Applet Problem...

[Jeremy Parsons]

I am trying an applet I have been adding to through my study book, and it runs, but not right.. It's supposed to take the name I put in and display it back on the applet screen, but after I click the button I get nothing.. Here's the code:

 
import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
public class App extends Applet implements ActionListener
 
{
Label greeting = new Label("Hello. Who are you?");
Font bigFont = new Font("TimesRoman", Font.BOLD,36);
Button pressMe = new Button("Press Me");
TextField answer = new TextField("",10);
public void init()
 

 

{
greeting.setFont(bigFont);
add(greeting);
add(answer);
add(pressMe);
pressMe.addActionListener(this);
answer.addActionListener(this);
answer.requestFocus();
 
}
 
public void actionPerformed(ActionEvent thisEvent)
{
String name = answer.getText();
Label personalGreeting = new Label("");
personalGreeting.setText("Hi " + name);
add(personalGreeting);
}
 

 
}
 

Did I miss something, or is my pc just too slow to return the new output?

[Michael Dunn]

when adding/removing components in this manner you need to call validate()
(or revalidate() for swing components), and sometimes repaint() - safer to add it for all

    
    public void actionPerformed(ActionEvent thisEvent)
      {
        String name = answer.getText();
        Label personalGreeting = new Label("");
        personalGreeting.setText("Hi " + name);
        add(personalGreeting);
        validate();//<-----------
        repaint();//<-----------
      }
 

[Ulf Dittmer]

After adding components later in the applet lifecycle (like you are doing in the in the action handler), the applet layout needs to be refreshed. This is done with a call to "invalidate();".

[Jeremy Parsons]

I haven't learned the repaint method yet, but just did the invalidate and validate methods.. Thanks, I got it working now, plus I just read about the remove method.. Here's the working code..

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
public class App extends Applet implements ActionListener
 
{
Label greeting = new Label("Hello. Who are you?");
Font bigFont = new Font("TimesRoman", Font.BOLD,36);
Button pressMe = new Button("Press Me");
TextField answer = new TextField("",10);
public void init()
 

 

{
greeting.setFont(bigFont);
add(greeting);
add(answer);
add(pressMe);
pressMe.addActionListener(this);
answer.addActionListener(this);
answer.requestFocus();
 
}
 
public void actionPerformed(ActionEvent thisEvent)
{
String name = answer.getText();
Label personalGreeting = new Label("");
personalGreeting.setText("Hi " + name);
add(personalGreeting);
remove(answer);
remove(pressMe);
invalidate();
validate();
}
 

 
}

[Jeremy Parsons]

as a side thought, why do I need two method bodies instead of one like most of the programs I have made using Java? Is it just with Applets or what??

[Ilja Preuss]

Originally posted by Jeremy Parsons:
as a side thought, why do I need two method bodies instead of one like most of the programs I have made using Java? Is it just with Applets or what??

I don't understand the question. What two method bodies?

[Jeremy Parsons]

public void init()
{ //body #1 statements;}

public void actionPerformed()
{ //body#2 statements;}

Or blocks of code if that's what you call them.. I learned they are method bodies in the study units I am working with...

[Ulf Dittmer]

It's good software practice to carve up your program into classes and methods, with each having a clearly defined task. You'll get to that later in your studies. Code that does initialization has really nothing to do with code for handling an event. Besides, the init code is called once, while the event handler is called multiple times. You wouldn't want the init stuff to happen over and over again.