How to resize an array in Java?

An array cannot be resized dynamically in Java. 

• One approach is to use java.util.ArrayList(or java.util.Vector) instead of a native array.
• Another approach is to re-allocate an array with a different size and copy the contents of the old array to the new array.

Example:

class ResizableArray {
   public static void main (String[] args) {
         int[] a = {1, 2, 3};
         a = (int[])resizeArray(a, 5);
         a[3] = 4;
         a[4] = 5;
         for (int i=0; i<a.length; i++)
            System.out.println(a[i]);
  }
      private static Object resizeArray (Object oldArray, int newSize) {
            int oldSize = java.lang.reflect.Array.getLength(oldArray);
            Class elementType = oldArray.getClass().getComponentType();
            Object newArray = java.lang.reflect.Array.newInstance(elementType, newSize);
            int preserveLength = Math.min(oldSize, newSize);
               if (preserveLength > 0)
                  System.arraycopy(oldArray, 0, newArray, 0, preserveLength);
            return newArray;
      }
}

Output:

1
2
3
4
5