JLabel gradient background.

Realizar JLabel con color de fondo gradiente.

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Algo que se ve muy bien en las aplicaciones de escritorio en Java, son los titulos con un color de fondo gradiente (JLabel Gradient Background), para hacerlo solo hay que sobreescribir el metodo void paintComponent(Graphics g) de la clase JComponent, recuerda que esta es la clase base para los componentes SWING.
Para lograr un color de fondo gradiente horizontal:

JLabel Gradiente

Hay que implementar este codigo:

  JLabel label = new JLabel("...... DatoJava ......") {
   @Override
   protected void paintComponent(Graphics g) {
    Color colorFinal = new Color(255, 1, 1);
    
    Graphics2D graphics2d = (Graphics2D) g.create();
    graphics2d.setPaint(new GradientPaint(0, 0, getBackground(),
      getWidth(), 0, colorFinal));
    graphics2d.fillRect(0, 0, getWidth(), getHeight());
    graphics2d.dispose();
    
    super.paintComponent(g);
   }
  };
    

Para lograr un color de fondo gradiente vertical:

JLabel Gradiente

Hay que implementar este codigo:

  JLabel label = new JLabel("...... DatoJava ......") {
   @Override
   public void setForeground(Color fg) {
    super.setForeground(fg.RED);
   }

   @Override
   protected void paintComponent(Graphics g) {
    LinearGradientPaint linearGradientPaint = new LinearGradientPaint(
      new Point(0, 10), new Point(0, getHeight()),
      new float[] { 0.240f, 0.250f }, new Color[] {
        Color.LIGHT_GRAY, Color.GRAY });

    Graphics2D graphics2d = (Graphics2D) g.create();
    graphics2d.setPaint(linearGradientPaint);
    graphics2d.fill(new Rectangle(0, 0, getWidth(), getHeight()));
    graphics2d.dispose();

    super.paintComponent(g);
   }
  };
    

Con esto podemos jugar y hacer varias cosas interesantes, por ejemplo:

JLabel Esquina Gradiente

  JLabel label = new JLabel("...... DatoJava ......") {
   @Override
   protected void paintComponent(Graphics g) {
    LinearGradientPaint linearGradientPaint = new LinearGradientPaint(
      new Point(0, 10), new Point(10, getHeight()),
      new float[] { 0.240f, 0.250f }, new Color[] {
        Color.BLACK, getBackground() });

    Graphics2D graphics2d = (Graphics2D) g.create();
    graphics2d.setPaint(linearGradientPaint);
    graphics2d.fill(new Rectangle(0, 0, getWidth(), getHeight()));
    graphics2d.dispose();

    super.paintComponent(g);
   }
  };
    

JLabel Linea Abajo

  JLabel label = new JLabel("...... DatoJava ......") {
   @Override
   protected void paintComponent(Graphics g) {
    LinearGradientPaint linearGradientPaint = new LinearGradientPaint(
      new Point(0, 25), new Point(0, getHeight()),
      new float[] { 0.240f, 0.250f }, new Color[] {
        getBackground(), Color.RED });

    Graphics2D graphics2d = (Graphics2D) g.create();
    graphics2d.setPaint(linearGradientPaint);
    graphics2d.fill(new Rectangle(0, 0, getWidth(), getHeight()));
    graphics2d.dispose();

    super.paintComponent(g);
   }
  };
    

JLabel Linea Abajo

  JLabel label = new JLabel("...... DatoJava ......") {
   @Override
   protected void paintComponent(Graphics g) {
    Color colorFinal = new Color(0, 0, 0);
    Graphics2D graphics2d = (Graphics2D) g.create();
    graphics2d.setPaint(new GradientPaint(0, 0, getBackground(),
      getWidth(), 0, colorFinal));
    graphics2d.fillRect(0, 25, getWidth(), getHeight());
    graphics2d.dispose();

    super.paintComponent(g);
   }
  };
    

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