Simple Java questions

[Junaid Mahmud]

I have to turn in this assignment and would appreciate it if you could go over my answers. You don't have to tell me the answer just tell me what question is incorrect. Thanks!

1. What is y after the following switch statement?

        int x = 0;
        int y = 0;  
        switch (x + 1)  {
            case 0: y = 0; 
            case 1: y = 1; 
            default: y = -1;
        }
 y = -1 
 
 2. Assume x is 0. What is the output of the following statement?

if (x > 0)
      System.out.print("x is greater than 0");
else if (x < 0)
      System.out.print("x is less than 0");
else
      System.out.print("x equals 0");

 x equals 0
 
 
 3. Analyze the following two codes and indicate if the code is correct or there is a problem:

Code 1:

boolean even;

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

Code 2:

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

The following two codes are both correct.


4.  What is the output of 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);
        }
The output will be "a"

5.  What is y after the following switch statement is executed?

x = 3;
switch (x + 3) {
    case 6:  y = 0; 
    case 7:  y = 1;
    default: y += 1;
}
The output of y would be 2

6. Which of the following code displays the area of a circle if the radius is positive.

a.  if (radius <= 0) System.out.println(radius * radius * 3.14159);
b.  if (radius != 0) System.out.println(radius * radius * 3.14159);
c.  if (radius >= 0) System.out.println(radius * radius * 3.14159);
d.  if (radius > 0) System.out.println(radius * radius * 3.14159);

The code: if (radius > 0) System.out.println(radius * radius * 3.14159); will display the area of a circle.


7. If you enter input 9, show the output of the following code:

import java.util.Scanner;

public class Test {
  public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    System.out.print("Enter an integer: ");
    int number = input.nextInt();   

    int i;

    boolean isPrime = true;
    for (i = 2; i < number && isPrime; i++) {
      if (number % i == 0) {
        isPrime = false;
      }
    }

    System.out.println("i is " + i);

    if (isPrime)
      System.out.println(number + " is prime");
    else
      System.out.println(number + " is not prime");   
  }
}

The output of the code is:
Enter an integer: 9
i is 4
9 is not prime

[Jeremy Hutto]

You need to reexamine how switch statements work

[Junaid Mahmud]

Please let me know which questions exactly. Thanks!

[Junilu Lacar]

Is there anything preventing you from putting these into small programs and checking them yourself? I don't see why you have to ask other people to check your answers for you when it would be much quicker for you to do it yourself.

[Campbell Ritchie]

You probably also learn more by trying out little bits of code to see what happens.