Array Stack using interface in Java

/*  Stack using interface  */

    import java.io.*;
    interface stack
    {
        void push(int val);
        void pop();
        void display();
        void check();
    }
    class stacktest implements stack
    {
        int top,a[],n;
        stacktest(int cap)
        {
            n=cap;
            top=-1;
            a=new int[n];
        }
        public void push(int val)
        {
            if(top==n-1)
                System.out.println("\nStack overflow .... \n");
            else
                a[++top]=val;
        }
        public void pop()
        {
            int r;
            if(top==-1)
                System.out.println("\nStack underflow...\n");
            else
            {           
                r=a[top--];
                System.out.println("\nDeleted Element : " + r + "\n");
            }
        }
        public void display()
        {
            if(top==-1)
                System.out.println("\nStack Underflow .... \n");
            else
            {
                System.out.print("Stack : ");
                for(int i=top;i>=0;i--)
                    System.out.print(a[i] + "   ");
                System.out.println();
            }
        }
        public void check()
        {
            if(top==-1)
                System.out.println("\nStack empty... no element in stack....");
            else if(top==n-1)
                System.out.println("\nStack full.... no empty space...");
            else
            {
                int s=top+1;
                System.out.println("\nStack contains " + s + " elements");
            }
        }
    }
    class interstack
    {
        public static void main(String args[])throws IOException
        {
            System.out.println("\nProgram to implement stack using interface ");
            int ch,n,val;
            System.out.println("Enter array capacity : ");
            BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
            n=Integer.parseInt(br.readLine());
            stacktest obj=new stacktest(n);
            do
            {
            System.out.println("[1] Push [2] Pop [3] Display [4] Check stack status [5] Exit \n");
            System.out.println("Enter choice : ");
            ch=Integer.parseInt(br.readLine());
            switch(ch)
            {
                case 1:
                    System.out.println("Enter value to push : ");
                    val=Integer.parseInt(br.readLine());
                    obj.push(val);
                    obj.display();
                    break;
           
                case 2:
                    obj.pop();
                    obj.display();
                    break;
                       
                case 3:
                    obj.display();
                    break;
   
                case 4:
                    obj.check();
                    break;

                case 5:    break;

                default :
                        System.out.println("Enter correct choice..");
                        break;
            }
            }while(ch!=5);
        }
    }

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