Problem of the Day

Wednesday, January 22, 2025

Problem:

An int Array such as the one shown here is initialized to a size of 10, which results in all of the elements being given an initial value of 0. A series of values are placed into the array, and an int variable size is used to identify both the current number of active values stored there, as well as the index of the next element in the array into which the next value will be placed.

Here, size = 5, indicating both that there are 5 values stored in the array and that the next value to be stored in the array will be placed at position 5.

Consider the following class, which is intended to maintain such a collection of values in an int Array.

public class IntArray
{
    private int[] vals;
    private int size;

    /** 
     * Constructs a new IntArray with the capacity to store 
     * 10 values
     */
    public IntArray()
    {
        // initialise instance variables
        vals = new int[10];
        size = 0;  // indicates both the index where
                   // the next value will be placed and
                   // the "size" of the current number of values
    }

    /* methods not shown */

}

Which of the following methods will correctly add a value to the array and update the value of size appropriately?

1. 
   

   public void add(int value)
   {
       if (size < vals.length)
       {
           vals[size] = value;
           size++;
       }
   }

2. 
   

   public void add(int value)
   {
       if (size < vals.length)
       {
           size++;
           vals[size] = value;
       }
   }

3. 
   

   public void add(int value)
   {
       if (size < vals.length)
       {
           size++;
           vals[0] = value;
       }
   }

4. 
   

   public void add(int value)
   {
       if (size < vals.length)
       {
           vals[0] = value;
           size++;
       }
   }

Show solution: