SELECTIONS - Introduction to Java Programming: Comprehensive Version - page 96

If one of the operands of an && operator is false , the expression is false ; if one of the
operands of an || operator is true , the expression is true . Java uses these properties to
improve the performance of these operators. When evaluating p1 && p2 , Java first evaluates
p1 and then, if p1 is true , evaluates p2 ; if p1 is false , it does not evaluate p2 . When
evaluating p1 || p2 , Java first evaluates p1 and then, if p1 is false , evaluates p2 ; if p1 is
true , it does not evaluate p2 . In programming language terminology, && and || are known
as the short-circuit or lazy operators. Java also provides the unconditional AND ( & ) and OR
( | ) operators, which are covered in Supplement III.C for advanced readers.

short-circuit operator
lazy operator

3.18

✓ ✓

Assuming that x is 1 , show the result of the following Boolean expressions.
( true ) && ( 3 > 4 )
!(x > 0 ) && (x > 0 )
(x > 0 ) || (x < 0 )

Check

Point

(x != 0 ) || (x == 0 )
(x >= 0 ) || (x < 0 )
(x != 1 ) == !(x == 1 )

3.19

(a) Write a Boolean expression that evaluates to true if a number stored in variable
num is between 1 and 100 . (b) Write a Boolean expression that evaluates to true if
a number stored in variable num is between 1 and 100 or the number is negative.

3.20

(a) Write a Boolean expression for x - 5 6 4.5. (b) Write a Boolean expression

for x - 5 7 4.5.

3.21

Assume that x and y are int type. Which of the following are legal Java expressions?
x > y > 0
x = y && y
x /= y
x or y
x and y
(x != 0 ) || (x = 0 )

3.22

Are the following two expressions the same?
a. x % 2 == 0 && x % 3 == 0
b. x % 6 == 0

3.23

What is the value of the expression x >= 50 && x <= 100 if x is 45 , 67 , or 101 ?

3.24

Suppose, when you run the following program, you enter the input 2 3 6 from the
console. What is the output?

public class Test {
public static void main(String[] args) {
java.util.Scanner input = new java.util.Scanner(System.in);
double x = input.nextDouble();
double y = input.nextDouble();
double z = input.nextDouble();

System.out.println( "(x < y && y < z) is " + (x < y && y < z));
System.out.println( "(x < y || y < z) is " + (x < y || y < z));
System.out.println( "!(x < y) is " + !(x < y));
System.out.println( "(x + y < z) is " + (x + y < z));
System.out.println( "(x + y > z) is " + (x + y > z));
}
}

3.25

Write a Boolean expression that evaluates to true if age is greater than 13 and less
than 18 .