接口是什么意思

Question

1. an interface represents a kind of behavior and consists of a set of method declarations2. Java documentation:
public String toString()
Returns a string representation of this thread, including the thread's name, priority, and thread group.

Answer 1

2. Thread.toString() => Thread[name,priority,thread group]

Answer 2

main 是他的thread group吗？
是否
 Thread.currentThread();
        
的一定是main

Answer 3

不见得，那个是main因为它是那个默认的ThreadGroup，你可以把线程加到别的group里去，譬如class twothread implements Runnable
{
    twothread()
    {
        Thread t1=Thread.currentThread();
        t1.setName("The first main thread");
        System.out.println("The running thread:"+t1); //*********************************
ThreadGroup tg = new ThreadGroup("another thread group");
        Thread t2=new Thread(tg, this,"these cond thread");
        System.out.println("creat another thread");
        t2.start();
        try
        {
            System.out.println("first thread will sleep");
            Thread.sleep(3000);
        }
        catch(InterruptedException e)
        {
            System.out.println("first thread has wrong");
        }
        System.out.println("first thread exit");
    }
    public void run()
    {
        try
        {
            for(int i=0;i<5;i++)
            {
                System.out.println("Sleep time for thread2:"+i);
System.out.println("The running thread:"+Thread.currentThread()); 
                Thread.sleep(1000);
            }
        }
        catch(InterruptedException e)
        {
            System.out.println("thread has wrong");
        }
        System.out.println("second thread exit");
    }
    public static void main(String args[])
    {
        new twothread();
    }
}output:
The running thread:Thread[The first main thread,5,main]
creat another thread
first thread will sleep
Sleep time for thread2:0
The running thread:Thread[these cond thread,5,another thread group]
Sleep time for thread2:1
The running thread:Thread[these cond thread,5,another thread group]
Sleep time for thread2:2
The running thread:Thread[these cond thread,5,another thread group]
first thread exit
Sleep time for thread2:3
The running thread:Thread[these cond thread,5,another thread group]
Sleep time for thread2:4
The running thread:Thread[these cond thread,5,another thread group]
second thread exit

Answer 4

public interface Transformer
public Object transform(Object input)
Transforms the input object (leaving it unchanged) into some output object.
Returns:
the transformation of the input object to the output object

Answer 5

又是 English？
又恨又爱……

Answer 6

new Thread(tg, this,"these cond thread");this 在这里表示什么意思。

Answer 7

this = the current object, in this case, a twothread instance

Answer 8

this = the current object, in this case, a twothread instance

Answer 9

Thread(ThreadGroup group, Runnable target, String name)this 应该是 target 吧？
target 是代表什么？