Lecture 2 Announcements

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2 Lecture 2 Announcements Home Computers and/or Laptops/Notebooks By now you should have installed Java SE 8 and jgrasp on your computers, set up the becker.jar file, and started working with some of the supplied.java files from Lecture 1. How many have done this successfully? How many have tried to do this and have still not gotten jgrasp to compile and run? If you have your laptops with you, I will stick around for a bit after today's class to see if we can get you up and running. I'll also stick around for a bit after next Wednesday s class. I've added a TROUBLESHOOTING walk-through page to the BIT115 website if you are getting the jgrasp wedge2 PATH error. This should be fixed with the latest version of jgrasp, but just in case IMPORTANT! Always download the.java files from the web site, save them to a local folder, and run them from there. If you try to run them directly off the site, they go in the browser cache and get renamed, and then things won't work! There are other issues to remember, which we'll cover in today's class. NOTE: It is essential that you get jgrasp working on your home machines or laptops if you are going to be successful in this class (unless you are going to do all your coding on the PCs here at the college).

3 Setting Up Cascadia Accounts Online 3

4 Assignment Dates (By Due Date) Assignment 1 (LECTURE 5) Section 1: Monday, January 22 nd The Fickle Finger of Fate Assignment 2 (LECTURE 8) Section 1: Wednesday, January 31 st Assignment 1 Revision (LECTURE 10) Section 1: Wednesday, February 7 th Assignment 2 Revision (LECTURE 12) Section 1: Wednesday, February 14 th Assignment 3 (LECTURE 13) Section 1: Wednesday, February 21 st Assignment 3 Revision (LECTURE 16) Section 1: Monday, March 5 th Assignment 4 (LECTURE 18) NO REVISION AVAILABLE! Section 1: Monday, March 12 th 4

5 It's okay if right now you are feeling somewhat overwhelmed, nervous, confused, or just scared spitless! Hey! You're learning a new language (Java) and a new way of thinking about things, so it is perfectly natural if you're feeling a bit overwhelmed right now, or a bit nervous, or even a bit confused. Knowing this, we'll be taking baby steps for the next few lectures. I'll be holding your hand and walking you through Java and code step-by-step. So: Do not be afraid to ask questions! And: Do not be afraid to come see me during my office hours Tuesdays/Thursdays 9:00am-10:30am either in CC3-321 or CC2-180 Also: please me at cduckett@cascadia.edu if you have any questions. If it concerns code that you are working on please remember to attach the.java file to the so I can have a look to determine where a problem might be. Finally: Once I know the exact days, times, and places, going to the Open Labs for additional one-on-one help is greatly encouraged! 5

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7 The Best Way to Learn How to Code is to Code! Code a little bit every day! Practice practice practice! Don't be afraid to take chances, try new things, or experiment. Coding knowledge comes by doing, not by wishful-thinking, magic, or osmosis! Take advantage of resources found on the Internet! Google it! It Compiled!

8 Some Sites/Links of Interest Udacity Free Online Courses MIT OpenCourseWare Free Online Courses Coursera Free Online Courses Standford Engineering Everywhere Online CS Courses Academic Earth Online CS Courses Free Code Camp Online CS Courses Khan Academy Free Online Tutorials Code Academy Interactive Code Learning Code School Interactive Code Learning CoderDoJo Code Club Community Code.org Code Club Community Girls Who Code Code Club Community Girl Develop It Code Club Community 8

9 Lecture 2 Reading Topics Reading Assignment for Today Chapter 1.5: Types of Errors Chapter Tracing Code Note: there are BIT 115 Student Open Source Guides that students wrote from previous quarters that may deal with the various topics of your readings and lessons. This is a great tool, and highly recommended! 9

10 Quarter-Long Game Plan: Up until the Mid-Term: 1 st part of the quarter Overview of topics, conceptual understanding, not as much freeform problem-solving After the Mid-Term: 2 nd part of the quarter Focus on learning and more problem-solving on your own 10

