Java 多线程学习笔记3

今天简单记录一下多线程里面的几个方法

1 currentThread currentThread 方法可以返回当前代码段正在被哪个线程调用信息

package smaug.cloud.provider.thread.t2;

/**
 * Created by naonao on 17/12/9.
 */
public class MyThread implements Runnable {
    public MyThread() {
        System.out.println("当前线程名字" + Thread.currentThread().getName() + "  ");
    }

    @Override
    public void run() {
        System.out.println("当前线程名字" + Thread.currentThread().getName());
    }
}

package smaug.cloud.provider.thread.t2;

/**
 * Created by naonao on 17/12/9.
 */
public class MyTest {
    public static void main(String[] args) {
        MyThread myThread = new MyThread();
        Thread t = new Thread(myThread, "A");
        t.start();
    }
}

输出

当前线程名字main  
当前线程名字A

但是如果代码稍微改一下就像下面这样

public class MyTest {
    public static void main(String[] args) {
        MyThread myThread = new MyThread();
        Thread t = new Thread(myThread, "A");
        //t.start();
        t.run();
    }
}
输出是啥nie
当前线程名字main  
当前线程名字main

再次验证了run 方法只是个普通的方法，如果要创建线程必须用start

在写一个稍微复杂的例子

package smaug.cloud.provider.thread.t2;

/**
 * Created by naonao on 17/12/9.
 */
public class MyThread2 extends Thread {
    public MyThread2() {
        System.out.println("MyThread  begin --------");
        System.out.println("Thread.currentThread().getName() " + Thread.currentThread().getName());
        System.out.println("this.getName() " + this.getName());
        System.out.println("MyThread  end --------");
    }

    @Override
    public void run() {
        System.out.println("run  begin --------");
        System.out.println("Thread.currentThread().getName() " + Thread.currentThread().getName());
        System.out.println("this.getName() " + this.getName());
        System.out.println("run  end --------");
    }
}

输出

MyThread  begin --------
Thread.currentThread().getName() main
this.getName() Thread-0
MyThread  end --------
run  begin --------
Thread.currentThread().getName() bab
this.getName() bab
run  end --------

2.isAlive 判断线程是否存活也就是是否还在运行

package smaug.cloud.provider.thread.t3;

/**
 * Created by naonao on 17/12/9.
 */
public class MyThread extends Thread {
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + " isAlive " +this.isAlive());
    }
}

package smaug.cloud.provider.thread.t3;

/**
 * Created by naonao on 17/12/9.
 */
public class MyTest {
    public static void main(String[] args) {
        MyThread myThread = new MyThread();
        System.out.println("myThread is alive " + myThread.isAlive());
        myThread.start();
        System.out.println("myThread is alive " + myThread.isAlive());
    }
}

得到的输出

myThread is alive false
Thread-0 isAlive true
myThread is alive false

3 sleep sleep方法是让当前线程休眠一段时间

package smaug.cloud.provider.thread.t4;

/**
 * Created by naonao on 17/12/9.
 */
public class MyThread implements Runnable {
    @Override
    public void run() {
        try {
            System.out.println("begin " + System.currentTimeMillis());
            Thread.sleep(2000);
            System.out.println("end   " + System.currentTimeMillis());
        } catch (InterruptedException e) {

        }
    }
}

package smaug.cloud.provider.thread.t4;

/**
 * Created by naonao on 17/12/9.
 */
public class MyTest {
    public static void main(String[] args) {
        MyThread myThread = new MyThread();
        Thread t = new Thread(myThread);
        t.start();
    }
}

从输出时间来看，它睡着了两秒钟

begin 1512820680346
end   1512820682351

Java 多线程学习笔记3

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