Animacion Sencilla en Java usando un circulo

Codigo

package masterdavidjavabasico;

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

public class Demo1 extends JComponent {

    private final static int ANCHO = 512;

    private final static int ALTO = 384;

    private final static int DIAMETRO = 20;

    private float x, y;

    private float vx, vy;

    public Demo1() {
        setPreferredSize(new Dimension(ANCHO, ALTO));
        x = 10;
        y = 20;
        vx = 300;
        vy = 400;
    }

    private void fisica(float dt) {
        x += vx * dt;
        y += vy * dt;
        if (vx < 0 && x <= 0 || vx > 0 && x + DIAMETRO >= ANCHO)
            vx = -vx;
        if (vy < 0 && y < 0 || vy > 0 && y + DIAMETRO >= ALTO)
            vy = -vy;
    }

    public void paint(Graphics g) {
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, ANCHO, ALTO);
        g.setColor(Color.RED);
        g.fillOval(Math.round(x), Math.round(y), DIAMETRO, DIAMETRO);
    }

    private void dibuja() throws Exception {
        SwingUtilities.invokeAndWait(new Runnable() {
                public void run() {
                    paintImmediately(0, 0, ANCHO, ALTO);
                }
            });
    }

    public void cicloPrincipalJuego() throws Exception {
        long tiempoViejo = System.nanoTime();
        while (true) {
            long tiempoNuevo = System.nanoTime();
            float dt = (tiempoNuevo - tiempoViejo) / 1000000000f;
            tiempoViejo = tiempoNuevo;
            fisica(dt);
            dibuja();
        }
    }

    public static void main(String[] args) throws Exception {
        JFrame jf = new JFrame("Demo1");
        jf.addWindowListener(new WindowAdapter() {
                public void windowClosing(WindowEvent e) {
                    System.exit(0);
                }
            });
        jf.setResizable(false);
        Demo1 demo1 = new Demo1();
        jf.getContentPane().add(demo1);
        jf.pack();
        jf.setVisible(true);
        demo1.cicloPrincipalJuego();
    }
}

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Animacion Relog en Java Con Imagenes

Capturas 

Codigo

package relog03dic09;

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

/**
 *
 * @author Master
 */
public class AnimadorLogo extends JPanel
        implements ActionListener{
    protected ImageIcon imagenes[]; // declaramos un arreglo de imagenes
    protected int totalImagenes=24, //variable de tipo entero ultima imagen
            imagenActual=0, // variable de tipo entero primera imagen
            retardoAnimacion=1500; //1500 milisegundos de retardo
    protected Timer cronoAnimacion; // variable de tipo tiempo
    public AnimadorLogo() // constructor
    {
        setSize(getPreferredSize()); // toma el valor de las dimenciones de la imagen
        imagenes=new ImageIcon[totalImagenes]; // manda una instancia al arreglo de imagenes
        for(int i=0; i<imagenes.length; ++i) // se hace un incremento en i empesando de 0 de 1 en 1 hasta el valor asignado a la variable totalImagenes
            imagenes[i]=
                    new ImageIcon("imgrelog/relog"+i+".gif"); // genera un nombre para la imagen y lo va cambiando dependiendo el valor de i
        iniciaAnimacion(); // manda a llamar el metodo iniciaAnimacion que esta mas abajo
            }
public void paintComponent(Graphics g)
{
        super.paintComponent(g);//inicia los componentes del metodo graphics
if(imagenes[imagenActual].getImageLoadStatus()==MediaTracker.COMPLETE){//va cambiando la imagen
    imagenes[imagenActual].paintIcon(this, g, 0, 0);// imprime la imagen en las cordenandas 0,0
            imagenActual=(imagenActual+1)%totalImagenes;// cuando la imagen llega a la ultima regresa al principio
}