11 Save A Copy Of All Work (Highly recommended!) In-Class Exercises, Exams, Quizzes, etc. If you work with someone, make sure each of you gets a copy For In-Class Exercises, you do not have to turn it in (I ll be checking it as I walk around and watch you work) If you lose track of it, and I unintentionally record it incorrectly in StudentTracker, then whatever I ve got will stand as the grade. Best then to save your work for proof, if needed, in the event of a discrepancy. If you do find a grading error in StudentTracker, then please don't hesitate to let me know! 11

12 Quizzes and Exams Starting next lecture, Lecture 3, you should assume that the quizzes and exams will all be 100% pen/pencil-and-paper. You bring the pen or pencil, I ll supply the paper Start Practicing Now (My Mantra: Practice! Practice! Practice!) Try writing code from memory, and/or using Notepad or NotePad++ and then copy-and-pasting into jgrasp to check your work 12

13 H Assignment 1 is due LECTURE 5 O M E W O R K in StudentTracker by midnight It s posted on the website under Assignments It will be due by midnight on day of Lecture 5, Monday, January 22 nd If you are confused, bring your work to class, in electronic form, and we will go over how to hand in (upload) the homework: Student Tracker (We ll go over this in a moment with Rex Winkus ) How to Use Student Tracker (Instructions) If you re stuck, seek help! Talk to the Instructor or a classmate or Open Lab helper me BIT 115: Introduction To Programming 13

14 A Quick "Peek" at Assignment 1 Let's Have a Quick Look at Assignment 1 (so there are no surprises down the road!) Assignment 1 is due LECTURE 5, Monday, January 22 (uploaded to StudentTracker by midnight) What You Need To Turn In to StudentTracker for A1 A1_Part_1.java A1_Part_2.doc A1_Part_3.doc A1_Part_4.doc A1_Part_5.java (You'll create this from Starting_Template.java file) Personal Data Sheet (Optional).java file only (no.class) MS Word.doc MS Word.doc MS Word.doc.java file only (no.class) MS Word.doc 14

15 NO Warm-Up QUIZ TODAY We will have our very first 'warm-up' Quiz starting Lecture 3 BIT 115: Introduction To Programming 15

16 StudentTracker Reminder 16

17 Today s Topics Dissecting the Code: What it means and what it does opening and working with.java Files jgrasp: Another Look Errors: How to find and fix them How to set up a City Tracing Code Predicting What A Program Will Do BEFORE you Run It Important Java and OOP Terms like Class, Object, Method, Parameter, etc BIT 115: Introduction To Programming 17

18 Dissecting the Software Dissecting the Code 18

19 What Happened When You Installed Java Java Virtual Machine (JVM) Consists of Many Different Components (Classes) That Allow Java Programs to Do Different Things 19

20 What Happened When You Installed Java 20

21 What Happened When You Installed jgrasp 21

22 What Happens When You Add Becker.Jar to jgrasp Path 22

23 What Happens When You Add Becker.Jar to jgrasp Path 23

24 Downloading and Working On.java Files Important Always download the.java files from the web site first to a folder on your computer or USB thumb drive before opening and working on them. If you work on files from the browser cache, the file names can be changedunder and thencourse class name Wide will Information no longer match up and your programs won t run correctly. Also the browser cache likes to append numbers to the file name if you have already downloaded that file previously, which also means the class name won t match the file name..java Files Should Be Associated to jgrasp If you have the Java JDK and jgrasp properly installed, the.java files you download from the BIT115 web site should be associated with jgrasp. This means they will appear with with jgrasp G icon. Typically, all you have to do to open a.java file is to simply double-click on it and it will open automatically in jgrasp. Alternatively, you can open jgrasp and select the file from the menu bar through File > Open or else to the simply drag-and-drop the file into the work window. 24

