Java program to implement Queue using Package and Interface

/* Queue.java */
package mypack;

import java.io.*;
interface Queue1
{
 public void initialize();
 public void insQueue();
 public void delQueue();
 public void display();
 
 BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
}

public class Queue implements Queue1
{
 private int Q[];
 private int size;
 private int front;
 private int rear;
 
 public void initialize()
 {
  try
  {
   front=-1;
   rear=-1;
   
   System.out.print("Enter size of the queue: ");
   size=Integer.parseInt(br.readLine());
   Q=new int[size];
  }
  catch(Exception e)
  {
   System.err.println(e);
  }
 }
 
 public void insQueue()
 {
  if(rear==size-1)
   System.out.println("\tQueue overflow");
  else
  {
   try
   {
    System.out.print("\tEnter data to insert: ");
    Q[++rear]=Integer.parseInt(br.readLine());
   }
   catch(Exception e)
   {
    System.err.println(e);
   }
  }
 }
 
 public void delQueue()
 {
  if(front==rear)
   System.out.println("\tQueue underflow");
  else
   System.out.println("\tDeleted item is: "+Q[++front]);
 }
 
 public void display()
 {
  if(front==rear)
   System.out.println("\tQueue is empty");
  else
  {
   System.out.print("\tQueue items are: ");
   for(int i=front+1;i<=rear;i++)
    System.out.print("\t"+Q[i]);
   System.out.println();
  }
 }
}

After compiling above code, "Queue.class" & "Queue1.class" files will be generated. Create a new folder and name it as "mypack" in the same location of your program and copy the "Queue.class" & "Queue1.class" files in the folder.

Place the below code outside "mypack" and run it

/* Test.java */
import mypack.Queue;
import java.io.*;
class Main
{
 public static void main(String[] args)
 {
  BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
  Queue ob=new Queue();
  ob.initialize();
  try
  {
   int exit=0;
   while(exit==0)
   {
    System.out.println("1.Insert\t2.Delete\t3.DISPLAY\t4.EXIT");
    System.out.print("\tEnter your choice: ");
    int ch=Integer.parseInt(br.readLine());
    
    switch(ch)
    {
        case 1:ob.insQueue();
               break;
        case 2:ob.delQueue();
               break;
        case 3:ob.display();
               break;
        case 4:exit=1;
            break;
        default:System.out.println("Wrong choice given");
    }
   }
  }
  catch(Exception e)
  {
   System.err.println(e);
  }
 }
}

Output