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"); } }
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为:
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:
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。
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:
public class Run { public static void main(String[] args){ CountOperate c = new CountOperate(); c.start(); } }
打印的log为:
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
与我们预想的结果相同