25 Two Types Files for a Compiled Program:.java and.class When you write a Java program, you will do so a GUI* Java compiler like jgrasp which also doubles as an IDE** When writing Java and saving Java code you do so in a.java file which is a basic text file. It contains human readable text code at least it is readable for some humans. When you compile your Java code into a working Java program, it creates a.class file which is what the computers uses to line everything up in memory and to run the program. It does not consist of human readable text, but rather machine code or byte code. The reason that each of your.java files are built inside of classes in the code are so your computer can find and run the program after it is compiled, since the class files that are created contain language only the computer understands. So, in other words, a class is another name for the idea of a mini-program which only becomes real (in the virtual sense) once the program is successfully compiled. * Graphic User Interface ** Integrated Development Environment

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29 Dissecting the Code: What It Means and What It Does (Quiz2.java) // Lecture 2: Quiz 2 Java file for use with the PowerPoint slides ///////////////////////////////////////////////////////////////// import becker.robots.*; public class Quiz2 extends Object { public static void main(string[] args) { City toronto = new City(6, 12); Robot Jo = new Robot(toronto, 3, 0, Direction.SOUTH, 0); new Thing(toronto, 3, 2); new Wall(toronto, 3, 3, Direction.EAST); new Wall(toronto, 3, 3, Direction.NORTH); new Wall(toronto, 3, 3, Direction.SOUTH); } } Jo.turnLeft(); Jo.move(); Jo.move(); Jo.pickThing(); Jo.move(); Jo.putThing(); Let s download and run the Quiz2.java program to see what it does, and then we will go over all of the parts of its code line-by-line and discuss what it means.

30 import becker.robots.*; becker.jar This imports from the becker.jar collection all the classes contained in the robots file so they would be functionally available in Java (JDK) and any code written using it. These classes include the Robot.class, the Thing.class, the City.class, the Wall.class, and over a hundred more. NOTE: Java loads some classes by default into the compiler, while others it does not. Later on we will have to import additional Java classes in our code to get our programs to work 30

31 public class Quiz2 extends Object public class Quiz2 extends Object 'public' so other classes can use it if need be. a 'class' is a blueprint for making 'objects' that can do something 'Quiz2' is the name of the class. It can be any name (but must match file name if it contains main). The program uses this name when it runs to know what 'objects' and 'methods' to use in the program. Java, like other object-orientated languages, supports class inheritance. Inheritance allows one class to "inherit" the properties of another class. For example, all Java objects are inherited from the java.lang.object class which is a fundamental part of Java and the Java libraries. Our Quiz2 class is inheriting the properties of Java's Object class, and so extends its actions and attributes in the program hierarchy. 31

32 Curly Braces '{' and '}' (I call them "Squiggles") All java programs use opener curly braces { and closer curly braces } as part of its program. Every opener curly brace { must have a closer curly brace } or the program will not compile. The curly braces (or as I like to call them "squiggles") are used to separate the program into smaller zones. These zones in programming jargon are called scope. It is always best to line up the squiggles to make it easier to see the scope and also to troubleshoot the code when things are not working as planned. Let's have a look Opener Opener Scope Closer Scope Closer 32

33 Note: main is a method() inside a Class public static void main(string[ ] args) The method is public because it is accessible to the JVM (Java Virtual Machine) to begin execution of the program, and can be accessed by any other class or method. The static keyword signifies the fact that this method can be invoked without creating an instance of that class (an object). Main is called before any objects are made, hence static. void signifies that this method does not return anything. In other words no new or altered data is sent out from it for use by the rest of the program. Nothing is returned, so void. Just like in the C procedural language and other languages, this is the main method in a Java program. When you run a Java program, execution begins in the main method. String is the data type that could be passed to the method, although no data type needs to be passed. An example of a data type is an int or float. The [] represents unknown quantity. args is the name of the parameter. We can pass any number of arguments to this method. 33

34 City toronto = new City(); Names the object Creates the new City object We want to make a new instance of the City class (City.class) found in the becker > robots directory (inside becker.jar) and call this new object toronto The City class contains all the attributes and actions necessary to set up a city when a named city object (like toronto) is created, include shape, size, color, streets, avenues, etc. By itself, the City class can't do anything. It's just a collections of ideas and concepts. You need an object made from the City class (like toronto here) to actually do something with a city. NOTE: In Java, '=' is an assignment operator, and points right to left; "==" is an equals sign. EXAMPLE: x = 1 assigns 1 to variable space x and x == 1 means x equals 1. 34

