Presentation on theme: "Slide 1 Chapter 4 Assignment Statement An assignment statement gives a value to a variable. Assignment can take several forms: x = 5; a literal (5) is."— Presentation transcript:
Slide 1 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
Slide 2 Chapter 4 Variable Assignment A variable can store only one value at any time. int x; x = 5; x = 10; x 5 10
Slide 3 Chapter 4 Primitive Data Types TypeStorage Required int 4 bytes double 8 bytes char 2 bytes boolean 1 bit
Slide 4 Classic Asteroids Game from Atari
Slide 5 A variable declared with a class is called an object. For example, the object a47 is type Asteroid: Asteroid a47 = new Asteroid();a47 a47.setLocation(x,y) a47.destroy()
Slide 6 Chapter 4 Java Packages Numerous packages are included with JRE (Java Runtime Environment) Packages contain classes Packages can be added to an application with an import statement. For example, the statement import java.util.Scanner; makes the Scanner class and its methods accessible to the application.
Slide 7 Chapter 4 The Scanner Class Part of the java.util package import java.util.*; A Scanner object processes text and numbers from the input stream Methods include: next() nextLine() nextInt() nextDouble() nextBoolean() close()
Slide 8 Chapter 4 Integer Division Integer division ( / ) is performed when both operands are integers. Only the integer portion of the quotient is returned: int answer; answer = 20 / 7; System.out.print(answer); Output 2 Source Code
Slide 9 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
Slide 10 Chapter 4 Modulus Division Modulus division ( % ) returns the remainder of a division operation: int answer; answer = 20 % 7; System.out.print(answer); Output 6 Source Code
Slide 11 Chapter 4 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
Slide 12 Chapter 4 Changing the Order of Operations 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
Slide 13 Chapter 4 Type Casting Assigning an integer value into a floating-point variable works just fine. For example: double bankAccountBalance = 1000; However assigning a floating-point value into an integer variable is like trying to fit a large object in a small box. By default, Java treats it as an illegal operation. For example, this causes an error: int temperature = 22.8;
Slide 14 Chapter 4 Type Casting 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
Slide 15 Chapter 4 Assignment Operators OperatorOperation += addition and then assignment -= subtraction and then assignment *= multiplication and then assignment /= division and then assignment %= modulus division and then assignment
Slide 16 Chapter 4 Named Constants A named memory location that cannot be changed from its initial value. The keyword final is used in a constant declaration. Constant identifiers are typically all uppercase with an underscore ( _ ) separating words within the identifier name.
Slide 18 Chapter 4 Programming Errors Syntax errors violate the rules of Java. 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.