Stack ADT Example in Java

 import java.util.*;  
 class stack  
 {  
      int size,top=-1;  
      int stackAr[];  
      public stack(int size)  
      {  
           this.size=size;  
           stackAr=new int[size];  
      }  
      public void push (int data)  
      {  
           //System.out.println("-------size: "+size);  
           if (top<(size-1))  
           {  
                stackAr[++top]=data;  
                System.out.println("-------top: "+top);  
           }  
           else  
                System.out.println("No space to insert.");  
      }  
      public void pop()  
      {  
           System.out.println("element is removed: "+stackAr[top]);  
           top--;  
      }  
      public void display()  
      {  
           if (top!=-1)  
           {   
                for (int i=0;i<=top;i++ )  
                {  
                     System.out.print(stackAr[i]+"\t");  
                }  
           }  
           else  
                System.out.println("Empty");  
           //System.out.println();  
      }  
 }  
 class StackADT   
 {  
      public static void main(String[] args)   
      {  
           System.out.print("Enter the size of the array:");  
           Scanner scan=new Scanner(System.in);  
           int size=scan.nextInt();  
           stack obj=new stack(size);  
           while (true)  
           {  
                System.out.println("\n1. push.\n2.pop.\n3.display.\n4.exit.\n");  
                int option=scan.nextInt();  
                switch (option)  
                {  
                case 1:  
                     System.out.println("Enter element:");  
                     int data=scan.nextInt();  
                     obj.push(data);  
                     break;  
                case 2:  
                     obj.pop();  
                     break;  
                case 3:  
                     obj.display();  
                     break;  
                case 4:  
                     System.exit(0);  
                default:  
                     System.out.println("wrong input..");  
                }  
           }  
      }  
 }