Stack Using Linkedlist - Datastructure - JAVA

Program:
import java.io.*;
class Node
{
    public int data;
    public Node next;
    public Node(int x)
    {
        data=x;
    }
    public void display()
    {
        System.out.print(data+" ");
    }
}
class stacker
{
    public Node first;
    public stacker()
    {
        first=null;
    }
    public boolean isEmpty()
    {
        return(first==null);
    }
    public void push(int value)
    {
        Node newnode=new Node(value);
        newnode.next=first;
        first=newnode;
    }
    public int pop()
    {
        if(isEmpty())
         {
            System.out.println("\n Stack Empty...");
            return 0;
         }
        else
         {
            int r1=first.data;
            first=first.next;
            return r1;
         }
       
    }
    public void display()
    {
        Node current=first;
        while(current!=null)
         {
            System.out.print(" "+current.data);
            current=current.next;
         }
        System.out.println("");
    }
}
class stack_list
{
public static void main(String arg[]) throws IOException
{
    stacker a1=new stacker();
    DataInputStream x=new DataInputStream(System.in);
    System.out.print("\n\t\t<<STACK USING LINKEDLIST>>\n\nStack ready...\n\nEnter number of elements to push: ");
    int n1=Integer.parseInt(x.readLine());
    System.out.println("\nEnter elements: ");
    for(int i=0;i<n1;i++)
     {
        a1.push(Integer.parseInt(x.readLine()));
     }
    System.out.println("\nDo you want to see the stack items?\n\t1.Yes 2.No");
    switch(Integer.parseInt(x.readLine()))
    {
        case 1:
            System.out.println("\nThe current stack items:");
            a1.display();
            break;
        case 2:
        default:
            break;
    }
    System.out.println("\nEnter the number of elements to pop: ");
    int n2=Integer.parseInt(x.readLine());
    for(int i=0;i<n2;i++)
     {
        System.out.println(a1.pop()+" is poped from stack... ");
     }
    System.out.println("\nDo you want to see the stack items?\n\t1.Yes 2.No");
    switch(Integer.parseInt(x.readLine()))
    {
        case 1:
            System.out.println("\nThe current stack items:");
            a1.display();
            break;
        case 2:
        default:
            break;
    }
}
}
   
Output:
nn@linuxmint ~ $ javac stack_list.java
Note: stack_list.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
nn@linuxmint ~ $ java stack_list

        <<STACK USING LINKEDLIST>>

Stack ready...

Enter number of elements to push: 3

Enter elements: 
1
2
3

Do you want to see the stack items?
    1.Yes 2.No
1

The current stack items:
 3 2 1

Enter the number of elements to pop: 
1
3 is poped from stack... 

Do you want to see the stack items?
    1.Yes 2.No
1

The current stack content:
 2 1
nn@linuxmint ~ $