Create a Dynamic Array for Stack structure in Java

Question

I am learning the Stack Data Structure. I want to create a dynamic array. When the size is exceeded, I want to create a new array.

Program output:

java.lang.ArrayIndexOutOfBoundsException: 2
must be :50 40 30

The code is as given below:

    class Stack{
      int array[];
      int size;
      int top;

      Stack(int size){
        this.size=size;
        array=new int[size];
        top=0;
       }

       public void push(int a){
          if(top>=size){
          int array2[]=new int[size*2];
          for(int i=0;i<size;i++){
            array2[i]=array[i];
          }
          array[top++]=a;
          }
          else{
            array[top++]=a;
          }
        }
        public int pop(){
          return array[--top];
      }
    }

    public class Stack1 {

    public static void main(String[] args) {
       Stack y=new Stack(2);
       y.push(10);
       y.push(20);
       y.push(30);
       y.push(40);
       y.push(50);

       System.out.println(y.pop());
       System.out.println(y.pop());
       System.out.println(y.pop()); 
    }
 }

Answer 1

You are creating a new array with a doubled size when the original array is full, but then you do nothing with the new array.

Change your code to :

public void push(int a){
  if(top>=size){
    int array2[]=new int[size*2];
    for(int i=0;i<size;i++){
      array2[i]=array[i];
    }
    array = array2; 
    size *=2;
  }
  array[top++]=a;
}