Design a Java interface for Stack ADT and Implement it using Array and Linked List

Design a Java interface for Stack ADT and develop two different classes that implements this interface, one using array and the other using linked list.

import java.io.*;
interface Mystack
{
    public void pop();
    public void push();
    public void display();
}
class Stack_array implements Mystack
{
    final static int n=5;
    int stack[]=new int[n];
    int top=-1;
    public void push()
    {
        try
        {
            BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
            if(top==(n-1))
            {
                System.out.println(" Stack Overflow");
                return;
            }
            else
            {
                System.out.println("Enter the element");
                int ele=Integer.parseInt(br.readLine());
                stack[++top]=ele;
            }
        }
        catch(IOException e)
        {
            System.out.println("e");
        }
    }
    public void pop()
    {
        if(top<0)
        {
            System.out.println("Stack underflow");
            return;
        }
        else
        {
            int popper=stack[top];
            top--;
            System.out.println("Popped element:" +popper);
        }
    }

    public void display()
    {
        if(top<0)
        {
            System.out.println("Stack is empty");
            return;
        }
        else
        {
            String str=" ";
            for(int i=0; i<=top; i++)
                str=str+"  "+stack[i]+" <--";
            System.out.println("Elements are:"+str);
        }
    }
}
class Link
{
    public int data;
    public Link nextLink;
    public Link(int d)
    {
        data= d;
        nextLink=null;
    }
    public void printLink()
    {
        System.out.print(" --> "+data);
    }
}
class Stack_List  implements Mystack
{
    private Link first;
    public Stack_List()
    {
        first = null;
    }
    public boolean isEmpty()
    {
        return first == null;
    }
    public void push()
    {
        try
        {
            BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
            System.out.println("Enter the element");
            int ele=Integer.parseInt(br.readLine());
            Link link = new Link(ele);
            link.nextLink = first;
            first = link;
        }
        catch(IOException e)
        {
            System.err.println(e);
        }
    }
    public Link delete()
    {
        Link temp = first;
        try
        {
            first = first.nextLink;
        }
        catch(NullPointerException e)
        {
            throw e;
        }
        return temp;
    }
    public void pop()
    {
        try
        {
            Link deletedLink = delete();
            System.out.println("Popped: "+deletedLink.data);
        }
        catch(NullPointerException e)
        {
            throw e;
        }
    }
    public void display()
    {
        if(first==null)
            System.out.println("Stack is empty");
        else
        {
            Link currentLink = first;
            System.out.print("Elements are: ");
            while(currentLink != null)
            {
                currentLink.printLink();
                currentLink = currentLink.nextLink;
            }
            System.out.println("");
        }
    }
}
class StackADT
{
    public static void main(String arg[])throws IOException
    {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        System.out.println("Implementation of Stack using Array");
        Stack_array stk=new Stack_array();
        int ch=0;
        do
        {
            System.out.println("1.Push 2.Pop 3.Display 4.Exit 5.Use Linked List");
            System.out.println("Enter your choice:");
            ch=Integer.parseInt(br.readLine());
            switch(ch)
            {
            case 1:
                stk.push();
                break;
            case 2:
                stk.pop();
                break;
            case 3:
                stk.display();
                break;
            case 4:
            	System.exit(0);
            }
        }
        while(ch<5);
        System.out.println("Implementation of Stack using Linked List");
        Stack_List stk1=new Stack_List();
        ch=0;
        do
        {
            System.out.println("1.Push 2.Pop 3.Display 4.Exit");
            System.out.println("Enter your choice:");
            ch=Integer.parseInt(br.readLine());
            switch(ch)
            {
            case 1:
                stk1.push();
                break;
            case 2:
                try
                {
                    stk1.pop();
                }
                catch(NullPointerException e)
                {
                    System.out.println("Stack underflown");
                }
                break;
            case 3:
                stk1.display();
                break;
            default:
            	System.exit(0);
                
            }
        }
        while(ch<5);
    }
}

OUTPUT:

Implementation of Stack using Array
1.Push 2.Pop 3.Display 4.Exit 5.Use Linked List
Enter your choice:
1
Enter the element
10
1.Push 2.Pop 3.Display 4.Exit 5.Use Linked List
Enter your choice:
1
Enter the element
15
1.Push 2.Pop 3.Display 4.Exit 5.Use Linked List
Enter your choice:
1
Enter the element
25
1.Push 2.Pop 3.Display 4.Exit 5.Use Linked List
Enter your choice:
3
Elements are:   10 <--  15 <--  25 <--
1.Push 2.Pop 3.Display 4.Exit 5.Use Linked List
Enter your choice:
5
Implementation of Stack using Linked List
1.Push 2.Pop 3.Display 4.Exit
Enter your choice:
1
Enter the element
10
1.Push 2.Pop 3.Display 4.Exit
Enter your choice:
1
Enter the element
15
1.Push 2.Pop 3.Display 4.Exit
Enter your choice:
1
Enter the element
20
1.Push 2.Pop 3.Display 4.Exit
Enter your choice:
3
Elements are:  --> 20 --> 15 --> 10
1.Push 2.Pop 3.Display 4.Exit
Enter your choice:
2
Popped: 20
1.Push 2.Pop 3.Display 4.Exit
Enter your choice:
3
Elements are:  --> 15 --> 10
1.Push 2.Pop 3.Display 4.Exit
Enter your choice:
4