package Queue_Java;

import java.util.*;

class ListQueue2{
    private LinkedList ll;
    private int front, rear;
    private int size;
    public ListQueue2(){
        ll = new LinkedList();
        front = -1;
        rear = -1;
        size = 0;
    }
    public boolean isEmpty(){
        return size == 0;
    }
    public void offer(Object obj){
        ll.add(obj);
        size++;
        rear++;
        if(front == -1)
            front++;
    }
    public Object peek(){
        if(isEmpty())
            return null;
        else
            return ll.get(0);
    }
    public Object element(){
        if(isEmpty())
            throw new NoSuchElementException();
        else
            return ll.get(0);
    }
    public Object poll(){
        if(isEmpty())
            return null;
        else{
            size--;
            rear--;
            if(size==0)
                front--;
            return ll.remove(0);
        }
    }
     public Object remove(){
        if(isEmpty())
            throw new NoSuchElementException();
        else{
            size--;
            rear--;
            if(size==0)
                front--;
            return ll.remove(0);
        }
    }
    
}