Java 多線程 ---- 線程中this與 Thread.currentThread()線程的區別

總結起來一句話：在Thread中調用this其實就是調用Thread私有Runnable類型的target，target是Thread類的一個屬性，而Thread.currentThread()是指新New出來的實例Thread類。兩個是不同的對象。實例化一個Thread的對象，都會將其賦值給Thread的私有target屬性。

直接上代碼：

注意代碼中紅色部分，就可以解釋this和Thread.currentThread()的區別。實際上new Thread(Runnable)，new Thread(Runnable,String) 會將一個thread( Thread 是Runnable接口的實現類) 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target.getName()，而Thread.currentThread().getName()實際上是t1.getName()。

new Thread(Runnable）的源碼

 public Thread(Runnable target) {
        init(null, target, "Thread-" + nextThreadNum(), 0);
    }

 

public class TestThread {

    public static void main(String[] args) {
        Bed b = new Bed();
 5         b.start();
 6         Thread t1 = new Thread(b,"B");
        System.out.println("main begin t1 isAlive=" + t1.isAlive());
//        t1.setName("B");
        t1.start();
        System.out.println("main end t1 isAlive=" + t1.isAlive());

    }
}

class Bed extends Thread {

    public Bed() {
        System.out.println("Bed Constructor---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("Thread.currentThread()==this :" + (Thread.currentThread() == this));
        System.out.println("Bed Constructor---end ");
    }

    @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");
    }
}

結果：

Bed Constructor---begin
Thread.currentThread().getName()=main
Thread.currentThread().isAlive()=true
this.getName=Thread-0
this.isAlive()=false
Thread.currentThread()==this :false
Bed Constructor---end 
main begin t1 isAlive=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
main end t1 isAlive=true
run---begin
Thread.currentThread().getName=B
Thread.currentThread().isAlive()true
Thread.currentThread()==this :false
this.getName()=Thread-0
this.isAlive()=false
run --- end

b.start()的時候，就是調用Thread的run方法，而newThread對象的時候將其賦給target對象，如果未指定名稱系統默認給target命名，target是線程類Thread的一個私有Runnable類型屬性。

    private Runnable target;

即使將target和new Thread的線程賦值一樣的名稱也不會出現this==Thread.currentThread()，從而說明target和new Thread()是兩個不同的對象。

public class TestThread {

    public static void main(String[] args) {

        Bed b = new Bed("A");
        b.start();
        Thread t1 = new Thread(b,"A");
        System.out.println("main begin t1 isAlive=" + t1.isAlive());
        t1.start();
        System.out.println("main end t1 isAlive=" + t1.isAlive());

    }

}

結果：

Bed Constructor---begin
Thread.currentThread().getName()=main
Thread.currentThread().isAlive()=true
this.getName=A
this.isAlive()=false
Thread.currentThread()==this :false
Bed Constructor---end 
run---begin
Thread.currentThread().getName=A
Thread.currentThread().isAlive()true
Thread.currentThread()==this :true
this.getName()=A
this.isAlive()=true
run --- end
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()=A
this.isAlive()=false
run --- end

Reference

[1] https://www.cnblogs.com/huangyichun/p/6071625.html