java 线程 this_Java多线程之this与Thread.currentThread()的区别——java多线程编程核心技术...

蔚落 2022-11-03 11:56 187阅读 0赞

![48304ba5e6f9fe08f3fa1abda7d326ab.png][]

package mythread;

public class CountOperate extends Thread\{

public CountOperate()\{

System.out.println("CountOperate---begin");

System.out.println("Thread.currentThread().getName()=" + Thread.currentThread().getName());//获取线程名

System.out.println("Thread.currentThread().isAlive()=" + Thread.currentThread().isAlive()); //查看线程是否存活

System.out.println("this.getName=" + this.getName());

System.out.println("this.isAlive()=" + this.isAlive());

System.out.println("CountOperate---end ");

System.out.println("Thread.currentThread()==this :"+ (Thread.currentThread() == this));

@Override

public void run() \{

System.out.println("run---begin");

System.out.println("Thread.currentThread().getName=" + Thread.currentThread().getName());

System.out.println("Thread.currentThread().isAlive()" + Thread.currentThread().isAlive());

System.out.println("Thread.currentThread()==this :"+ (Thread.currentThread() == this));

System.out.println("this.getName()=" + this.getName());

System.out.println("this.isAlive()=" + this.isAlive());

System.out.println("run --- end");

![48304ba5e6f9fe08f3fa1abda7d326ab.png][]

public class Run \{

public static void main(String\[\] args)\{

CountOperate c = new CountOperate();

c.start();

Thread t1 = new Thread(c);

System.out.println("main begin t1 isAlive=" + t1.isAlive());

t1.setName("A");

t1.start();

System.out.println("main end t1 isAlive=" + t1.isAlive());

![48304ba5e6f9fe08f3fa1abda7d326ab.png][]

打印的log为:

![48304ba5e6f9fe08f3fa1abda7d326ab.png][]

CountOperate---begin

Thread.currentThread().getName()=main

Thread.currentThread().isAlive()=true

this.getName=Thread-0

this.isAlive()=false

CountOperate---end

Thread.currentThread()==this :false

main begin t1 isAlive=false

main end t1 isAlive=true

run---begin

Thread.currentThread().getName=A

Thread.currentThread().isAlive()true

Thread.currentThread()==this :false

this.getName()=Thread-0

this.isAlive()=false

run --- end

![48304ba5e6f9fe08f3fa1abda7d326ab.png][]

根据打印的Log可以知道调用CountOperate构造函数的是main线程，因此打印出

Thread.currentThread().getName()=main

Thread.currentThread().isAlive()=true

而此时还没有启动CountOperate子线程所以打印出

this.getName=Thread-0

this.isAlive()=false

此时this代表的是CountOperate对象实例，所以

Thread.currentThread()==this :false

这里比较让人疑惑的是“this.getName() = Thread-0”，这个Thread-0是什么东西？？？

通过查看Thread源码发现，在Thread类的构造方法中，会自动给name赋值，赋值代码：

![5be889331a73e33178aa7a664ab0e2a3.png][]

然后执行到:

Thread t1 = new Thread(c);

System.out.println("main begin t1 isAlive=" + t1.isAlive());

t1.setName("A");

t1.start();

Log打印：

Thread.currentThread().getName=A

Thread.currentThread().isAlive()true

Thread.currentThread()==this :false

this.getName()=Thread-0

this.isAlive()=false

说明此时的this和Thread.currentThread()指向不是同一个线程实例

也就是说，this指向的还是new CountOperate()创建的那个线程实例，而不是new Thread(thread)创建的那个实例即t1。

查看源代码可以知道。

![72a9aaf7c79116f251f363fc1a5340f8.png][]

实际上new Thread(thread)会将thread应用的对象绑定到一个pravite变量target上，

在t1被执行的时候即t1.run()被调用的时候，它会调用target.run()方法，也就是说它是直接调用thread对象的run方法，

再确切的说，在run方法被执行的时候，this.getName()实际上返回的是target.getName()，而Thread.currentThread().getName()实际上是t1.getName()。

因此我们修改下main中的代码为:

![48304ba5e6f9fe08f3fa1abda7d326ab.png][]

public class Run \{

public static void main(String\[\] args)\{

CountOperate c = new CountOperate();

c.start();

![48304ba5e6f9fe08f3fa1abda7d326ab.png][]

打印的log为:

![48304ba5e6f9fe08f3fa1abda7d326ab.png][]

CountOperate---begin

Thread.currentThread().getName()=main

Thread.currentThread().isAlive()=true

this.getName=Thread-0

this.isAlive()=false

CountOperate---end

Thread.currentThread()==this :false

run---begin

Thread.currentThread().getName=Thread-0

Thread.currentThread().isAlive()true

Thread.currentThread()==this :true

this.getName()=Thread-0

this.isAlive()=true

run --- end

![48304ba5e6f9fe08f3fa1abda7d326ab.png][]

与我们预想的结果相同

转载自：http://www.cnblogs.com/huangyichun/p/6071625.html

[48304ba5e6f9fe08f3fa1abda7d326ab.png]: /images/20221024/640e90efc9d24a67b6e508e50bae0d8b.png
[5be889331a73e33178aa7a664ab0e2a3.png]: /images/20221024/880aeb0cc37744cfbd5866c2655d9820.png
[72a9aaf7c79116f251f363fc1a5340f8.png]: /images/20221024/a8dc13a29ea14c8d8cda7766a6730c92.png