JAVA Ch. 4. Variables and Constants Lawrenceville Press

Transcription

1 JAVA Ch. 4 Variables and Constants Slide 1

2 Slide 2 Warm up/introduction int A = 13; int B = 23; int C; C = A+B; System.out.print( The answer is +C);

3 Slide 3 Declaring and using variables

4 Slide 4 Declaring Variables Variable name for a value stored in memory. Variables must be declared before they are used. Variable declarations take the form: <data type> <variable name/identifier>; int length;

5 Slide 5 Using Variables An assignment statement is formed with the variable type and name on the left side of an equal sign; and the value it is to receive on the right side of the equal sign. int A = 40; Operator the equal sign (=) Literal the value to the right of the equal sign.

6 Slide 6 Chapter 4 Assignment Statement An assignment statement gives a value to a variable. Assignment can take several forms: x = 5; a literal (5) is assigned to x x = y + 2; the value of an expression (y + 2) is assigned to x x = z; the value of another variable (z) is assigned to x

7 Slide 7 Using Variables int A = 10; int A; What is the difference between the two assignments statements above? If a variable does not include a literal, that variable s value is going to change as we navigate its class.

8 Slide 8 Chapter 4 Variable Assignment A variable can store only one value at any time. int x; x = 5; x = 10; x 10 5

9 Slide 9 Types of Variables

10 Slide 10 Chapter 4 Primitive Data Types Type Storage Required int 4 bytes double 8 bytes char 2 bytes boolean 1 bit Notes: int integer double decimal number char character boolean true or false

11 Slide 11 Outputting variable values

12 Slide 12 Outputting Variables When outputting variables we must concatenate the value of the variable to a string. To do this we put a (+) in front of the variable name in our output statement. int s = 90; System.out.print( My score is +s out of 100. ); My score is 90 out of 100.

13 Slide 13 Current Class Format

14 Slide 14 /*Name *Date *Class *Period *Class name */ public class ClassName { public static void main(string[] args) { int A = 10; int Variable B = 20; int C; Initialization } C= A + B; System.out.print("this Program statements is my score "+C); }

15 Slide 15 /*Name *Date *Class *Period *Class name */ public class ClassName { public static void main(string[] args) { int A = 10; int B = 80; int C; } C= A + B; System.out.print("this is my score "+C); }

16 Slide 16 Practice -

17 Slide 17 Creating a Ch. 4 Project Create a new project. Call it First initial, last name Chapter 4 BBarrett Chapter 4

18 Slide 18 Practice - In your chapter 4 project, create a class titled: RectanglePerimeter We will do this together In your chapter 4 project, create a class titled: DistancePtOne Pg. 79 You are responsible for completing tis on your own. Mr. Barrett will help you if needed.

19 Slide 19 Java Packages

20 Slide 20 Java Packages Java has tools that are available to the programmer. They are called packages, and Java comes ready equipped for them to be used. These classes contain general utility classes, and special purpose packages. The most fundamental packages is the Java.util.*; package

21 Slide 21 Java Packages: Receiving input from your end-user

22 Slide 22 Java Packages The first package we will introduce will be the: Package. import java.util.scanner; This is the import statement used to make the package accessible to a method/project.

23 Slide 23 Java Packages Instantiation after importing our readymade package, we must initialize the package. This process is called instantiation. The following statement is used to initialize our scanner: Scanner input = new Scanner(System.in);

24 Class importation Slide 24 /* *Name *Date *Class *Period *Class name */ public class ClassName { public static void main(string[] args) { Variable Initialization Package Instantiation Program statements } }

25 Slide 25 import java.util.scanner; /* *Name *Date *Class *Period *Class name */ public class ClassName { public static void main(string[] args) { int x = 10; int y = 5; int c; Scanner input = new Scanner(System.in); - Program statements } }

26 Slide 26 Receiving Data From your end user Part of the java.util.scanner package To receive data from the end user, the following methods are required. Methods include: variablename = input.nextint(); variablename = input.nextline(); variablename = input.next(); variablename = input.nextdouble(); variablename = input.nextboolean(); Input.close();

27 Slide 27 Receiving Data From your end user Methods include: input.nextint(); - integer input.next(); - string input.nextdouble(); - decimal input.nextboolean(); - boolean input.close(); - closes the input stream

28 Slide 28 Receiving data example: import java.util.scanner; int x, y, z; Scanner input = new Scanner(System.in); System.out.print("Enter your first value: "); x = input.nextint(); System.out.print("Enter your second value: "); y = input.nextint(); input.close(); z=x+y; System.out.print("The sum of your numbers is "+z);

29 Slide 29 Abstract Data Types

30 Slide 30 Primitive data types We already discussed primitive data types, i.e., integers, doubles, characters, and Booleans; but there is another type of data that we must cover

31 Slide 31 Abstract Data Types Abstract data type A class. A data type that can store data and methods. Method A named set of statements that perform a single, well-defined task. Object A variable declared with a class.

