variable access from a constructor

i got command line argument for a user name. I then initialized it in constructor of the class.

i created a thread from this constructor and tried using this name variable in run method.

It returns null . How do i use this variable inside a run method.

i tried using getName method which return name. But it returns null too.

Hi,

It would be useful if you posted the whole code.

You are saying that you initialize the name variable in the constructor of the AppServer class and start a thread from it.
However, in the code you posted you start a thread from the constructor of the AppClient class....

Cheers,
Michael

Michael Krimgen wrote:Hi,

It would be useful if you posted the whole code.

You are saying that you initialize the name variable in the constructor of the AppServer class and start a thread from it.
However, in the code you posted you start a thread from the constructor of the AppClient class....

Cheers,
Michael

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;

public class AppServer extends Frame implements ActionListener,Runnable
{
 //Declarations
 Button b1;
 TextField tf;
 TextArea ta;
 ServerSocket ss;
 Socket s;
 PrintWriter pw;
 BufferedReader br;
 Thread th;
 String name;
 
 public AppServer(int port,String name)
 {
  Frame f=new Frame("Server Side Chatting");//Frame for Server
  f.setLayout(new FlowLayout());//set layout
  
  b1=new Button("Send");//Send Button
  
  b1.addActionListener(this);//Add action listener to send button.
  tf=new TextField(15);
  ta=new TextArea(12,20);
  port=port;
  //name=name;
  //System.out.println(name);
  f.addWindowListener(new W1());//add Window Listener to the Frame
  f.add(tf);//Add TextField to the frame
  f.add(b1);//Add send Button to the frame
  f.add(ta);//Add TextArea to the frame
  try{
   ss=new ServerSocket(port);//Socket for server
   s=ss.accept();//accepts request from client
   System.out.println(s);
   //below line reads input from InputStreamReader
   br=new BufferedReader(new InputStreamReader(s.getInputStream()));
   //below line writes output to OutPutStream
   pw=new PrintWriter(s.getOutputStream(),true);
  }catch(Exception e)
  {
  }
  th=new Thread(this);//start a new thread
  //th.setDaemon(true);//set the thread as demon
  th.start();
  //setFont(new Font("Arial",Font.BOLD,20));
  f.setSize(200,200);//set the size
  f.setLocation(300,300);//set the location
  f.setVisible(true);
  //f.validate();
 }
 //method required to close the Frame on clicking "X" icon.
 private class W1 extends WindowAdapter
 {
  public void windowClosing(WindowEvent we) 
  {
   System.exit(0);
  }
 }
 public String getName()
 {
  return name;
 }
 //This method will called after clicking on Send button.
 public void actionPerformed(ActionEvent ae)
 {
  ta.append("myself:"+tf.getText()+"\n");
  pw.println(tf.getText());//write the value of textfield into PrintWriter
  tf.setText("");//clean the textfield
 }
 //Thread running as a process in background
 public void run()
 {
  while(true)
  {
   try{
    String s=br.readLine();//reads the input from textfield
    ta.append(name +": "+s+"\n");//Append to TextArea
   }catch(Exception e)
   {
   }
  } 
 }
 //Main method
 public static void main(String args[]) 
 {
  //Instantiate AppServer class
  int port=Integer.parseInt(args[0]);
  String name=args[1];
  AppServer server = new AppServer(port,name);//name
 }
}

akila sekaran wrote:

Michael Krimgen wrote:Hi,

It would be useful if you posted the whole code.

You are saying that you initialize the name variable in the constructor of the AppServer class and start a thread from it.
However, in the code you posted you start a thread from the constructor of the AppClient class....

Cheers,
Michael

import java.awt.*; import java.awt.event.*; import java.io.*; import java.net.*; public class AppServer extends Frame implements ActionListener,Runnable { //Declarations Button b1; TextField tf; TextArea ta; ServerSocket ss; Socket s; PrintWriter pw; BufferedReader br; Thread th; String name; public AppServer(int port,String name) { Frame f=new Frame("Server Side Chatting");//Frame for Server f.setLayout(new FlowLayout());//set layout b1=new Button("Send");//Send Button b1.addActionListener(this);//Add action listener to send button. tf=new TextField(15); ta=new TextArea(12,20); port=port; //name=name; //System.out.println(name); f.addWindowListener(new W1());//add Window Listener to the Frame f.add(tf);//Add TextField to the frame f.add(b1);//Add send Button to the frame f.add(ta);//Add TextArea to the frame try{ ss=new ServerSocket(port);//Socket for server s=ss.accept();//accepts request from client System.out.println(s); //below line reads input from InputStreamReader br=new BufferedReader(new InputStreamReader(s.getInputStream())); //below line writes output to OutPutStream pw=new PrintWriter(s.getOutputStream(),true); }catch(Exception e) { } th=new Thread(this);//start a new thread //th.setDaemon(true);//set the thread as demon th.start(); //setFont(new Font("Arial",Font.BOLD,20)); f.setSize(200,200);//set the size f.setLocation(300,300);//set the location f.setVisible(true); //f.validate(); } //method required to close the Frame on clicking "X" icon. private class W1 extends WindowAdapter { public void windowClosing(WindowEvent we) { System.exit(0); } } public String getName() { return name; } //This method will called after clicking on Send button. public void actionPerformed(ActionEvent ae) { ta.append("myself:"+tf.getText()+"\n"); pw.println(tf.getText());//write the value of textfield into PrintWriter tf.setText("");//clean the textfield } //Thread running as a process in background public void run() { while(true) { try{ String s=br.readLine();//reads the input from textfield ta.append(name +": "+s+"\n");//Append to TextArea }catch(Exception e) { } } } //Main method public static void main(String args[]) { //Instantiate AppServer class int port=Integer.parseInt(args[0]); String name=args[1]; AppServer server = new AppServer(port,name);//name } }

this is the code . Sorry that was a typo in the class name of my previous code sample

First - you comment the line which is supposed to do the assignment.

Second - your parameter has the same name as the instance variable, and so the local parameter would hide the instance variable: so doing name = name is a non-action (assigning a value to itself). You want to qualify which name variable you want to assign to using the this keyword: this.name = name.

Steve Luke wrote:First - you comment the line which is supposed to do the assignment.

Second - your parameter has the same name as the instance variable, and so the local parameter would hide the instance variable: so doing name = name is a non-action (assigning a value to itself). You want to qualify which name variable you want to assign to using the this keyword: this.name = name.

ohh yeahhh thanks a lot. "this" worked!! My code works fine now

There are tricks to make this less likely to happen in the future. One such trick is to always make your method parameters final: public AppServer(final int port, final String name). Then if you tried name = name you would get a compile-time error that points to the offending line rather than a run-time behavior problem which occurs in a different method at some later point.

Behaviorally, another thing I like to do is get in the habit of always using the this keyword to qualify instance variable references.

Steve Luke wrote:There are tricks to make this less likely to happen in the future. One such trick is to always make your method parameters final: public AppServer(final int port, final String name). Then if you tried name = name you would get a compile-time error that points to the offending line rather than a run-time behavior problem which occurs in a different method at some later point.

Behaviorally, another thing I like to do is get in the habit of always using the this keyword to qualify instance variable references.[/quote

Oh okay got it! thank you steve!