Action Listener error

Question

I keep getting an error when I implement the ActionListener. I dont really understand how to fix it. I did the actionPerformed (ActionEvent ev) {} and put my login button to call it with lg.addActionListener(this);

import java.awt.*;
import javax.swing.*;
import java.awt.Event.*;
import java.applet.Applet;

public class LoginScreen extends JApplet implements ActionListener   {
    JTextField un;
    JPasswordField pw;
    JButton lg;
    JLabel user,pass;

    public LoginScreen () {
        un = new JTextField ();
        pw = new JPasswordField ();
        lg = new JButton ("login");
        user = new JLabel ("username");
        pass = new JLabel ("password");

        lg.addActionListener(this);

        this.setLayout(null);

        user.setBounds(10, 10, 120, 20);
        pass.setBounds(10, 30, 120, 20);
        un.setBounds(140, 10, 200, 20);
        pw.setBounds(140, 30, 200, 20);

        lg.setBounds(140, 55, 100, 20);

        this.add(user);
        this.add(pass);
        this.add(un);
        this.add(pw);
        this.add(lg);

        this.setSize(500, 300);
        this.setVisible(true);
        }       
    public void actionPerformed(ActionEvent ev) {

    }
}

First bad practice `setLayout(null)` 2nd) implements ActionListener in a top level class, 3rd) Not add @Override annotation in `actionPerformed()` 4th) Your method implementation is empty.. — nachokk, Jan 02 '14 at 03:05
1) Java GUIs might have to work on a number of platforms, on different screen resolutions & using different PLAFs. As such they are not conducive to exact placement of components. To organize the components for a robust GUI, instead use layout managers, or [combinations of them](http://stackoverflow.com/a/5630271/418556), along with layout padding & borders for [white space](http://stackoverflow.com/q/17874717/418556). 2) `this.setSize(500, 300);` An applet's size is set in HTML. It should not be set in code. .. — Andrew Thompson, Jan 02 '14 at 06:24
.. 3) Why code an applet? If it is due to spec. by teacher, please refer them to [Why CS teachers should stop teaching Java applets](http://programmers.blogoverflow.com/2013/05/why-cs-teachers-should-stop-teaching-java-applets/). 4) Always copy/paste error & exception output. — Andrew Thompson, Jan 02 '14 at 06:28

score 5 · Answer 1 · answered Jan 02 '14 at 03:06

5

Change import java.awt.Event.*; to import java.awt.event.*;

Java is case-sensitive.

Also change import java.applet.Applet; -> import javax.swing.JApplet;

answered Jan 02 '14 at 03:06

Sibbo

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Paul Samsotha · Answer 2 · 2014-01-02T03:30:07.597

4

You have the wrong imports. You need. import java.awt.event.*; or

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

The latter is better practice

If you're using one of the following IDEs (with default configuration), this is easily fixed with a couple buttons.

Eclipse Ctrl + Shift + O

Netbeans Ctrl + Shift + I

edited Jan 02 '14 at 03:30

answered Jan 02 '14 at 03:06

Paul Samsotha

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@Josh Enselma It wasn't that fast. I just copied and pasted the code and I spotted the error fairly quick. I actually a pretty slow typer compared to others. I'm still have to look at the keyboard a lot of times :) – Paul Samsotha Jan 02 '14 at 03:12
@peeskillet you have to look? i don't believe you – nachokk Jan 02 '14 at 03:14
Since he has `import java.awt.*;` , he can just remove the faulty ones? – WonderWorld Jan 02 '14 at 03:15
1

@Xbit, `java.awt.*` doesn't import `java.awt.event.*` – Paul Samsotha Jan 02 '14 at 03:16
@peeskillet i see, it uses more then only java.awt. – WonderWorld Jan 02 '14 at 03:28

score 2 · Answer 3 · answered Jan 02 '14 at 03:07

2

import java.awt.Event.*;

needs to be

import java.awt.event.*;

This causes a compile error. Once this has been fixed, you need to write some code in the actionPerformed or nothing will happen when you button is pressed.

answered Jan 02 '14 at 03:07

Josh Engelsma

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+! I think the OP knows the second part. Besides there isn't even a `main` to run the program, so I think the question was just an example duplicating the error :) – Paul Samsotha Jan 02 '14 at 03:34
1

Thanks, I also upvoted yours! I admit you beat me to the answer first, second time that has happened to me today..so frustrating haha. I agree that he most likely knows about the second part, however, you never know based on some of the questions I have seen on SO :) – Josh Engelsma Jan 02 '14 at 03:40
thanks this helped me a lot. case sensitivity always gets me. – mike-gallego Jan 02 '14 at 03:44
Not a problem, consider accepting an answer so that this question is resolved on stackoverflow – Josh Engelsma Jan 02 '14 at 03:49

score 0 · Answer 4 · answered Jan 02 '14 at 03:05

0

In your actionPerformed method, if you do not specify any action, your button will do nothing.

answered Jan 02 '14 at 03:05

Anonymous Noob

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Action Listener error

4 Answers4