循环队列

循环队列：为了将顺序队列底层数组中已删除元素所占用的空间重新利用，消除可能出现的“假满”现象。

package MyJava2;

import java.util.Arrays;

public class LoopQueue {
    private int DEFAULT_SIZE=10;
    private int capacity;
    private String[] elelments;
    private int front=0;
    private int rear=0;

    public LoopQueue(){
        capacity=DEFAULT_SIZE;
        elelments=new String[capacity];
    }
    public LoopQueue(String data){
        capacity=DEFAULT_SIZE;
        elelments=new String[capacity];
        elelments[0]=data;
        rear++;
    }
    public LoopQueue(String data,int initionalize){
        capacity=1;
        while (capacity<initionalize){
            capacity<<=1;
        }
        elelments=new String[capacity];
        elelments[0]=data;
        rear++;
    }

    public int len(){
        if(empty()){
            return 0;
        }else {
            return rear>front?rear-front:capacity-(front-rear);
        }
    }

    public void add(String data){
        if(rear==front&&elelments[rear]!=null){
            throw new IndexOutOfBoundsException("队列已满");
        }
        elelments[rear++]=data;
        rear=rear==capacity?0:rear;//如果rear已经到头，则转头
    }
    public String remove(){
        if (empty()){
            throw new IndexOutOfBoundsException("队列为空");
        }
        String old=elelments[front];
        elelments[front++]=null;
        front=front==capacity?0:front;//若front到头，则转头
        return old;
    }
    public String getFront(){
        if (empty()){
            throw new IndexOutOfBoundsException("队列为空");
        }
        return elelments[front];
    }

    public boolean empty() {
        return rear==front&&elelments[rear]==null;
    }
    public void clear(){
        Arrays.fill(elelments,null);
        front=0;
        rear=0;
    }

    public String toString(){
        if(front<rear){//有效元素为front到rear之间的元素
            StringBuffer sb=new StringBuffer();
            for(int i=front;i<rear;i++){
                sb.append(elelments[i].toString()+",");
            }return sb.toString();
        }else {//front>=rear,有效元素为front->capacity和0->rear之间的元素
            StringBuffer sb=new StringBuffer();
            for(int i=front;i<capacity;i++){
                sb.append(elelments[i].toString()+",");
            }
            for(int i=0;i<rear;i++){
                sb.append(elelments[i].toString()+",");
            }return sb.toString();
        }
    }

    public static void main(String[] args) {
        LoopQueue queue=new LoopQueue("A",3);
        queue.add("B");
        queue.add("C");
        System.out.println(queue.toString());
        System.out.println(queue.len());
        queue.remove();
        queue.add("A1");
        System.out.println(queue.toString());
        System.out.println(queue.len());
    }
}