32 Slide 32 Creating a new object Creating a new object is called instantiation. In addition to declaring a variable to refer to the object, the object must be created and initialized in a statement that takes the form: <class> <variable name> = new <class>(<arguments>);

33 Slide 33 Abstract Data Types Where have we seen this before? <class> <variable name> = new <class>(<arguments>); Scanner input = new Scanner(System.in); Our scanner class is the first abstract data type you have been exposed to.

34 Slide 34 Chapter 4 Abstract Data Types A variable declared with a class is called an object. For example, the object spot is type Circle: Circle spot = new Circle(4); spot getradius() area()

35 Slide 35 Practice

36 Slide 36 Practice In your chapter 4 project, create a class titled: DistancePtTwo Page 82 (bottom) You are responsible for completing this on your own. Mr. Barrett will help you if needed.

37 Slide 37 Algorithms

38 Slide 38 Algorithms Algorithm A set of steps that outline how to solve a problem.

39 Slide 39 Algorithms Algorithm for DistancePtTwo Class 1. Set class template 2. Initialize our variables 3. Initialize our scanner 4. Prompt end user to enter our needed values 5. Calculate the total distance 6. Output total distance

40 Slide 40 Numeric Expressions

41 Slide 41 Numeric Expressions A numeric expression contains at least one operand (a value or primitive variable), and my contain operators.

42 Slide 42 Numeric Expressions Our Operators + : addition - : subtraction / : division % : modulus division (the remainder) * : multiplication = : equals > : greater than < : less than

43 Slide 43 Numeric Expressions Our Operators >= : greater than or equal to <= : less than or equal to!= : not equal to

44 Slide 44 Chapter 4 Integer Division Integer division (/) is performed when both operands are integers. Only the integer portion of the quotient is returned:

45 Slide 45 Chapter 4 Real Division Real division (/) is performed when one or both operands are type double. The entire quotient, including the decimal portion is returned: double result; result = 20.0/7.0; //result is 2.857

46 Slide 46 Chapter 4 Modulus Division Modulus division (%) returns the remainder of a division operation:

47 Slide 47 Chapter 4 Modulus Division 7 % 20 = 7 (zero with a remainder of seven.) 7 %? = (a number between 0 and 6) 100 %? = (a number between 0 and 99)

48 Chapter 4 Slide 48 Operator Precedence Operators in Java have the following precedence: 1. multiplication and division 2. addition and subtraction Operators of the same precedence are evaluated in order from left to right. For example, multiplication is performed first, then division, and finally addition: * 4 / 2 = 17

49 Chapter 4 Changing the Order of Operations Slide 49 The order in which operators are evaluated can be changed by using parentheses. For example, addition is performed first, then multiplication, and finally division: (5 + 6) * 4 / 2 = 22

50 Slide 50 Practice

51 Slide 51 Practice In your chapter 4 project, create a class titled: DivisionOperators Follow along with Mr. Barrett when writing this program. Program found on pages 83 and 84.

52 Slide 52 Practice In your chapter 4 project, create a class titled: Digits Page 84. Write the digits program.

53 Slide 53 Assignment Operators

54 Slide 54 Chapter 4 Assignment Operators Operator Operation += addition and then assignment -= subtraction and then assignment *= multiplication and then assignment /= division and then assignment %= modulus division and then assignment