35 // Lecture 2: Quiz 2 Java file for use with the PowerPoint slides ///////////////////////////////////////////////////////////////// import becker.robots.*; public class Quiz2 extends Object { public static void main(string[] args) { City toronto = new City(6, 12); Robot Jo = new Robot(toronto, 3, 0, Direction.SOUTH, 0); new Thing(toronto, 3, 2); new Wall(toronto, 3, 3, Direction.EAST); new Wall(toronto, 3, 3, Direction.NORTH); new Wall(toronto, 3, 3, Direction.SOUTH); } } Jo.turnLeft(); Jo.move(); Jo.move(); Jo.pickThing(); Jo.move(); Jo.putThing(); 35

36 Now what about the Robot line of code? What does that all mean? Robot Jo = new Robot(toronto, 3, 0, Direction.SOUTH, 0); The best way to figure this out is to have a look at the Becker Library which gives us information about that becker.jar file we are associating with our programs. Referencing the Becker Library will help us to know how the objects of the Robot class are setup and what methods they can use. Let s have a look at the Becker Library! 36

37 Becker Robot Library Using it to determine class setup and method use In the BIT115 website, under the LIBRARIES & SPECIFICATIONS heading, click on the Becker Robot Library link. This link takes you to the Becker Libraries located at: Robot Jo = new Robot(toronto, 3, 0, Direction.SOUTH, 0); 37

38 In the upper left-hand column, select becker.robots, then in the lower left-hand column select Robot to bring up information about the Robot class

39 In the right-hand column, scroll down to the Constructor Summary section. You will see that there are two types of constructor types available for the construction of a Robot object from the Robot class, one that uses four (4) slots and one that uses (5) slots. The four-slot constructor is used when you want to create a Robot object that does not need to work with things (either pick up things or put down things). The five-slot constructor is used when you want to create a Robot object that does work with things (either pick up things or put down things). So what do the four- or five-slot constructors represent? Let s see on the next slide Not to worry: we will talk about constructors and how they work in Lecture 3.

40 The four-slot constructor is used when you want to create a Robot object that does not need to work with things. It has four slots for the City name, Street location, Avenue location, and Direction facing The five-slot constructor is used when you want to create a Robot object that does work with things. It has four slots for the City name, Street location, Avenue location, Direction facing, and Number of Things in its Backpack. Again: we will talk about constructors and how they work in Lecture 3.

41 So, when we see a line of code like this, it is showing us that we are using the 5-slot constructor: Robot Jo = new Robot(toronto, 3, 0, Direction.SOUTH, 0); Again: we will talk about constructors and how they work in Lecture 3.

42 Robot Jo = new Robot(toronto, 0, 3, Direction.NORTH, 0); Names the Robot Creates the new Robot using five parameters Our instance of the Robot object is named Jo Jo is placed in a City called toronto Jo is starting out on Street 3 Jo is starting out on Avenue 0 Jo is starting out facing SOUTH Jo is starting out with 0 (zero) Things in its backpack Now, another way to "construct" this is with only four parameters, by leaving on the number of Things in the backpack Robot Jo = new Robot(toronto, 3, 0, Direction.SOUTH); If you are not going to be picking up or putting down Things in your program, then you can "construct" your Robot without this fifth parameter used by the backpack. Later on, when we start creating our own types of Robots and methods, some of the ICES will be set up in such a way that parts of the code will use five parameters and other parts of the code will use four parameters and this will cause an error. We'll go over this in greater detail when the time comes. 42

43 new Thing(toronto, 3, 2); new Wall(toronto, 3, 3, Direction.EAST); new Wall(toronto, 3, 3, Direction.NORTH); new Wall(toronto, 3, 3, Direction.SOUTH); These will work by default. For stuff that just sits there, we don t have to actually give them unique names (e.g., BrickWall) but we can t talk about them in code, however a Robot can pick up/put down an unnamed object. Why would you want to give a wall a unique name? If you look at the becker library you will discover that Wall actually extends Thing, that is to say Wall has inherited all the initial properties of Thing Jo.move(); move() is one of the methods of the Robot class, along with turnleft(), pickthing(), putthing(), as well as frontisclear(), countthingsinpackback(), and several more. Because Robot class has a move() command, Jo can use move(). BIT 115: Introduction To Programming 43

44 Something to Remember: In parameter order, street comes first and avenue comes second. Streets go West-East (left-right) Avenues go North-South (up-down) A neat trick to remember the difference is to recall that the 'A' and 'V' in Avenue point up and down.

