求大神帮忙！！！关于java问题

Question

ChatHandler.java
package pro4;
import java.net.*;
import java.io.*;
import java.util.*;
public class ChatHandler implements Runnable{
    protected Socket socket;
    protected ObjectInputStream dataIn;
    protected ObjectOutputStream dataOut;
    protected Thread listener;
    protected static Vector handlers=new Vector();
     
    private boolean keepListening=true;
    public ChatHandler(Socket socket){
        this.socket=socket;
    }
    public synchronized void start(){
        if(listener==null){
            try{
                dataIn=new ObjectInputStream(socket.getInputStream());
                dataOut=new ObjectOutputStream(socket.getOutputStream());
                listener=new Thread(this);
                listener.start();
            }catch(IOException ioException){
                ioException.printStackTrace();
            }
        }
    }
    public synchronized void stop(){
        if(listener!=null){
            try{
                if(listener!=Thread.currentThread())
                    listener.interrupt();
                listener=null;
                dataOut.close();
                socket.close();
            }catch(IOException ignored){
                 
            }
        }
    }
    public void run(){
        String message="";
        try{
            handlers.addElement(this);
            while(keepListening){
                message=(String)dataIn.readObject();
                if(message.equals("DISCONNECT")){
                    dataOut.writeObject(message);
                    dataOut.flush();
                    stopListening();
                }else
                    broadcast(message);
            }
        }catch(ClassNotFoundException classNotFoundException){
             
        }catch(EOFException ignored){
             
        }catch(IOException ex){
            if(listener==Thread.currentThread())
                ex.printStackTrace();
        }finally{
            handlers.removeElement(this);
        }
        try{
            dataIn.close();
        }catch(IOException ioException){
            ioException.printStackTrace();
        }
        stop();
    }
    protected void broadcast(String message){
        synchronized (handlers){
            Enumeration enumer=handlers.elements();
            while(enumer.hasMoreElements()){
                ChatHandler handler=(ChatHandler)enumer.nextElement();
                try{
                    handler.dataOut.writeObject(message);
                    handler.dataOut.flush();
                }catch(IOException ex){
                    handler.stop();
                }              
            }
        }
    }
    public void stopListening(){
        keepListening=false;
    }
}

可以解释一下run（）方法和broadcast（）方法吗？看不懂，，，