JTextField: Change the foreground color and save the content

Question

I have a frame with some JTextFields for the user insert some values. When the window is opened, the text fields have written, in gray, what the user should write in that container, like "value in seconds"...

I want to change the color of those letters (I think it is the foreground) to dark when the user starts to write in the JTextFields, and save to a String what is written by the user.

Answer 1

For the colour change you have to implement a FocusListener which sets the foreground with setForeground(). If you want to have a String of the current content of the JTextField you can achieve this with a DocumentListener to the underlying Document.

See this code as an example (I use blue and red for the colour and store the Text value of tf in the String content):

JTextField tf = new JTextFiedl();
tf.addFocusListener(new FocusListener()
{
    @Override
    public void focusGained(FocusEvent fe)
    {
        tf.setForeground(INACTIVE_COLOUR);
    }

    @Override
    public void focusLost(FocusEvent fe)
    {
        tf.setForeground(ACTIVE_COLOUR);
    }
});

A full working example is here:

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

public class TF
{
    private final Color ACTIVE_COLOUR = Color.BLUE;
    private final Color INACTIVE_COLOUR = Color.RED;

    private String content; //text of the text field is stored here

    private JTextField tf;
    private JTextField lbl;

    public TF()
    {
        JFrame mainFrame = new JFrame("Window");

        tf = new JTextField("Hint");
        lbl = new JTextField("click here to change focus");

        tf.setForeground(ACTIVE_COLOUR);

        setListeners();

        mainFrame.add(tf, BorderLayout.NORTH);
        mainFrame.add(lbl, BorderLayout.SOUTH);
        mainFrame.pack();
        mainFrame.setVisible(true);
    }

    private void setListeners()
    {
        tf.addFocusListener(new FocusListener()
        {
            @Override
            public void focusGained(FocusEvent fe)
            {
                tf.setForeground(INACTIVE_COLOUR);
            }

            @Override
            public void focusLost(FocusEvent fe)
            {
                tf.setForeground(ACTIVE_COLOUR);
            }
        });

        tf.getDocument().addDocumentListener(new DocumentListener()
        {
            @Override
            public void removeUpdate(DocumentEvent de)
            {
                content = tf.getText();
            }

            @Override
            public void insertUpdate(DocumentEvent de)
            {
                content = tf.getText();
            }

            @Override
            public void changedUpdate(DocumentEvent de)
            {
                content = tf.getText();
            }
        });
    }

    public static void main(String[] args)
    {
        TF tf = new TF();
    }
}