Java 实现多线程的三种方式

import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;

public class Main {

    public static void main(String[] args) {
        //方法一：继承Thread
        int i = 0;
//        for(; i < 100; i++){
//            System.out.println(Thread.currentThread().getName() + " " + i);
//            if (i == 5) {
//                ThreadExtendsThread threadExtendsThread = new ThreadExtendsThread();
//                threadExtendsThread.start();
//            }
//        }
        
        //方法二：实现Runnable
//        for(i = 0; i < 100; i++){
//            System.out.println(Thread.currentThread().getName() + " " + i);
//            if (i == 5) {
//                Runnable runnable = new ThreadImplementsRunnable();
//                new Thread(runnable).start();
//                new Thread(runnable).start();
//            }
//        }

        //方法三：实现Callable接口
        Callable<Integer> callable = new ThreadImplementsCallable();
        FutureTask<Integer> futureTask = new FutureTask<>(callable);
        for(i = 0; i < 100; i++){
            System.out.println(Thread.currentThread().getName() + " " + i);
            if (i == 5) {
                new Thread(futureTask).start();
                new Thread(futureTask).start();
            }
        }
        try {
            System.out.println("futureTask ruturn: " + futureTask.get());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

方法一，继承自Thread

public class ThreadExtendsThread extends Thread {
    private int i;
    @Override
    public void run() {
        for(; i < 100; i++) {
            System.out.println(getName() + " " + i); 
        }
    }
}

run方法为线程执行体，ThreadExtendsThread对象即为线程对象。

方法二，实现Runnable接口

public class ThreadImplementsRunnable implements Runnable {
    private int i;
    @Override
    public void run() {
        for(; i < 100; i++){
            System.out.println(Thread.currentThread().getName() + " " + i);
        }
    }
}

run方法为线程执行体，使用时New一个Thread对象，Runnable对象作为target传递给Thread对象。且同一个Runnable对象可作为多个Thread的target，这些线程均共享Runnable对象的实例变量。

方法三，实现Callable接口

import java.util.concurrent.Callable;

public class ThreadImplementsCallable implements Callable<Integer> {
    private int i;
    
    @Override
    public Integer call() throws Exception {
        for(; i < 100; i++){
            System.out.println(Thread.currentThread().getName() + " " + i);
        }
        return i;
    }
}

Callable接口类似于Runnable接口，但比对方强大，线程执行体为call方法，该方法具有返回值和可抛出异常。使用时将Callable对象包装为FutureTask对象，通过泛型指定返回值类型。可稍候调用FutureTask的get方法取回执行结果。