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



    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





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  • 原文地址:https://www.cnblogs.com/huangyichun/p/6071625.html
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