LoopQueue.java

public class LoopQueue<E> implements Queue<E> {
	private E[] data;
	private int front,tail;
	private int size;
	
	public 	LoopQueue(int capacity) {
		data=(E[])new Object[capacity+1];
		front=0;
		tail=0;
		size=0;
	}
	public LoopQueue() {
		this(10);
	}
	public int getCapacity() {
		return data.length-1;
	}
	@Override
	public boolean isEmpty() {
		return front==tail;
	}
	@Override
	public int getSize() {
		return size;
	}
	@Override
	public void enqueue(E e) {
		if((tail+1)%data.length==front) {
			resize(getCapacity()*2);
		}
		data[tail]=e;
		tail=(tail+1)%data.length;
		size++;
	}
	@Override
	public E dequeue() {
		if(isEmpty()) {
			throw new IllegalArgumentException("queue is empty");
		}
		E ret =data[front];
		data[front]=null;
		front=(front+1)%data.length;
		size--;
		if(size==getCapacity()/4&&getCapacity()/2!=0) {
			resize(getCapacity()/2);
		}
		return ret;
	}
	@Override
	public E getFront() {
		if(isEmpty()) {
			throw new IllegalArgumentException("queue is empty");
		}
		return data[front];
	}
	
	public void resize(int newCapacity) {
		E[] newData=(E[])new Object[newCapacity+1];
		for(int i=0;i<size;i++) {
			newData[i]=data[(i+front)%data.length];
		}
		data=newData;
		front=0;
		tail=size;
	}
	@Override
	public String toString() {
		StringBuilder res=new StringBuilder();
		res.append(String.format("queue:size =%d,capacity=%d\n", size,getCapacity()));
		res.append("front [");
		for(int i=front;i!=tail;i=(i+1)%data.length) {
			res.append(data[i]);
			if((i+1)%data.length!=tail) {
				res.append(",");
			}
		}
		res.append("] tail");
		return res.toString();
	}
	public static void main(String[] args) {
		LoopQueue<Integer> queue =new LoopQueue<>();
		for(int i=0;i<10;i++) {
			queue.enqueue(i);
			System.out.println(queue);
			if(i%3==2) {
				queue.dequeue();
				System.out.println(queue);
			}
		}
	}
}