45 Three Types of Errors 45

46 Chapter 1.5: Types of Errors 3 Different General Categories of Errors: Compile-Time Errors (or Syntax Errors) Run-Time Errors (or Application Errors) Intent Errors (or Logical Errors) 46

47 An Historical Side Trip: Why Are Bugs Called Bugs? Use of the term "bug" to describe inexplicable defects has been a part of engineering jargon for many decades and predates computers and computer software; it may have originally been used in hardware engineering to describe mechanical malfunctions. For instance, Thomas Edison wrote the following words in a letter to an associate in 1878: It has been just so in all of my inventions. The first step is an intuition, and comes with a burst, then difficulties arise this thing gives out and [it is] then that "Bugs" as such little faults and difficulties are called show themselves and months of intense watching, study and labor are requisite before commercial success or failure is certainly reached. In 1946, when computer pioneer Grace Hopper joined the Harvard Faculty at the Computation Laboratory to work on the Mark II and Mark III computers. Operators traced an error in the Mark II to a moth trapped in a relay, coining the term bug. This bug was carefully removed and taped to the log book. Stemming from the first bug, today we call errors or glitches in a program a bug. 47

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49 Compile-Time Errors (or Syntax Errors) Anything that goes wrong when you compile the file is a compile-time error! Point out that the Output Panel is often small, but it can be resized, and you should get used to figuring out which line the error pertains to. Java is case sensitive - Java is different from java, is different from JaVa, is different from JAVA - This means you must type names, etc, EXACTLY the same File name MUST be the same as the class name that has the main method You need the import becker.robots.*; at the top of each robot file Forgetting to Compile BEFORE Running - You need to compile the file EVERY SINGLE TIME you change it - You should also wait UNTIL the compilation finishes BEFORE trying to run it Strategy For Fixing Compile-Time Errors: Follow the debugging strategy (listed in your text) to find and correct the syntax errors in the FindErrors.java program later this evening when you do your In-Class Exercises. 1. Compile the program to get a list of errors; 2. Fix the most obvious errors, beginning with the first error reported 3. Compile the program again to get a revised list of the remaining errors. 49

50 Run-Time Errors (Application/Crashing Errors) Anything that causes the software application (jgrasp) to crash while it's running is known as a Run-Time Error. If you encounter a run-time error when you are compiling and running your Java programs, then this would be a jgrasp problem, or a Windows Operating System problem, and NOT a Java Problem. The Java language does a lot to protect you from this type of error, so you shouldn't see many of these. Intent Errors (Logical Errors) The program compiles and runs without crashing, but it does not do what you intended is a Intent Error (also called a Logical Error). Example: - Robot takes an extra leftturn, and runs off the screen - Robot doesn't pick up a Thing when it's supposed to. - Robot collides with a Wall (the book calls this a run-time error, but it technically isn t) As you continue learning to code you'll make fewer "typo" type mistakes, and end up with more Intent errors then Compile-Time errors. You need to come up with a personal strategy to figure out where the Intent problems are, and how to fix them. One Option: Use a Program Debug Table (show where this is on web site) 50

51 Lecture 2 ICE: Finding And Fixing Errors In Your Program In-Class Exercise Directions 2.1 FindErrors.java Program Debug Table We'll Wait and Do All the ICEs Together at the End of Lecture BIT 115: Introduction To Programming 51

52 Lecture 2 ICE: Setting Up a City In-Class Exercise Directions 2.2 Starting_Template.java We'll Wait and Do All ICEs Together at the End of Lecture BIT 115: Introduction To Programming 52

