Packages In Java

How to save a package ? 
1. Create folder StackStack.
2. Create subfloder stack.
3. Save Sstack.java in subfolder stack.
4. Then, save StackDemo.java in folder StackStack.

//save as Sstack.java
package stack;

interface Instack
{
    void push(int element);
    void pop();
    void display();
}

public class Sstack implements Instack
{
     int n,arr[],top;
     public Sstack(int size)
     {
          n = size;
          arr = new int[n];
          top = -1;
     }

     public void push(int element)
     {
          int temp = 0;
          if(top >= (n-1))
          {
                System.out.println("\nStack is overflow");
          }
          else
          {
                top++;
               arr[top] = element;
               System.out.println("\nElement inserted: "+element);
          }
    }

    public void pop()
    {
        int temp;
        if(top == -1)
        {
            System.out.println("\nStack is underflow");
        }
        else
        {
            temp = arr[top];
            top--;
            System.out.println("\nElement Deleted: "+temp);
        }
    }

    public void display()
    {
        int i;
        if(top == -1)
        {
            System.out.println("\nStack is underflow");
        }

        for(i=0;i<=top;i++)
        {
            System.out.println("\n"+arr[i]);
        }
    }
}

//save as  StackDemo.java
import java.io.*;
import stack.*;             //importing package stack

class StackDemo
{
    public static void main(String s[]) throws Exception
    {
        int n,c,e,i;
        BufferedReader br  = new BufferedReader(new InputStreamReader(System.in));

        System.out.print("\nEnter number of elements in the array: ");
        n = Integer.parseInt(br.readLine());

        Sstack ss = new Sstack(n);
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