队列

AbstractQueue类

public abstract class AbstractQueue<E> {
    public abstract void push(E e);
    public abstract void pop();
    public abstract E front();
}

用顺序表实现队列

public class ArrayQueue<E> extends AbstractQueue<E>{

    private Object[] arr=new Object[4];
    private int front=0,rear=0;

    @Override
    public void push(E e) {
        if((rear+1)%arr.length==front) throw new IndexOutOfBoundsException("超出队列长度！");
        arr[rear]=e;
        rear=(rear+1)%arr.length;
    }

    @Override
    public void pop() {
        if(front==rear)throw new IllegalArgumentException("没有元素在队列中！");
        arr[front]=null;
        front=(front+1)% arr.length;
    }

    @Override
    public E front() {
        if(front==rear)throw new IllegalArgumentException("没有元素在队列中！");
        return (E) arr[front];
    }
}