}
public void actionPerformed(ActionEvent e)
{
    repaint();// actualiza la ventana para que no se amontonen las imagenes
}
public void iniciaAnimacion()
{
    if(cronoAnimacion ==null){
        imagenActual=0;
        cronoAnimacion = new Timer(retardoAnimacion, this);
        cronoAnimacion.start();
    }
    else
        if(!cronoAnimacion.isRunning())
            cronoAnimacion.restart();
}
public void terminaAnimacion()
{
    cronoAnimacion.stop();
}
public Dimension getMinimumSize()
{
    return getPreferredSize();
}
public Dimension getPreferedSize()
{
    return new Dimension(500,500);
}
public static void main(String args[])
{
    AnimadorLogo anim = new AnimadorLogo();
    JFrame app = new JFrame("Master Animacion");
    app.getContentPane().add( anim, BorderLayout.CENTER);
    app.addWindowListener(new WindowAdapter(){
        public void windowClosing(WindowEvent e)
        {
            System.exit(0);
        }
    }
    );
    app.setSize ( anim.getPreferredSize().width+58+250,
            anim.getPreferredSize().height+80+250);
    app.show();
}
}

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Interfas en Java con Imagen de Fondo - Programa para el calculo de resistencias

Capturas

Codigo

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

/*
 * masterdavid.java
 *
 * Created on 15/12/2009, 12:06:35 AM
 */

package resistenciasmasterdavid;

/**
 *
 * @author Master David
 */
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.event.ComponentListener;
import java.awt.event.ComponentEvent;
import com.sun.awt.AWTUtilities;
import java.util.Locale;

public class masterdavid extends javax.swing.JFrame {
    int fr1,fr2,fr3,fr4;
    private javax.swing.JLabel jLabel6;
    private javax.swing.JLabel jLabel3;
    private javax.swing.JLabel jLabel4;
    private javax.swing.JLabel jLabel5;
    private javax.swing.JButton jButton1;
private javax.swing.JButton boton0;
private javax.swing.JButton boton1;
private javax.swing.JButton boton2;
private javax.swing.JButton boton3;
private javax.swing.JButton boton4;
private javax.swing.JButton boton5;
private javax.swing.JButton boton6;
private javax.swing.JComboBox jComboBox1;
private javax.swing.JComboBox jComboBox2;
private javax.swing.JComboBox jComboBox3;
private javax.swing.JComboBox jComboBox4;
private javax.swing.JTextField jTextField1;
private javax.swing.JTextField jTextField2;
private javax.swing.JTextField jTextField3;
private javax.swing.JTextField jTextField4;
    /** Creates new form masterdavid */
    public masterdavid() {
        jLabel6 = new javax.swing.JLabel();
        jLabel3 = new javax.swing.JLabel();
        jLabel4 = new javax.swing.JLabel();
        jLabel5 = new javax.swing.JLabel();
        jButton1 = new javax.swing.JButton();
         boton0 = new javax.swing.JButton();
         boton1 = new javax.swing.JButton();
         boton2 = new javax.swing.JButton();
         boton3 = new javax.swing.JButton();
         boton4 = new javax.swing.JButton();
         boton5 = new javax.swing.JButton();
         boton6 = new javax.swing.JButton();
         jComboBox1 = new javax.swing.JComboBox();
         jComboBox2 = new javax.swing.JComboBox();
         jComboBox3 = new javax.swing.JComboBox();
         jComboBox4 = new javax.swing.JComboBox();
         jTextField1 = new javax.swing.JTextField();
         jTextField2 = new javax.swing.JTextField();
         jTextField3 = new javax.swing.JTextField();
         jTextField4 = new javax.swing.JTextField();


//boton0
         boton0 = new JButton("");
                boton0.setBackground(Color.white);
                boton0.setBounds(new Rectangle(200+52,112,32,110));
                add(boton0);
                boton0.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                boton1ActionPerformed(evt);
            }
                 });
//boton1
                boton1 = new JButton("");
                boton1.setBackground(Color.white);
                boton1.setBounds(new Rectangle(300-2,112,32,110));
                add(boton1);

                boton2 = new JButton("");
                boton2.setBackground(Color.white);
                boton2.setBounds(new Rectangle(252+96,112,32,110));
                add(boton2);

                boton3 = new JButton("");
                boton3.setBackground(Color.white);
                boton3.setBounds(new Rectangle(252+147,112,32,110));
                add(boton3);
//Por colores
                boton4 = new JButton("Por Colores");
                boton4.setBounds(new Rectangle(50,50,120,20));
                add(boton4);
                boton4.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                boton4ActionPerformed(evt);
            }
                 });

