Princeton1/module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayQueue.java

package com.hithomelabs.princeton1.module4;

import java.util.Iterator;

public class ArrayQueue<Item> extends Queue<Item> {

    private int capacity=3;
    private Item[] arr = (Item[]) new Object[capacity];
    private int head=0,tail=0;

    @Override
    public boolean isEmpty() {
        return (tail - head) == 0;
    }

    private void resize(int newCapacity){
        Item[] temp = arr;
        arr = (Item[]) new Object[newCapacity];
        int iNew=0,iOld=head;
        while(iOld<tail){
            arr[iNew]=temp[iOld];
            iNew++;
            iOld++;
        }

        capacity=newCapacity;
    }

    @Override
    public Item dequeue() {
        if(isEmpty())
            return null;
        //        System.out.println(head+" "+arr[head]);
        Item element = arr[head++];
        if(size() < capacity/4)
            resize(capacity/2);
        return element;
    }

    @Override
    public void enqueue(Item element) {
        if(tail == capacity)
            resize(capacity * 2);
        arr[tail++] = element;
    }

    @Override
    public int size() {
        return (tail - head);
    }

    @Override
    public Iterator<Item> iterator() {
        return new Iterator<Item>() {
            int current = head;
            @Override
            public boolean hasNext() {
                return current != tail;
            }

            @Override
            public Item next() {
                return arr[current++];
            }
        };
    }
}