53 Chapter Tracing Code BIT 115: Introduction To Programming 53

54 BIT 115: Introduction To Programming 54

55 BIT 115: Introduction To Programming 55

56 Important Terms to Remember 56

57 Some Important Terms To Remember A class is a set of functions that can work together to accomplish a task. It can contain or manipulate data, but it usually Under does Course so according Wide to a pattern Information rather than a specific implementation. An instance of a class is considered an object. Until an object is instantiated from a class, the class can t actually do anything. An object receives all of the characteristics of a class, including all of its default data and any actions that can be performed by its functions. The object is for use with specific data or to accomplish particular tasks. A method simply refers to a function that is encased in a class. It usually entails an action. A parameter is a variable that is passed into a function that instructs it how to act or gives it information to process. Parameters are also sometimes called arguments. A field or property is a default set of data stored in a class. A class can have multiple properties and can be changed dynamically through the methods of the class. These are sometimes called attributes. Inheritance is one of the keys that make OOP tick. Simply put, classes can inherit methods and fields from other classes by extending them and each class can be extended by multiple classes. This means that you can start with a base (or parent) class that contains shared characteristics among several classes. That base class can then be extended by other classes (children) that are similar but are meant for slightly different purposes. Any changes in the parent class will automatically cascade to its children. BIT 115: Introduction To Programming 57

58 Class (The Idea of Attributes and Actions, Features and Functions) A class is a collection of functions that can work together to accomplish a task. It can contain or manipulate data, but Under it usually Course does so according Wide to a Information pattern rather than a specific implementation. An instance of a class is considered an object. Until an object is instantiated from a class, the class can t actually do anything. Example The Robot class. The Robot class contains all the attributes and actions that a robot might have once it is created (or instantiated) as an object. Until then, all the Robot features and functions are just the idea how a robot might work, but being an idea the class doesn t do any work itself. So, a class is like a blueprint, and an object is what is built from the blueprint. Just like we might have an idea how a car should look and operate body, engine, four tires, steering wheel, gas and brake pedals, etc an idea of a car is not the same of an actual working car. Here the idea of a car is a class, and an actual working car is an object. BIT 115: Introduction To Programming 58

59 "Brakes" "Engine" "Lights" "Transmission" "Wheels" "Chassis" "Seats" "Power" "Car" Class "Car" Object 59

60 "Brakes" No "Wings Here "Engine" "Lights" "Transmission" "Wheels" "Chassis" "Seats" "Power" "Car" Class "Car" Object 60

61 Object (An Instance of the Idea Made Actionable) An object receives all of the characteristics of a class, including all of its default data and any actions that can be performed by its functions. The object is for use with specific data or to accomplish particular tasks. Under Course Wide Information Example When we create an object from the Robot class we do so by creating a named instance of the Robot class that will possess all the features and functions that were outlined as belonging to the Robot class as an idea. Once the object is instantiated, what was once the idea of a Robot now becomes an actual Robot that possesses specific Robot properties (its shape, size, color, speed) and that can perform specific Robot actions (like move, turn left, put down a thing, pick up a thing, etc). BIT 115: Introduction To Programming 61

62 Method (An Action That Might Be Performed by the Object) A method simply refers to a function that is encased in a class. It usually entails an action. Example After we have created a named object from the Robot class that possesses all the properties (or attributes) belonging to robots, the robot can now perform some kind of action or actions (like move, turn left, put down a thing, pick up a thing, etc). These actions are the methods belonging to the Robot classes, and which an instance of the Robot class can perform. A robot can move because the Robot class has a method called move() which will allow the robot to move one space forward each time it is called upon to do so. Although we might want the robot to mix a martini, the robot can not because the Robot class does not contain a mixamartini() method. Later on in this course we will learn how we might make a new kind of class that could contain a mixamartini() method, but the Robot class we are using now does not have just such a method. BIT 115: Introduction To Programming 62