//Por valor
                boton5 = new JButton("Por Valor");
                boton5.setBounds(new Rectangle(50,90,120,20));
               
                boton5.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                boton5ActionPerformed(evt);
            }
                 });

//Calcular
                boton6 = new JButton("Obtener Valor");
                boton6.setBounds(new Rectangle(100,300,120,20));
                add(boton6);
                boton6.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                boton6ActionPerformed(evt);
            }
                 });

//combobox1
                jComboBox1.setModel(new javax.swing.DefaultComboBoxModel(new String[] { "1","Negro", "Cafe", "Rojo", "Naranja","Amarillo","Verde","Azul","Violeta","Gris","Blanco" }));
                jComboBox1.setBounds(200,60 , 70, 19);
                add(jComboBox1);
         jComboBox1.addItemListener(new java.awt.event.ItemListener() {
            public void itemStateChanged(java.awt.event.ItemEvent evt) {
                jComboBox1ItemStateChanged(evt);
            }
        });
//combobox2
       jComboBox2.setModel(new javax.swing.DefaultComboBoxModel(new String[] {"2","Negro", "Cafe", "Rojo", "Naranja","Amarillo","Verde","Azul","Violeta","Gris","Blanco" }));
                jComboBox2.setBounds(200+80,60 , 70, 19);
                add(jComboBox2);
         jComboBox2.addItemListener(new java.awt.event.ItemListener() {
            public void itemStateChanged(java.awt.event.ItemEvent evt) {
                jComboBox2ItemStateChanged(evt);
            }
        });

        //combobox3
        jComboBox3.setModel(new javax.swing.DefaultComboBoxModel(new String[] {"3","Negro", "Cafe", "Rojo", "Naranja","Amarillo","Verde","Azul","Violeta","Gris","Blanco" }));
                jComboBox3.setBounds(200+160,60 , 70, 19);
                add(jComboBox3);
         jComboBox3.addItemListener(new java.awt.event.ItemListener() {
            public void itemStateChanged(java.awt.event.ItemEvent evt) {
                jComboBox3ItemStateChanged(evt);
            }
        });

        //combobox4
        jComboBox4.setModel(new javax.swing.DefaultComboBoxModel(new String[] { "4", "Plateado", "Dorado" }));
                jComboBox4.setBounds(200+240,60 , 70, 19);
                add(jComboBox4);
         jComboBox4.addItemListener(new java.awt.event.ItemListener() {
            public void itemStateChanged(java.awt.event.ItemEvent evt) {
                jComboBox4ItemStateChanged(evt);
            }
        });
        // boton para cerrar
        jButton1.setIcon(new javax.swing.ImageIcon(getClass().getResource("/resistenciasmasterdavid/cerrar.png"))); // NOI18N
        jButton1.setBounds(580, 40, 30  , 20);
        add(jButton1);
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });
//resultado
        jLabel6.setText("El Valor de la Resistencia es: ");
        jLabel6.setBounds(170, 250, 170, 20);
        add(jLabel6);
        jTextField1.setText("Valor");
        jTextField1.setBounds(350, 250, 120, 20);
        add(jTextField1);
        //res max
        jLabel3.setText(" Valor Maximo: ");
                jLabel3.setBounds(250, 250+30, 170, 20);
        add(jLabel3);
        jTextField2.setText(" Valor Max");
        jTextField2.setBounds(350, 280, 120, 20);
        add(jTextField2);
        //res min
        jLabel4.setText(" Valor Minimo: ");
                jLabel4.setBounds(250, 250+60, 170, 20);
        add(jLabel4);
        jTextField3.setText("Valor Min");
        jTextField3.setBounds(350, 310, 120, 20);
        add(jTextField3);
        //tolerancia
        jLabel5.setText("Tolerancia: ");
                jLabel5.setBounds(270, 250+90, 170, 20);
        add(jLabel5);
        jTextField4.setText("Tolerancia");
        jTextField4.setBounds(350, 340, 120, 20);
        add(jTextField4);



         setUndecorated(true);
         setResizable(false);
        AWTUtilities.setWindowOpaque(this, false);
// setLocation(400, 300);
 setSize(660,440);
 setLocationRelativeTo(null);

initComponents();


