Why doesn't this ActionListener work?

Question

I am just learning to use ActionListener s and making widgets working. Here is my simple program that I want to print whatever i type in a JTextField .

TextViewer1

import javax.swing.JFrame;

public class TextViewer1 {

    /**
     * @param args
     */
    public static void main(String[] args) {
        JFrame frame = new TextFrame1();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);

    }

}

TextFrame1

import java.awt.event.ActionListener;
import javax.swing.*;

public class TextFrame1 extends JFrame {
    private static final int FRAME_WIDTH = 300;
    private static final int FRAME_HEIGHT = 200;

    public TextFrame1() {
        createComponents();
        setSize(FRAME_WIDTH, FRAME_HEIGHT);
    }


    private void createComponents() {
        JPanel panel = new JPanel();
        add(panel);

        JTextField textbox = new JTextField(20);
        panel.add(textbox);

        String TYPED = textbox.getText();
        ActionListener sendsText = new TextListener();
        textbox.addActionListener(sendsText);


    }
}

TextListener

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

public class TextListener implements ActionListener {

    /**
     * @param args
     */

    public void actionPerformed(ActionEvent event) {

        System.out.println(TYPED);

    }

}

So the problem is the variable TYPED in 'TextListener', it wants to create this variable and initialise it.

What is wrong?

Answer 1

So the problem is the variable TYPED in 'Text Listener', it wants to create this variable and initialise it.

This is because the variable is undefined in your TextListener . You create a local variable called TYPED in TextFrame1#createComponents but this is not visible in actionPerformed in TextListener .

In fact you are assigning the variable to the initial text of the of the JTextField which by default is an empty String . If you want to get the current text of the component, you could pass it into the constructor:

class TextListener implements ActionListener {

   private final JTextField textField;
   public TextListener(JTextField textField) {
    this.textField = textField;
   }

   @Override
   public void actionPerformed(ActionEvent event) {

      System.out.println(textField.getText());
   }
}

Create the TextListener like this:

ActionListener sendsText = new TextListener(textbox);

Answer 2

TYPED is not declared as a variable. So either declare it or surround it with "".

edit: Yes, you did declare it, but as a local variable within the createComponents functions inside the TextFrame1 class.

You need to pass the value like:

public class TextListener implements ActionListener {
    private String typed;

    public TextListener(String typed) {
        this.typed = typed;
    }

    /**
     * @param args
     */

    public void actionPerformed(ActionEvent event) {

        System.out.println(typed);

    }

}

Oh, and variables should not be in upper case but in lower case. Upper case is for constants.

edit 2:my bad, that listener constructor should have accepted String typed, not int typed. I fixed the code. As to your other issue, that is because you now need to pass the input result to the listener declaration.

 ActionListener sendsText = new TextListener(TYPED);

Or just do:

 ActionListener sendsText = new TextListener(textbox.getText());