总结起来一句话：在Thread中调用this其实就是调用Thread私有Runnable类型的target，target是Thread类的一个属性，而Thread.currentThread()是指新New出来的实例Thread类。两个是不同的对象。实例化一个Thread的对象，都会将其赋值给Thread的私有target属性。

直接上代码：

注意代码中红色部分，就可以解释this和Thread.currentThread()的区别。实际上new Thread(Runnable)，new Thread(Runnable,String) 会将一个thread( Thread 是Runnable接口的实现类) 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target.getName()，而Thread.currentThread().getName()实际上是t1.getName()。

new Thread(Runnable）的源码

1  public Thread(Runnable target) {
2         init(null, target, "Thread-" + nextThreadNum(), 0);
3     }

 

 1 public class TestThread {
 2 
 3     public static void main(String[] args) {
 4         Bed b = new Bed();
 5         b.start();
 6         Thread t1 = new Thread(b,"B");
 7         System.out.println("main begin t1 isAlive=" + t1.isAlive());
 8 //        t1.setName("B");
 9         t1.start();
10         System.out.println("main end t1 isAlive=" + t1.isAlive());
11 
12     }
13 }
14 
15 class Bed extends Thread {
16 
17     public Bed() {
18         System.out.println("Bed Constructor---begin");
19         System.out.println("Thread.currentThread().getName()=" + Thread.currentThread().getName());// 获取线程名
20         System.out.println("Thread.currentThread().isAlive()=" + Thread.currentThread().isAlive()); // 查看线程是否存活
21         System.out.println("this.getName=" + this.getName());
22         System.out.println("this.isAlive()=" + this.isAlive());
23         System.out.println("Thread.currentThread()==this :" + (Thread.currentThread() == this));
24         System.out.println("Bed Constructor---end ");
25     }
26 
27     @Override
28     public void run() {
29         System.out.println("run---begin");
30         System.out.println("Thread.currentThread().getName=" + Thread.currentThread().getName());
31         System.out.println("Thread.currentThread().isAlive()" + Thread.currentThread().isAlive());
32         System.out.println("Thread.currentThread()==this :" + (Thread.currentThread() == this));
33         System.out.println("this.getName()=" + this.getName());
34         System.out.println("this.isAlive()=" + this.isAlive());
35         System.out.println("run --- end");
36     }
37 }

结果：

 1 Bed Constructor---begin
 2 Thread.currentThread().getName()=main
 3 Thread.currentThread().isAlive()=true
 4 this.getName=Thread-0
 5 this.isAlive()=false
 6 Thread.currentThread()==this :false
 7 Bed Constructor---end 
 8 main begin t1 isAlive=false
 9 run---begin
10 Thread.currentThread().getName=Thread-0
11 Thread.currentThread().isAlive()true
12 Thread.currentThread()==this :true
13 this.getName()=Thread-0
14 this.isAlive()=true
15 run --- end
16 main end t1 isAlive=true
17 run---begin
18 Thread.currentThread().getName=B
19 Thread.currentThread().isAlive()true
20 Thread.currentThread()==this :false
21 this.getName()=Thread-0
22 this.isAlive()=false
23 run --- end

b.start()的时候，就是调用Thread的run方法，而newThread对象的时候将其赋给target对象，如果未指定名称系统默认给target命名，target是线程类Thread的一个私有Runnable类型属性。

1     private Runnable target;

即使将target和new Thread的线程赋值一样的名称也不会出现this==Thread.currentThread()，从而说明target和new Thread()是两个不同的对象。

 1 public class TestThread {
 2 
 3     public static void main(String[] args) {
 4 
 5         Bed b = new Bed("A");
 6         b.start();
 7         Thread t1 = new Thread(b,"A");
 8         System.out.println("main begin t1 isAlive=" + t1.isAlive());
 9         t1.start();
10         System.out.println("main end t1 isAlive=" + t1.isAlive());
11 
12     }
13 
14 }

结果：

 1 Bed Constructor---begin
 2 Thread.currentThread().getName()=main
 3 Thread.currentThread().isAlive()=true
 4 this.getName=A
 5 this.isAlive()=false
 6 Thread.currentThread()==this :false
 7 Bed Constructor---end 
 8 run---begin
 9 Thread.currentThread().getName=A
10 Thread.currentThread().isAlive()true
11 Thread.currentThread()==this :true
12 this.getName()=A
13 this.isAlive()=true
14 run --- end
15 main begin t1 isAlive=false
16 main end t1 isAlive=true
17 run---begin
18 Thread.currentThread().getName=A
19 Thread.currentThread().isAlive()true
20 Thread.currentThread()==this :false
21 this.getName()=A
22 this.isAlive()=false
23 run --- end

Reference

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