队列介绍
- 队列是一个有序列表,可以用数组或是链表来实现。
- 遵循先入先出规则,即,先入队列的数据,要先取出。后存入的要后取出。
数组模拟队列
- 如下图所示
- 因为队列的输出、输入是分别从前后端来处理的,因此需要两个变量front、rear分别记录队列前后端的下标。front会随着数据输出而改变,rear会随着数据输入而改变。
- 很致命的问题是,当rear=maxSize-1时,无论front在哪个位置,程序都会提醒“队列满”
代码实现
import java.util.Scanner;
class ArrayQueueDemo{
public static void main(String[] args){
ArrayQueue arrayQueue = new ArrayQueue(3);
Scanner scanner = new Scanner(System.in);
char key = ' ';
boolean loop = true;
while(loop){
System.out.println("s(show)");
System.out.println("a(add)");
System.out.println("g(get)");
System.out.println("e(exit)");
System.out.println("h(head)");
key = scanner.next().charAt(0);
switch(key){
case 's':
arrayQueue.showQueue();
break;
case 'a':
System.out.println("请输入一个数");
try {
int temp1 = scanner.nextInt();
arrayQueue.addQueue(temp1);
}catch(Exception e){
e.printStackTrace();
}
break;
case 'g':
try{
System.out.println(arrayQueue.getQueue());
}catch(Exception e){
e.printStackTrace();
}
break;
case 'e':
loop = false;
break;
case 'h':
System.out.println(arrayQueue.headQueue());
break;
default:
break;
}
}
System.out.println("退出程序");
}
}
class ArrayQueue {
private int maxSize;
private int front;
private int rear;
private int[] arr;
public ArrayQueue(int maxSize){
this.maxSize = maxSize;
front = -1;
rear = -1;
arr = new int[maxSize];
}
public boolean isFull(){
return rear == maxSize - 1;
}
public boolean isEmpty(){
return rear == front;
}
public void addQueue(int n){
if(isFull()){
System.out.println("队列满");
return;
}
rear++;
arr[rear] = n;
}
public int getQueue(){
if(isEmpty()){
throw new RuntimeException("队列空");
}
front++;
return arr[front];
}
public int headQueue(){
if(isEmpty()){
throw new RuntimeException("队列空");
}
return arr[front+1];
}
public void showQueue(){
if(isEmpty()){
System.out.println("队列空");
return;
}
for(int i = front + 1; i <= rear; i++){
System.out.printf("%d\t", arr[i]);
}
System.out.println();
}
}