java网络编程对于循环结构的困惑

 package network06;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class Sever {
    public static void main(String[] args) {
        new Sever().startup();
    }
    private void startup(){
        ServerSocket ss =null;
        Socket s= null;
        try {
            ss =new ServerSocket(5858);
            while(true){
                s =ss.accept();//来一个就创建一个Socket对象
                SeverThread st = new SeverThread(s);//这两句无非是为了run()方法
                new Thread(st).start();             //
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally{
                try {
                    if(ss!=null)ss.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
        }
    }
    private class SeverThread implements Runnable{
        private Socket s= null;
        private BufferedReader br=null;
        private PrintWriter pw = null;
        private String name ;
        private boolean flag =true;

        public SeverThread(Socket s) throws IOException {
            this.s =s;
            br =new BufferedReader(new InputStreamReader(s.getInputStream()));
            pw = new PrintWriter(s.getOutputStream(),true);
            name = s.getInetAddress().getHostAddress()+":"+s.getPort();
            System.out.println(name+"已经连接上");
        }
        private void receive() throws IOException{
            String str=null;
            while((str=br.readLine())!=null){
                if(str.equalsIgnoreCase("quite")){
                    stop();
                    //关闭，进行资源的释放
                    pw.println("close");
                    break;
                }
                System.out.println(name+"--"+str);
                pw.println("Receive"+str);

            }
            System.out.println(name+"已经离开");
        }
        private void stop(){
            flag=false;
        }

        public void run() {
            try {
                //while(true){
                //  if(!flag)break;
                    receive();
                //}
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }finally{
                try {
                    if(s!=null)s.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }

    }

}

线程调用run()方法，这个外层循环结构，有什么作用？while((str=br.readLine())!=null)好像可以控制输入循环，就一直等着我们输入

https://www.cnblogs.com/dongguacai/p/5747397.html