Java多线程使用案例【附可运行代码】

标题Java多线程使用案例

1、创建线程池，创建任务，将任务提交到线程池中执行

public class Test1 {private static Map<String, String> map = new ConcurrentHashMap<>();private static CountDownLatch countDownLatch = new CountDownLatch(4);public static void main(String[] args) {ExecutorService es = Executors.newFixedThreadPool(4);es.submit(new Task1());es.submit(new Task2());es.submit(new Task3());es.submit(new Task4());es.shutdown();System.out.println(map);}static class Task1 implements Runnable{@Overridepublic void run() {map.put("1", "1");System.out.println("我是任务1");}}static class Task2 implements Runnable{@Overridepublic void run() {map.put("2", "2");System.out.println("我是任务2");}}static class Task3 implements Runnable{@Overridepublic void run() {map.put("3", "3");System.out.println("我是任务3");}}static class Task4 implements Runnable{@Overridepublic void run() {map.put("4", "4");System.out.println("我是任务4");}}
}

结果：顺序的

2、模拟程序执行耗时–系统睡眠一段时间

public class Test1 {private static Map<String, String> map = new ConcurrentHashMap<>();private static CountDownLatch countDownLatch = new CountDownLatch(4);public static void main(String[] args) {ExecutorService es = Executors.newFixedThreadPool(4);es.submit(new Task1());es.submit(new Task2());es.submit(new Task3());es.submit(new Task4());es.shutdown();System.out.println(map);}static class Task1 implements Runnable{@Overridepublic void run() {try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}map.put("1", "1");System.out.println("我是任务1");}}static class Task2 implements Runnable{@Overridepublic void run() {try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}map.put("2", "2");System.out.println("我是任务2");}}static class Task3 implements Runnable{@Overridepublic void run() {try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}map.put("3", "3");System.out.println("我是任务3");}}static class Task4 implements Runnable{@Overridepublic void run() {try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}map.put("4", "4");System.out.println("我是任务4");}}
}

此时的执行顺序，发现主线程没有等待任务执行完就先执行了打印的结果为空

3、增加计数器，等待线程执行完主线程才往下执行

public class Test1 {private static Map<String, String> map = new ConcurrentHashMap<>();private static CountDownLatch countDownLatch = new CountDownLatch(4);public static void main(String[] args) {ExecutorService es = Executors.newFixedThreadPool(4);es.submit(new Task1());es.submit(new Task2());es.submit(new Task3());es.submit(new Task4());es.shutdown();try {countDownLatch.await();} catch (InterruptedException e) {e.printStackTrace();}System.out.println(map);}static class Task1 implements Runnable{@Overridepublic void run() {try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}map.put("1", "1");System.out.println("我是任务1");countDownLatch.countDown();}}static class Task2 implements Runnable{@Overridepublic void run() {try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}map.put("2", "2");System.out.println("我是任务2");countDownLatch.countDown();}}static class Task3 implements Runnable{@Overridepublic void run() {try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}map.put("3", "3");System.out.println("我是任务3");countDownLatch.countDown();}}static class Task4 implements Runnable{@Overridepublic void run() {try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}map.put("4", "4");System.out.println("我是任务4");countDownLatch.countDown();}}
}

注意类的加载机制

实际使用的时候，如果需要成员变量共享，应该在方法里面实例化对象，在类里面初始化对象

否则执行的时候会出现问题，实际访问的对象是上次的。

多线程具有短板效应，最终的效率取决于效率最慢的那一个任务

这里定义4个线程会有4个线程同时处理这四个任务

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