Java多線程之this與Thread.currentThread()的區別——java多線程編程核心技術

package mythread;

public class CountOperate extends Thread{

    public CountOperate(){
        System.out.println("CountOperate---begin");
        System.out.println("Thread.currentThread().getName()=" + Thread.currentThread().getName());//獲取線程名
        System.out.println("Thread.currentThread().isAlive()=" + Thread.currentThread().isAlive()); //查看線程是否存活
        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");
    }
}

 
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());

    }
}

打印的log為:

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

根據打印的Log可以知道調用CountOperate構造函數的是main線程，因此打印出

Thread.currentThread().getName()=main
Thread.currentThread().isAlive()=true
而此時還沒有啟動CountOperate子線程所以打印出

this.getName=Thread-0
this.isAlive()=false

此時this代表的是CountOperate對象實例，所以

Thread.currentThread()==this :false

這里比較讓人疑惑的是“this.getName() = Thread-0”，這個Thread-0是什么東西？？？ 

通過查看Thread源碼發現，在Thread類的構造方法中，會自動給name賦值，賦值代碼：

然后執行到:

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
說明此時的this和Thread.currentThread()指向不是同一個線程實例

也就是說，this指向的還是new CountOperate()創建的那個線程實例，而不是new Thread(thread)創建的那個實例即t1。
查看源代碼可以知道。

實際上new Thread(thread)會將thread應用的對象綁定到一個pravite變量target上，
在t1被執行的時候即t1.run()被調用的時候，它會調用target.run()方法，也就是說它是直接調用thread對象的run方法，
再確切的說，在run方法被執行的時候，this.getName()實際上返回的是target.getName()，而Thread.currentThread().getName()實際上是t1.getName()。

因此我們修改下main中的代碼為:

public class Run {

    public static void main(String[] args){

        CountOperate c = new CountOperate();
        c.start();
    }
}

打印的log為:

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

與我們預想的結果相同