55 Slide 55 Assignment Operators (+) int A = 10; int B = 5; A += B; System.out.print( Our output is +A); 15

56 Slide 56 Assignment Operators (-) int A = 10; int B = 5; A -= B; System.out.print( Our output is +A); 5

57 Slide 57 Assignment Operators (*) int A = 10; int B = 5; A *= B; System.out.print( Our output is +A); 50

58 Slide 58 Assignment Operators (/) int A = 10; int B = 5; A /= B; System.out.print( Our output is +A); 2

59 Slide 59 Assignment Operators (%) int A = 17; int B = 5; A %= B; System.out.print( Our output is +A); 2

60 Slide 60

61 Slide 61 Type Casting

62 Chapter 4 Type Casting Slide 62 Type Casting converts a number of one type to a number of a different, but compatible type. Type casting is used to: 1. make the operand types in an expression match. For example, wholenum = (int)y * 2 2. truncate the decimal portion of a double. For example, wholenum = (int)z 3. change the way in which a division (/) operation will be performed. For example, realdivision = (double)a / (double)b

63 Slide 63 Type Casting Casting a double to an int truncates, or removes, the decimal portion of the number.

64 Slide 64 Type Casting public class TypeCasting { public static void main(string[] args) { int a = 2; int b = 3; int c; } } c=(double)a*b; System.out.print(+c); 6.0

65 Slide 65 Type Casting: Truncating public class TypeCasting { public static void main(string[] args) { double a = 2.2; double b = 3.1; double c; } } c=a*b; System.out.print(+(int)c); 6

66 Slide 66 Programming Errors

67 Slide 67 Chapter 4 Programming Errors Syntax errors violate the rules of Java. look for the red (X) Logic errors, also called semantic errors, occur in statements that are syntactically correct, but produce undesired or unexpected results. Run-time errors, also called exceptions, halt program execution at the statement that cannot be executed. One type of exception is called InputMismatchException. Look for the error that appears in your console.

68 Slide 68 Practice

69 Slide 69 Practice In your chapter 4 project, create a class titled: GradeAvg1of2 Follow along with Mr. Barrett when writing this program. Program found on page 85.

70 Slide 70 Practice In your chapter 4 project, create a class titled: TempConverter Follow along with Mr. Barrett when writing this program. Program found on page 85.

71 Slide 71 Number Formatting Class

72 Slide 72 Numeric Output The NumberFormat class is used to create objects that format numbers. NumberFormat objects return a string that contains a formatted number. 1. $ , %

73 Slide 73 Numeric Output The number format class allows us to output 1. Money - $x.xx 2. Number Format xx,xxx 3. Decimal - x.xxx 4. Percentage - xx%

74 Slide 74 Numeric Output (step 1) Import the NumberFormating class on line one or two of your class. import java.text.numberformat

75 Slide 75 Numeric Output (step 2) Initialize the format you need to use: 1. NumberFormat money = NumberFormat.getCurrencyInstance(); 2. NumberFormat number = NumberFormat.getIntegerInstance(); 3. NumberFormat decimal = NumberFormat.getNumberInstance(); 4. NumberFormat percent = NumberFormat.getPercentInstance();

76 Slide 76 Numeric Output (step 3) Prepare output statement: 1. System.out.print(money.format(variableName)); 2. System.out.print(number.format(variableName)); 3. System.out.print(decimal.format(variableName)); 4. System.out.print(percent.format(variableName));

77 Slide 77 Numeric Output The number format class allows us to output Money - $x.xx - Number Format xx,xxx Decimal - x.xxx Percentage - xx%

78 Slide 78 Practice In your chapter 4 project, create a class titled: FormattingNumericOutput Copy this class into your chapter 4 project. (P 86)

79 Slide 79 Named Constants

80 Chapter 4 Slide 80 Named Constants A constant is a name for a memory location that stores a value that cannot be changed from its initial assignment. The keyword final is used in the variable s declaration. Constant identifiers are typically all uppercase with an underscore (_) separating words within the identifier name. EX: final int LAST_NUMBER = 100 final double PI = 3.14

81 Slide 81 Public class CircleArea{ public static void main (String[] args){ final double PI = 3.14; double radius = 5; double area; } } area = PI* radius * radius; System.out.print( The area is +area);

82 Slide 82 Final CH 4 Programs

83 Slide 83 Final CH 4 Programs PizzaCost (p.99) Change (p.100) TimeConversion (p.101) Sleep (p.101) Spending (p.102)

84 Slide 84

85 Chapter 4 Slide 85 Java Keywords abstract double int strictfp boolean else interface super break extends long switch byte final native synchronized case finally new this catch float package throw char for private throws class goto protected transient const if public try continue implements return void default import short volatile do instanceof static While

86 Slide 86 Chapter 4 Flowchart Symbols process

87 Slide 87 Chapter 4 The BirthdayGame Flowchart