler1.postdelayed(this, 10); ; 101

34 handler1.postdelayed(runnable, 10); void showdisplaysize() Display display = getwindowmanager().getdefaultdisplay(); Point size = new Point(); display.getsize(size); w = size.x; void resizeimage(float increment) imageview1.getlayoutparams().height *= (1 + increment); imageview1.getlayoutparams().width *= (1 + increment); imageview1.requestlayout(); int getimage(int n) int rid = 0; switch (n) case 0: rid = R.drawable.zombie1; break; case 1: rid = R.drawable.zombie2; break; case 2: rid = R.drawable.zombie3; break; case 3: rid = R.drawable.zombie4; break; case 4: rid = R.drawable.zombie5; break; case 5: rid = R.drawable.zombie6; break; return rid; void reset() imageview1.getlayoutparams().width = 26; imageview1.getlayoutparams().height = 31; n = n + 1; imageview1.setimageresource(getimage(n%6)); 11. In the tool bar, click the Run ( ) button to test the application. Zombies will take turn to approach the player. The player needs to tap on the enlarging image to earn credits. A sample output looks: 12. Capture a screen shot(s) similar to the above, and paste it/them to the lab3.doc (or.docx) document. 102

35 13. Copy the app-debug.apk. file to a temporary directory and rename it to lab3_4.apk. Learning Activity #5: for loop and array 1. Create a new Android Stuio project with an Empty Activity named lab3_5 with the following specifications: Application name: Lab3_5 Company Domain: Misato Project location: X:\AndroidStudioProjects\Lab3_5 (where X is the drive name) 2. Use Windows Explorer to copy nozombie.png, zombie1.png, zombie2.png, zombie3.png, zombie4.png, zombie5.png, and zombie6.png files to the X:\AndroidStudioProjects\Lab3_5\app\src\main\res\drawable directory ( X is the drive name). 3. Remove the existing Hello World! TextView. 4. From the Palette, drag a TableLayout to the Component Tree and place it under the ConstraintLayout as a child. The TableLayout contains four TableRow. 5. In the Component Tree, click first TableRow and change its ID property to row1, as shown below. Click the second TableRow and change its ID property to row2. Change the rest to row3 and row4. 6. From the Palette, drag one TextView control to the Component Tree and place it under row1 (TableRow) as a child to row1. Change the ID propert to textview1. 7. Click the row2 (TableRow) to select it. Add three ImageView controls to the row2 (TableRow), as shown below. Set their default images to zombie1, zombie2, and zombie3. Set their ID properties to imageview1, imageview2, and imageview3. 103

36 8. The layout on the design view should now look similar to the following. 9. Click the row3 (TableRow) to select it. Add three ImageView controls to the row3 (TableRow), as shown below. Set their default images to zombie4, zombie5, and zombie6. Set their ID properties to imageview4, imageview5, and imageview Make sure to design view look similar to the following. 11. In the activity_main.xml file, add the following layout_marginbottom attribute to the textview1. <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="textview" android:layout_marginbottom="25px" /> 12. In the MainActivity.java file, change the Java code to the following. package misato.lab3_5; 104

37 import android.support.v7.app.appcompatactivity; import android.os.bundle; import android.view.view; import android.widget.textview; import android.widget.imageview; import android.os.handler; import java.util.random; public class MainActivity extends AppCompatActivity TextView textview1; // declare and create array of ImageView type ImageView[] img = new ImageView[6]; int imgvid; // temp id for ImageViews int hit, miss; int selected_img = 0; Random rnd = new Random(); Handler handler1 = new protected void oncreate(bundle savedinstancestate) super.oncreate(savedinstancestate); setcontentview(r.layout.activity_main); textview1 = (TextView) findviewbyid(r.id.textview1); //populate array elements img[0] = (ImageView) findviewbyid(r.id.imageview1); img[1] = (ImageView) findviewbyid(r.id.imageview2); img[2] = (ImageView) findviewbyid(r.id.imageview3); img[3] = (ImageView) findviewbyid(r.id.imageview4); img[4] = (ImageView) findviewbyid(r.id.imageview5); img[5] = (ImageView) findviewbyid(r.id.imageview6); for (int i=0; i<img.length; i++) img[i].setonclicklistener(new View.OnClickListener() public void onclick(view view) switch (view.getid()) case R.id.imageView1: imgvid = 0; break; case R.id.imageView2: imgvid = 1; break; case R.id.imageView3: imgvid = 2; break; case R.id.imageView4: imgvid = 3; break; case R.id.imageView5: imgvid = 4; break; case R.id.imageView6: imgvid = 5; break; checkresult(imgvid); ); Runnable runnable = new public void run() reset(); handler1.postdelayed(this, 1000); 105

38 ; handler1.postdelayed(runnable, 1000); int getimage(int n) int rid = 0; switch (n) case 0: rid = R.drawable.zombie1; break; case 1: rid = R.drawable.zombie2; break; case 2: rid = R.drawable.zombie3; break; case 3: rid = R.drawable.zombie4; break; case 4: rid = R.drawable.zombie5; break; case 5: rid = R.drawable.zombie6; break; return rid; void reset() for (int i=0; i<img.length; i++) img[i].setimageresource(r.drawable.nozombie); selected_img = rnd.nextint(6); img[selected_img].setimageresource(getimage(selected_img)); void checkresult(int vid) if (vid == selected_img) hit++; else miss++; textview1.settext("hit: " + hit + " Miss: " + miss); reset(); 13. In the tool bar, click the Run ( ) button to test the application. One of the 6 zombies will randomly jump out. Tap on the zombie to earn credits. A sample output looks: 14. Capture a screen shot(s) similar to the above, and paste it/them to the lab3.doc (or.docx) document. 15. Copy the app-debug.apk. file to a temporary directory and rename it to lab3_5.apk. Submittal 1. Compress ONLY the following files to a.zip file named lab3.zip. lab3_1.apk 106

39 lab3_2.apk lab3_3.apk lab3_4.apk lab3_5.apk Lab3.doc (or lab3.docx) 2. Submit only the.zip file as response to Question 11. Programming Exercise #03 1. Create a new Android project named ex Use the Learning Activity #5 as a guideline to create an Android application that will have the following layout in the design view.padding, as shown below. 3. When being played, one of the 9 zombie will randomly jump out. The play must hit the zombie to earn credit. 4. Capture a screen shot similar to the above figure and then paste it to a Word document named ex03.doc (or.docx). 5. Compress the executable (ex03.apk) and the Word document (ex03.doc or.docx) to a.zip file named ex03.zip. 6. Upload ONLY the.zip file. 107