为什么我从此Java程序获取以下输出？

Question

class MyThread extends Thread 
{
    MyThread() 
    {
        System.out.print(" MyThread");
    }
    public void run() 
    {
        System.out.print(" bar");
    }
    public void run(String s) 
    {
        System.out.println(" baz");
    }
}
public class TestThreads 
{
    public static void main (String [] args) 
    {
        Thread t = new MyThread() 
        {
            public void run() 
            {
                System.out.println(" foo");
            }
        };
        t.start();
    }
}

Hello, I am new in java and currently learning Multithreading, When I am running the above program then i am getting this particular output MyThread foo please explain why?

Answer 1

MyThread comes from the constructor

foo comes from the run method which gets called when start() is called .

Essentially the run() method (which prints baz ) is overridden in your main .

and the run(String s) is an overloaded method which has no significance here.

Answer 2

It is executing the MyThread constructor and then executing the run() method .

Thread t = new MyThread() , you are trying to create a MyThread object and hence it executes the constructor.

MyThread() 
{
    System.out.print(" MyThread");
}

Then you start the thread t.start(); , it executes the run() method which you have overridden in main(String[] args) :

public void run() 
{
     System.out.println(" foo");
}

Answer 3

You first create an instance of MyThread , which calls the constructor and prints " MyThread". Then, you call t.start(); which calls the run method.

Even though you defined a run method printing " bar", it is overriden by the one in the main method (that prints " foo").

Try the following:

Thread t = new MyThread();
t.start();

And see what happens!

Answer 4

The reason is that first when create object is invoked constructor MyThread and print first part of string. When you start thread, execution continue with run method and print foo .

Answer 5

The first output inside the default constructor of MyThread , and it overrides a run() method:

Thread t = new MyThread() 
        {
            public void run() 
            {
                System.out.println(" foo");
            }
        };

Output:

Thread foo

Thread t = new MyThread() ;

Output:

MyThread bar

Note that first one you overrode the run() method and used your custom message inside it, but the second will override run() by default in MyThread class.

Answer 6

You are overriding the run method when you create Thread t . This new implementation prints " foo", which takes priority over the one you implemented in your class MyThread which still runs its own constructor that prints "MyThread".