为什么ThreadLocal变量需要静态？(Why ThreadLocal variable need to static?)

 我已经阅读了很多关于为什么ThreadLocal变量需要静态（尽管不是必需）的文章，但我没有明白为什么它应该是静态的。 
 
 我在这里阅读了许多其他链接，但没有得到这个想法。 
 
 我做过类似的事 
 
public class ThreadLocalDemo{

    public static void main(String[]args)throws Exception{
        SharedRersource r1= new SharedRersource();
        Thread t1= new Thread(r1);
        Thread t2= new Thread(r1);
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println("Main thread Exiting...");
        }

    }

class SharedRersource implements Runnable{


        private ThreadLocal<Integer> threadId = new ThreadLocal(){
            protected Integer initialValue(){
                return (int)(Math.random()*100);
                }
        };
        public void run(){

            try{
                Thread.sleep(2000);
            }
            catch(InterruptedException e){
                e.printStackTrace();
                }
                System.out.println(threadId.get());

            }
        };
 
 这里线程t1和t2具有threadId的私有副本，而不是为什么它应该是静态的 
 
 请给我更好的理解。 谢谢 

I have read many articles on why ThreadLocal variable need to be static(although not necessary), but I didn't get the idea why it should be static.
 
I have read it here and many other links but didn't get the idea.
 
I have done something like this
 
public class ThreadLocalDemo{

    public static void main(String[]args)throws Exception{
        SharedRersource r1= new SharedRersource();
        Thread t1= new Thread(r1);
        Thread t2= new Thread(r1);
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println("Main thread Exiting...");
        }

    }

class SharedRersource implements Runnable{


        private ThreadLocal<Integer> threadId = new ThreadLocal(){
            protected Integer initialValue(){
                return (int)(Math.random()*100);
                }
        };
        public void run(){

            try{
                Thread.sleep(2000);
            }
            catch(InterruptedException e){
                e.printStackTrace();
                }
                System.out.println(threadId.get());

            }
        };
 
Here thread t1 and t2 is having private copy of threadId than why It should be static
 
Please give a better understanding to me. Thanks 

原文：https://stackoverflow.com/questions/35764959