63 Parameter ( Information or Instruction That Might Be Given) A parameter is a variable that is passed into a function that instructs it how to act or gives it information to process. Under Parameters Course are also Wide sometimes Information called arguments. Example When we have a robot object call upon a method in order to perform some action, that method may or may not take a parameter which is an additional piece of information or an instruction that might extend its functionality. Currently most of the methods belonging to the Robot class do not take any parameters (although in a moment we ll look at a Robot method that does take a parameter). For example, the move() method when called upon will allow the robot to move one space forward. You ll notice that the move() method has two empty parentheses which represents that it doesn t take a parameter. Had the programmer of the Robot class designed the move() method differently, then it might have taken a parameter to represent how many places the robot should move. For example move(1) might make the Robot move one space forward, move(2) might make the Robot move two spaces forward, move(3) might make the robot move three spaces forward, and so on. Since the programmer did not design the move() method this way, using the move() method like this will not work. This was only a theoretical example. 63

64 Field or Property (The Attributes of Class and Its Objects) A field or property is a default set of data stored in a class. A class can have multiple properties and can Under Course Wide Information be changed dynamically through the methods of the class. These are sometimes called attributes. Example When we create a named instance of a robot from the Robot class, this robot object comes with a set of predefined properties and attributes. For example, by default the new robot object is so many pixels high and so many pixels wide, its shape is an arrowhead, its color is red, and its location and placement and direction in the City is defined by the parameters that were passed to it (which we will discuss in the next Dissecting the Code section). For example, one of the properties of the Robot class is that a robot will move one space forward in.5 seconds. This speed,.5 seconds, is a pre-defined property of the Robot class and any instances of objects made using the Robot class. Now these pre-defined properties might be changed dynamically while the program is running if just such a feature was developed programmatically to do so. In the case of the robot s default speed of.5 seconds for every move, there is a setspeed() method which can be used to change the robot s initially defined speed. For example setspeed(4) will move the Robot twice as fast (the default speed is 2). 64

65 Inheritance (Extending a Class s Features to a New Class ) Inheritance is one of the keys that make Object-Oriented Programming tick. Simply put, classes can inherit methods and fields from other classes by extending them and each class can be extended by multiple classes. Under This means Course that youwide can startinformation with a base (or parent) class that contains shared characteristics among several classes. That base class can then be extended by other classes (children) that are similar but are meant for slightly different purposes. Any changes in the parent class will automatically cascade to its children. Example We will learn about inheritance and how to put it to good use next week. A brief example what inheritance is can be explained by looking at our Robot class. Right now the Robot class has a turnleft() method but it does not have a turnright() method. If you created a Robot object and wanted it to turn right then you would have to call upon it to turn left three times! Now we might create a new type of Robot class (perhaps called MrRoboto) that would extend all the features and functions of the Robot class (like move(), turnleft(), etc) and also create its own new set of methods (like turnaround(), turnright(), etc). In this example we are using the original Robot class to create our new MrRoboto class, and as such the MrRoboto class is inheriting all the original features and functions of the Robot class. This is a great tool of Object Oriented Programming (or OOP) because this means the programmer doesn t have to code all the Robot class features and functions from scratch to use in the new MrRoboto class. All the programmer has to do is code the new methods (like turnaround() or turnright()) since the MrRoboto class inherited all the original methods (like move(), turnleft(), etc). 65

66 In-Class Exercises (ICEs) Working on In-Class Exercises is essential for learning how to program or code and they have been designed to help you with the Assignments. Today I ve dedicated a lot of time to working on the ICEs so I can see how each of you are coming along. Now is the time to ask questions about anything to do with the ICEs, or seek clarification, or to get confirmation that you re on the right track. In-Class Exercise 2.1 In-Class Exercise 2.2 In-Class Exercise 2.3 IMPORTANT! CityFrame: An older version of becker.jar file contained a class called CityFrame which when used looked something like this: CityFrame City = CityFrame(seattle); This old code will rear its ugly head in the ICEs on purpose as an example of 'legacy' code that no longer belongs in the program. When you see it, it should either be "commented out" or deleted altogether since it will not allow the program to run correctly!

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