      
    }

public void paintComponent(Graphics g) {
}
    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                         
    private void initComponents() {

        jLabel2 = new javax.swing.JLabel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("Resistencias Master David");
        setAlwaysOnTop(true);
        setCursor(new java.awt.Cursor(java.awt.Cursor.CROSSHAIR_CURSOR));

        jLabel2.setIcon(new javax.swing.ImageIcon(getClass().getResource("/resistenciasmasterdavid/masterbackground.png"))); // NOI18N

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addComponent(jLabel2))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addComponent(jLabel2)
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>                       
    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
        if(0==0){      
            System.exit(0);
        }
}
    //evento boton 1
    public void boton1ActionPerformed(java.awt.event.ActionEvent evt){
   if(0==0) {
  
   }
}
     //evento boton 4 por color
    public void boton4ActionPerformed(java.awt.event.ActionEvent evt){
   if(0==0) {
       jComboBox1.setSelectedItem(null);
       jComboBox2.setSelectedItem(null);
       jComboBox3.setSelectedItem(null);
       jComboBox4.setSelectedItem(null);
       jComboBox1.setEnabled(true);
       jComboBox2.setEnabled(true);
       jComboBox3.setEnabled(true);
       jComboBox4.setEnabled(true);
       boton0.setBackground(Color.white);
       boton1.setBackground(Color.white);
       boton2.setBackground(Color.white);
    boton3.setBackground(Color.white);
    boton4.setEnabled(false);
    boton5.setEnabled(true);
   }
}
         //evento boton 5 por valor
    public void boton5ActionPerformed(java.awt.event.ActionEvent evt){

   if(0==0) {
              jComboBox1.setSelectedItem(null);
       jComboBox2.setSelectedItem(null);
       jComboBox3.setSelectedItem(null);
       jComboBox4.setSelectedItem(null);
       boton0.setBackground(Color.white);
       boton1.setBackground(Color.white);
       boton2.setBackground(Color.white);
    boton3.setBackground(Color.white);
       jComboBox1.setEnabled(false);
       jComboBox2.setEnabled(false);
       jComboBox3.setEnabled(false);
       jComboBox4.setEnabled(false);
       boton5.setEnabled(false);
       boton4.setEnabled(true);

   }
}

    // evento de jcombobox1
private void jComboBox1ItemStateChanged(java.awt.event.ItemEvent evt) {
 //   int fr1=0;
    int opcion = jComboBox1.getSelectedIndex();
       if(opcion== 0){
           boton0.setBackground(Color.white);
       }
    if(opcion== 1){
        boton0.setBackground(Color.black);
        fr1=00;
       }
    if(opcion== 2){
       boton0.setBackground(new Color(152, 102, 0));
       fr1=10;
       }
    if(opcion== 3){
       boton0.setBackground(Color.red);
       fr1=20;
       }
    if(opcion== 4){
       boton0.setBackground(Color.ORANGE);
       fr1=30;
       }
    if(opcion== 5){
       boton0.setBackground(Color.yellow);
       fr1=40;
       }
    if(opcion== 6){
       boton0.setBackground(Color.GREEN);
       fr1=50;
       }
    if(opcion== 7){
       boton0.setBackground(Color.BLUE);
       fr1=60;
       }
    if(opcion== 8){
      boton0.setBackground(new Color(153,0,153));
      fr1=70;
       }
    if(opcion== 9){
       boton0.setBackground(Color.GRAY);
       fr1=80;
       }
    if(opcion== 10){
       boton0.setBackground(Color.white);
       fr1=90;
       }

