Assignment Statements

1. Assignment Statements Operator Precedence

2. total = 55; Assignment, not Equals • An assignment statement changes the value of a variable • The assignment operator is the = sign The expression on the right is evaluated and the result is stored in the variable on the left The value that was in total is overwritten You can only assign a value to a variable that is consistent with the variable's declared type. ICS111-Java Programming Blanca Polo

3. Constants • A constant is an identifier that is similar to a variable except that it holds the same value during its entire existence • As the name implies, it is constant, not variable • The compiler will issue an error if you try to change the value of a constant • In Java, we use the final modifier to declare a constant final int MIN_HEIGHT = 62; ICS111-Java Programming Blanca Polo

4. Constants • Constants are useful for three important reasons • First, they give meaning to otherwise unclear literal values • For example, MAX_LOAD means more than the literal 250 • Second, they facilitate program maintenance • If a constant is used in multiple places, its value need only be updated in one place • Third, they formally establish that a value should not change, avoiding inadvertent errors by other programmers ICS111-Java Programming Blanca Polo

5. No Magic Numbers 3.1416 1.623 37 ICS111-Java Programming Blanca Polo

6. Addition Subtraction Multiplication Division Remainder + - * / % Expressions • An expression is a combination of one or more operators and operands • Arithmetic expressions compute numeric results and make use of the arithmetic operators: If either or both operands used by an arithmetic operator are floating point, then the result is a floating point ICS111-Java Programming Blanca Polo

7. 14 / 3equals 4 8 / 12equals 0 14 % 3equals 2 8 % 12equals 8 Division and Remainder If both operands to the division operator are integers, the result is an integer (the fractional part is discarded) The remainder operator (%) returns the remainder after dividing the second operand into the first ICS111-Java Programming Blanca Polo

8. 4.58064516129 14.2 / 3.1equals 0.67716535433 8.6 / 12.7equals Division with Double numbers If both operands to the division operator are doubles, the result is double number • The remainder operator (%) should not be used with double numbers. • In Java 1.5 it is allowed but it is unpredictable. ICS111-Java Programming Blanca Polo

9. Mixing double and int numbers • We will go over this in our next class. ICS111-Java Programming Blanca Polo

10. Operator Precedence • Operators can be combined into complex expressions result = total + count / max - offset; • Operators have a well-defined precedence which determines the order in which they are evaluated ICS111-Java Programming Blanca Polo

11. Operator Precedence • Arithmetic operators with the same precedence are evaluated from left to right, but parentheses can be used to force the evaluation order ICS111-Java Programming Blanca Polo

12. First the expression on the right hand side of the = operator is evaluated answer = sum / 4 + MAX * lowest; 4 1 3 2 Then the result is stored in the variable on the left hand side Assignment Revisited • The assignment operator has a lower precedence than the arithmetic operators ICS111-Java Programming Blanca Polo

13. First, one is added to the original value of count count = count + 1; Then the result is stored back into count (overwriting the original value) Assignment Revisited • The right and left hand sides of an assignment statement can contain the same variable ICS111-Java Programming Blanca Polo

14. count = count + 1; Assigning the value to the left side Into a temporary memory space How does this work? • JAVA works the right side of the assignment first • It then stores the result in a temporary memory space • Now it assigns that value into the left side ICS111-Java Programming Blanca Polo

15. Increment and Decrement • The increment and decrement operators use only one operand • The increment operator (++) adds one to its operand • The decrement operator (--) subtracts one from its operand • The statement count++ is functionally equivalent to count = count + 1; ICS111-Java Programming Blanca Polo

16. Increment and Decrement • The increment and decrement operators can be applied in postfix form: count++ • or prefix form: ++count • When used alone it, the postfix is the form used ICS111-Java Programming Blanca Polo

17. int total; int count = 2; • Postfix increments after the assignment: • Assigns the value of count(2) to total making total =2 • Increments count by making count = 3 • At the end total is 2 and count is 3. total = count++; total = count; count=count+1; Increment and Decrement • When used as part of a larger expression, the two forms can have different effects so be careful. ICS111-Java Programming Blanca Polo

18. Prefix increments before the assignment: • Increments count by one making count = 3 • Assigns count (3) to total making total =3 • At the end both total and count are 3. Total = ++ count; Increment and Decrement int total; int count = 2; count = count+1; count = total; ICS111-Java Programming Blanca Polo

19. Assignment Operators • Often we perform an operation on a variable, and then store the result back into that variable • Java provides assignment operators to simplify that process • For example, the statement num += count; is equivalent to num = num + count; ICS111-Java Programming Blanca Polo

20. Operator += -= *= /= %= Example x += y x -= y x *= y x /= y x %= y Equivalent To x = x + y x = x - y x = x * y x = x / y x = x % y Assignment Operators – shortcuts • There are many assignment operators in Java, including the following: No need to use shortcuts just take the long way. It works!!! ICS111-Java Programming Blanca Polo

21. Precedence Increment and Decrement Arithmetic Operators ICS111-Java Programming Blanca Polo