Java多线程(1)：3种常用的实现多线程类的方法
(1) 继承java.lang.Thread类(Thread也实现了Runnable接口)
继承Thread类的方法是比较常用的一种，如果说你只是想起一条线程。没有什么其它特殊的要求，那么可以使用Thread。一般推荐Runable。Thread类实际上也是实现了Runnable接口的类。
1 class ThreadDemo extends Thread { 2 3 private int i = 1; 4 5 ThreadDemo(String name) { 6 this.setName(name); 7 System.out.println("Creating " + name); 8 } 9 10 @Override11 public void run() {12 System.out.println("Running " + this.getName());13 try {14 for (; i <= 5; i++) {15 System.out.println("Thread: " + this.getName() + " [" + i + "]");16 // Thread.sleep()方法调用目的是不让当前线程独自霸占该进程所获取的CPU资源，以留出一定时间给其他线程执行的机会。17 Thread.sleep((int) (Math.random() * 100));18 }19 } catch (InterruptedException e) {20 System.out.println("Thread " + this.getName() + " interrupted.");21 }22 System.out.println("Thread " + this.getName() + " exiting.");23 }24 25 @Override26 public void start() {27 System.out.println("Starting " + this.getName());28 super.start();29 }30 }31 32 // 程序启动运行main时候，java虚拟机启动一个进程，主线程main在main()调用时候被创建。33 // 随着调用ThreadDemo的两个对象的start方法，另外两个线程也启动了，这样，整个应用就在多线程下运行。34 public class TestThread {35 public static void main(String args[]) {36 ThreadDemo t1 = new ThreadDemo("Thread-1");37 // start()方法的调用后并不是立即执行多线程代码，而是使得该线程变为可运行态（Runnable），什么时候运行是由操作系统决定的。38 t1.start();39 ThreadDemo t2 = new ThreadDemo("Thread-2");40 t2.start();41 }42 }
(2) 直接实现java.lang.Runnable接口
通过实现Runnable接口，使得该类有了多线程类的特征。run()方法是多线程程序的一个约定。所有的多线程代码都在run方法里面。
在启动的多线程的时候，需要先通过Thread类的构造方法Thread(Runnable target) 构造出对象，然后调用Thread对象的start()方法来运行多线程代码。
如果一个类继承Thread，则不适合资源共享。但是如果实现了Runable接口的话，则很容易的实现资源共享。
1 class RunnableDemo implements Runnable { 2 3 private int i = 1; 4 5 RunnableDemo() { 6 System.out.println("Creating" + Thread.currentThread().getName()); 7 } 8 9 @Override10 public void run() {11 System.out.println("Running " + Thread.currentThread().getName());12 try {13 for (; i <= 5; i++) {14 System.out.println("Thread: " + Thread.currentThread().getName() + " [" + i + "]");15 Thread.sleep((int) (Math.random() * 100));16 }17 } catch (InterruptedException e) {18 System.out.println("Thread " + Thread.currentThread().getName() + " interrupted.");19 }20 System.out.println("Thread " + Thread.currentThread().getName() + " exiting.");21 }22 }23 24 public class TestRunnable {25 26 public static void main(String args[]) {27 Runnable r1 = new RunnableDemo();28 Thread t1 = new Thread(r1);29 t1.setName("Thread-1");30 t1.start();31 32 Runnable r2 = new RunnableDemo();33 Thread t2 = new Thread(r2);34 t2.setName("Thread-2");35 t2.start();36 }37 }
package com.mycloud.demo.thread;import java.util.ArrayList;import java.util.List;import java.util.concurrent.Callable;import java.util.concurrent.ExecutionException;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Future;class CallableDemo implements Callable<String> { private int i = 1; CallableDemo() { System.out.println("Creating " + Thread.currentThread().getName()); } @Override public String call() { System.out.println("Running " + Thread.currentThread().getName()); try { for (; i <= 5; i++) { System.out.println("Thread: " + Thread.currentThread().getName() + " [" + i + "]"); Thread.sleep((int) (Math.random() * 100)); } } catch (InterruptedException e) { System.out.println("Thread " + Thread.currentThread().getName() + " interrupted."); return "failed"; } System.out.println("Thread " + Thread.currentThread().getName() + " exiting."); return "success"; }}public class TestCallable { public static void main(String args[]) { ExecutorService ex = Executors.newFixedThreadPool(5); List<Future<String>> futures = new ArrayList<>(); futures.add(ex.submit(new CallableDemo())); futures.add(ex.submit(new CallableDemo())); try { for (Future<String> future : futures) { System.out.println(future.get()); } } catch (InterruptedException | ExecutionException e) { e.printStackTrace(); } finally { ex.shutdown(); } }}
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