GhostText.java

package me.corriekay.pokegoutil.utils.ui;

import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.JTextComponent;
import java.awt.*;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;

public class GhostText implements FocusListener, DocumentListener, PropertyChangeListener {
    private final JTextComponent textComp;
    private boolean isEmpty;
    private Color ghostColor;
    private Color foregroundColor;
    private final String ghostText;

    public GhostText(final JTextComponent textComp, String ghostText) {
        super();
        this.textComp = textComp;
        this.ghostText = ghostText;
        this.ghostColor = Color.LIGHT_GRAY;
        textComp.addFocusListener(this);
        registerListeners();
        updateState();
        if (!this.textComp.hasFocus()) {
            focusLost(null);
        }
    }

    public void delete() {
        unregisterListeners();
        textComp.removeFocusListener(this);
    }

    private void registerListeners() {
        textComp.getDocument().addDocumentListener(this);
        textComp.addPropertyChangeListener("foreground", this);
    }

    private void unregisterListeners() {
        textComp.getDocument().removeDocumentListener(this);
        textComp.removePropertyChangeListener("foreground", this);
    }

    public Color getGhostColor() {
        return ghostColor;
    }

    public void setGhostColor(Color ghostColor) {
        this.ghostColor = ghostColor;
    }

    private void updateState() {
        isEmpty = textComp.getText().length() == 0;
        foregroundColor = textComp.getForeground();
    }

    @Override
    public void focusGained(FocusEvent e) {
        if (isEmpty) {
            unregisterListeners();
            try {
                textComp.setText("");
                textComp.setForeground(foregroundColor);
            } finally {
                registerListeners();
            }
        }

    }

    @Override
    public void focusLost(FocusEvent e) {
        if (isEmpty) {
            unregisterListeners();
            try {
                textComp.setText(ghostText);
                textComp.setForeground(ghostColor);
            } finally {
                registerListeners();
            }
        }
    }

    @Override
    public void propertyChange(PropertyChangeEvent evt) {
        updateState();
    }

    @Override
    public void changedUpdate(DocumentEvent e) {
        updateState();
    }

    @Override
    public void insertUpdate(DocumentEvent e) {
        updateState();
    }

    @Override
    public void removeUpdate(DocumentEvent e) {
        updateState();
    }

}