Chapter 3 - Selections

Question 1

What does &&, ||, and ! mean in boolean expressions?

Answer 1

&& means AND
|| means OR
! means NOT

Question 2

What 3 types of selection statements are there?

Answer 2

if-else statements, switch-statements, and conditional expressions

Question 3

What types can be in a switch expression?

Answer 3

char, byte, short, int, or String

Question 4

What happens if you omit a break statement in a case?

Answer 4

The program will continue to the next case, instead of exiting the switch construct

Question 5

What is 1.0 + 1.0 + 1.0 + 1.0 + 1.0 == 5.0?

A. true
B. false
C. other

Answer 5

C. other.

There is no guarantee that 1.0 + 1.0 + 1.0 + 1.0 + 1.0 == 5.0 is true, becuase floating-point numbers are approximated.

Question 6

Analyze the following code:

boolean even = false;
if (even = true) {
System.out.println(“It is even!”);
}

A. The program has a compile error.
B. The program has a runtime error.
C. The program runs, but displays nothing.
D. The program runs and displays It is even!

Answer 6

The correct answer is D
Explanation: It is a common mistake to use the = operator in the condition test. What happens is that true is assigned to even when you write even = true. So even is true. The program compiles and runs fine and prints ‘It is even!’.

Question 7

Code 1:

int number = 45;
boolean even;

if (number % 2 == 0)
even = true;
else
even = false;

Code 2:

int number = 45;
boolean even = (number % 2 == 0);

A. Code 1 has compile errors.
B. Code 2 has compile errors.
C. Both Code 1 and Code 2 have compile errors.
D. Both Code 1 and Code 2 are correct, but Code 2 is better.

Answer 7

D. Both Code 1 and Code 2 are correct, but Code 2 is better.

Question 8

Which of the Boolean expressions below is incorrect?

A. (true) && (3 => 4)
B. !(x > 0) && (x > 0)
C. (x > 0) || (x < 0)
D. (x != 0) || (x = 0)
E. (-10 < x < 0)

Answer 8

A, D and E are incorrect.

Explanation: a: (3 => 4) should be (3 >= 4), d: (x = 0) should be (x == 0), and e: should be (-10 < x) && (x < 0)

Question 9

Suppose x=10 and y=10 what is x after evaluating the expression (y > 10) && (x++ > 10).

A. 9
B. 10
C. 11

Answer 9

B. 10

Explanation: For the && operator, the right operand is not evaluated, if the left operand is evaluated as false.

Question 10

Suppose x=10 and y=10 what is x after evaluating the expression (y >= 10) || (x++ > 10).

A. 9
B. 10
C. 11

Answer 10

B. 10

Explanation: For the || operator, the right operand is not evaluated, if the left operand is evaluated as true.

Question 11

What is y after the following switch statement is executed?

int x = 3; int y = 4;
switch (x + 3) {
  case 6: y = 0;
  case 7: y = 1;
  default: y += 1;
}

A. 1
B. 2
C. 3
D. 4
E. 0

Answer 11

B. 2

Case 6 is invoked first, but since there’s no break statement in case 6, all the other cases are executed as well.

Question 12

What will be displayed by the following switch statement?

char ch = 'a';

    switch (ch) {
      case 'a':
      case 'A':
        System.out.print(ch); break;
      case 'b':
      case 'B':
        System.out.print(ch); break;
      case 'c':
      case 'C':
        System.out.print(ch); break;
      case 'd':
      case 'D':
        System.out.print(ch);
    }

A. abcd
B. a
C. aa
D. ab
E. abc

Answer 12

B. a

Question 13

Analyze the following program fragment:

int x;
double d = 1.5;

switch (d) {
  case 1.0: x = 1;
  case 1.5: x = 2;
  case 2.0: x = 3;
}

A. The program has a compile error because the required break statement is missing in the switch statement.
B. The program has a compile error because the required default case is missing in the switch statement.
C. The switch control variable cannot be double.
D. No errors.

Answer 13

C. The switch control variable cannot be double.

Question 14

Analyze the following code fragments that assign a boolean value to the variable even.

Code 1: 
if (number % 2 == 0)
  even = true;
else 
  even = false;

Code 2:
even = (number % 2 == 0) ? true: false;

Code 3:
even = number % 2 == 0;

A. Code 2 has a compile error, because you cannot have true and false literals in the conditional expression.
B. Code 3 has a compile error, because you attempt to assign number to even.
C. All three are correct, but Code 1 is preferred.
D. All three are correct, but Code 2 is preferred.
E. All three are correct, but Code 3 is preferred.E. All three are correct, but Code 3 is preferred.

Answer 14

E. All three are correct, but Code 3 is preferred.

Explanation: Code 3 is the simplest. Code 1 and Code 2 contain redundant code.

Question 15

What is the syntax of conditional expressions?

Answer 15

boolean-expr ? expr1 : expr2;

Question 16

What is the output, you you enter the numbers 9, 8 and 6?

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.nextDoubl();
        System.out.println((x > y && y > z) ? "sorted" : "not sorted");
    }
}

Answer 16

“sorted”