Self-Review Questions

1. Which of the following statements is a valid array declaration?

   int[] a = new int(30);
   char[] b = new char[0];
   int[] c = new int[][3];
   int[][] d = new int[5][];
   

    

2. What is the value of a[1]?

   int[] a = new int[5];
   

   0

3. What is the value of b[0]?

   int [] a = {1,2,3};
   int [] b = (int[])a.clone();
   if (a == b) b[0]++;
   

   1

4. What is the value of b[0]?

   int [] a = {1,2,3};
   int [] b = (int[])a.clone();
   if (Arrays.equals(a,b)) b[0]++;
   

   2

5. What is the value of twin[1]?

   Object[] obj = {new Integer(10), new String("CMU"), new Double(1.23)};
   Object[] twin = (Object[]) obj.clone();
   obj[1] = new Integer(15);
   

   "CMU"

6. Consider the following code fragment

   int[] a = {1,2,3,4,5};
   foobar(a);
   System.out.println( Arrays.toString(a) );
   

   What will this code print? Does it depend on actual implementation of the foobar() method?

   This code prints the array a after the function foobar is applied to it. It does depend on the actual implementation of foobar().

7. What is the output of this code segment?

   public class Demo
   {
      public static void main(String[] args)
      {
         int[] A = {5, 2, 4, 1, 3};
         action(A);
         System.out.println(Arrays.toString(A));
      }
      public static void action(int[] X)
      {
         Arrays.sort(X);
      }
   }

   [1, 2, 3, 4, 5]

8. Given:

   Object[] A = {new Integer(3), new StringBuffer("circle"),  new ArrayList()};
   Object[] B = new Object[3];
   System.arraycopy(A, 0, B, 0, A.length);
   ((StringBuffer) A[1]).append("s");
   ((ArrayList) A[2]).add("CMU");
   

   What are the results of the following comparisons?

   B == A;
   	false: different objects
   A[0] == B[0];
   	true: same object
   A[1] == B[1];
   	true: same object
   A[2] == B[2];
   	true: same object
   

    

9. Birthday Paradox. Write a method that computes the number of people (by simulation) that must enter a room until two of them share a birthday. Assume that there are 365 possible birthdays, and that birthdays are uniformly distributed throughout the year.

   public int birthdayParadox(){
       Random rand = new Random();
       boolean[] bool = new boolean[356];
       int count = 0;
       while(true){
       	int random = rand.nextInt(356);
           count++;
           if(bool[random])break;
           else
   	    bool[random] = true;
       }
   	return count;
   }