Java多线程之CountDownLatch用法

Dear 丶 2022-02-01 08:11 381阅读 0赞

# Java多线程之CountDownLatch用法 #

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## 本文目录： ##

1.  CountDownLatch基本概念
2.  CountDownLatch案例：6个同学陆续离开教室后班长才可以关门
3.  CountDownLatch案例：秦灭6国，一统华夏

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### 1. CountDownLatch基本概念 ###

##### `1. 让一些线程阻塞直到另一些线程完成一系列操作后才被唤醒。` #####

##### `2. CountDownLatch主要有两个方法，当一个或多个线程调用await方法时，这些线程会阻塞。其它线程调用countDown方法会将计数器减1(调用countDown方法的线程不会阻塞)，当计数器的值变为0时，因await方法阻塞的线程会被唤醒，继续执行。` #####

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### 2. CountDownLatch案例：6个同学陆续离开教室后班长才可以关门 ###

**实现：**

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**编译结果**  
![在这里插入图片描述][20190513213740299.png]

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### 3. CountDownLatch案例：秦灭6国，一统华夏 ###

1.  六国我们用枚举模拟，具体代码如下：

public enum CountryEnums {
        
        ONE(1,"韩"),TWO(2,"魏"),THREE(3,"赵"),FOUR(4,"齐"),FIVE(5,"楚"),SIX(6,"燕");
    
        private Integer retCode;
        private String retMessage;
    
        CountryEnums(Integer retCode, String retMessage) {
        
            this.retCode = retCode;
            this.retMessage = retMessage;
        }
    
        public Integer getRetCode() {
        
            return retCode;
        }
    
        public void setRetCode(Integer retCode) {
        
            this.retCode = retCode;
        }
    
        public String getRetMessage() {
        
            return retMessage;
        }
    
        public void setRetMessage(String retMessage) {
        
            this.retMessage = retMessage;
        }
    
        public static CountryEnums forEachCountryEnums(Integer index){
        
            for (CountryEnums element: values()) {
        
                if (element.getRetCode() == index){
        
                    return element;
                }
            }
            return null;
        }
    }

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**主体代码：**

public class CountDownLatchDemo {
        
        public static void main(String[] args) throws InterruptedException {
        
            CountDownLatch countDownLatch = new CountDownLatch(6);
            for (int i = 1; i <=6 ; i++) {
        
                new Thread(() -> {
        
                    System.out.println(Thread.currentThread().getName()+"\t 国被灭亡");
                    countDownLatch.countDown();
                },CountryEnums.forEachCountryEnums(i).getRetMessage()).start();
    
            }
            countDownLatch.await();
            System.out.println(Thread.currentThread().getName()+"\t 秦，统一华夏");
    
    		System.out.println("------------------");
    
    		//枚举测试代码
            System.out.println(CountryEnums.ONE);
            System.out.println(CountryEnums.ONE.getRetCode());
            System.out.println(CountryEnums.ONE.getRetMessage());
    
        }

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**编译结果：**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MTkxMDY5NA_size_16_color_FFFFFF_t_70]

[20190513213740299.png]: /images/20220201/4dff5437c39441c3aeb027db799dc78e.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MTkxMDY5NA_size_16_color_FFFFFF_t_70]: /images/20220201/616db9d48f0947f49c2247f557b592fe.png