Sample Exam 2 questions

Sample true/false questions

1. The following code fragment (inside main) results in a compiler error:

        for (int i=6; i>0; i++) {
         System.out.println (i);
     }
       

2. It is possible to have method main call method foo, which then calls method bar.
3. A method declared to return an int type does not have to return anything, but a void method cannot return an int.

Sample multiple-choice questions

1. The code below

   public class Test {
       public static void main (String[] argv) 
       {
           int i = 5;
           int[] A = {6};
           change (i);
           System.out.println (i);
           change (A[0]);
           System.out.println (A[0]);
       }
   
       static void change (int i) 
       {
           i = i + 1;
       }
   }
   

   prints
   1. 5, 7
   2. 5, 6
   3. 6, 7
   4. 6, 6
2. For the array A with elements {1,4,9,16,25} the code fragment

      for (int i=1; i<A.length; i++) {
         A[i] = A[i-1];
      }
      System.out.println (Arrays.toString(A));
   

   results in:
   1. {1,1,1,1,1}
   2. {1,1,4,9,16}
   3. {25,1,4,9,16}
   4. An array-out-of-bounds exception
3. Consider the program below

   public class Test {
       public static void main (String[] argv)
       {
   	char[] letters = {'b','a','d','c','a','f','e'};
   	String s = strangeMethod (letters);
   	System.out.println (s);
       }
   
       static String strangeMethod (char[] A)
       {
   	int base = (int) 'a';
   	String s = "";
   	for (int i=0; i<A.length; i++) {
   	    int k = (int) A[i];
   	    if (k < base+2) {
   		s = s + A[i];
   	    }
   	}
   	return s;
       }
   }
   

   This results in:
   1. badcafe
   2. efacdab
   3. baa
   4. dcfe

Sample programming problems

1. Given an array of chars of even length like

       char[] letters = {'a','b','c','d','e','f'};
     

   write a method called mixHalves to return a string with all the odd-positioned letters together followed the even-positioned letters. Thus, for the above, with the call

       String s = maxHalves(letters);
       System.out.println (s);
     

   you should get bdface as the printed string.
2. An int array is palindromic if it looks the same in reverse. Thus,

           int[] A = {1, 2, 3, 2, 1};
           int[] B = {1, 4, 9, 9, 4, 1};
           int[] C = {1, 4, 9, 6, 1};
           System.out.println (checkPalindrome(A));
           System.out.println (checkPalindrome(B));
           System.out.println (checkPalindrome(C));
     

   should print

       true
       true
       false
     

   Write the method checkPalindrome using only while-loops (i.e., without for-loops).