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。

class ThreadDemo extends Thread {

    private int i = 1;

    ThreadDemo(String name) {
        this.setName(name);
        System.out.println("Creating " + name);
    }

    @Override
    public void run() {
        System.out.println("Running " + this.getName());
        try {
            for (; i <= 5; i++) {
                System.out.println("Thread: " + this.getName() + " [" + i + "]");
                // 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。
                Thread.sleep((int) (Math.random() * 100));
            }
        } catch (InterruptedException e) {
            System.out.println("Thread " + this.getName() + " interrupted.");
        }
        System.out.println("Thread " + this.getName() + " exiting.");
    }

    @Override
    public void start() {
        System.out.println("Starting " + this.getName());
        super.start();
    }
}

// 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。
// 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。
public class TestThread {
    public static void main(String args[]) {
        ThreadDemo t1 = new ThreadDemo("Thread-1");
        // 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。
        t1.start();
        ThreadDemo t2 = new ThreadDemo("Thread-2");
        t2.start();
    }
}

(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。

class RunnableDemo implements Runnable {

    private int i = 1;

    RunnableDemo() {
        System.out.println("Creating" + Thread.currentThread().getName());
    }

    @Override
    public void run() {
        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.");
        }
        System.out.println("Thread " + Thread.currentThread().getName() + " exiting.");
    }
}

public class TestRunnable {

    public static void main(String args[]) {
        Runnable r1 = new RunnableDemo();
        Thread t1 = new Thread(r1);
        t1.setName("Thread-1");
        t1.start();

        Runnable r2 = new RunnableDemo();
        Thread t2 = new Thread(r2);
        t2.setName("Thread-2");
        t2.start();
    }
}

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();
        }
    }
}