    }
private void jComboBox2ItemStateChanged(java.awt.event.ItemEvent evt) {
  //  int fr2=0;
     int opcion2 = jComboBox2.getSelectedIndex();
       if(opcion2== 0){
           boton1.setBackground(Color.white);

       }
    if(opcion2== 1){
        boton1.setBackground(Color.black);
        fr2=0;
       }
    if(opcion2== 2){
       boton1.setBackground(new Color(152, 102, 0));
       fr2=1;
       }
    if(opcion2== 3){
       boton1.setBackground(Color.red);
       fr2=2;
       }
    if(opcion2== 4){
       boton1.setBackground(Color.ORANGE);
       fr2=3;
       }
    if(opcion2== 5){
       boton1.setBackground(Color.yellow);
       fr2=4;
       }
    if(opcion2== 6){
       boton1.setBackground(Color.GREEN);
       fr2=5;
       }
    if(opcion2== 7){
       boton1.setBackground(Color.BLUE);
       fr2=6;
       }
    if(opcion2== 8){
      boton1.setBackground(new Color(153,0,153));
      fr2=7;
       }
    if(opcion2== 9){
       boton1.setBackground(Color.GRAY);
       fr2=8;
       }
    if(opcion2== 10){
       boton1.setBackground(Color.white);
       fr2=9;
       }       // TODO add your handling code here:
    }
private void jComboBox3ItemStateChanged(java.awt.event.ItemEvent evt) {
 //   int fr3=0;
    int opcion3 = jComboBox3.getSelectedIndex();
       if(opcion3== 0){
           boton2.setBackground(Color.white);

       }
    if(opcion3== 1){
        boton2.setBackground(Color.black);
        fr3=1;
       }
    if(opcion3== 2){
       boton2.setBackground(new Color(152, 102, 0));
       fr3=10;
       }
    if(opcion3== 3){
       boton2.setBackground(Color.red);
       fr3=100;
       }
    if(opcion3== 4){
       boton2.setBackground(Color.ORANGE);
       fr3=1000;
       }
    if(opcion3== 5){
       boton2.setBackground(Color.yellow);
       fr3=10000;
       }
    if(opcion3== 6){
       boton2.setBackground(Color.GREEN);
       fr3=100000;
       }
    if(opcion3== 7){
       boton2.setBackground(Color.BLUE);
       fr3=1000000;
       }
    if(opcion3== 8){
      boton2.setBackground(new Color(153,0,153));
      fr3=10000000;
       }
    if(opcion3== 9){
       boton2.setBackground(Color.GRAY);
       fr3=100000000;
       }
    if(opcion3== 10){
       boton2.setBackground(Color.white);
       fr3=1000000000;
       }    // TODO add your handling code here:
    }
private void jComboBox4ItemStateChanged(java.awt.event.ItemEvent evt) {
    //int fr4=0;
    int opcion4 = jComboBox4.getSelectedIndex();
   
    if(opcion4== 0){// TODO add your handling code here:
        boton3.setBackground(Color.white);
       
    }
    if(opcion4== 1){// TODO add your handling code here:
        boton3.setBackground(new Color(204,204,204));
        fr4=10;
    }
    if(opcion4== 2){
        boton3.setBackground(new Color(204,204,0));
        fr4=5;
    }
    }
        public void boton6ActionPerformed(java.awt.event.ActionEvent evt){

            int resultadores;
            int mx;
            String max;
            int mn;
            String min;
            int tol=fr4;
            String tole;
            String produc;
   if(0==0) {
resultadores=(fr1+fr2)*fr3;
produc=resultadores+" ohms";
jTextField1.setText(produc);

tole=tol+" %";
jTextField4.setText(tole);

mx=resultadores+((resultadores*fr4)/100);
max=mx+" ohms";
jTextField2.setText(max);

mn=resultadores-((resultadores*fr4)/100);
min=mn+" ohms";
jTextField3.setText(min);

   }
}
    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new masterdavid().setVisible(true);

            }
        });

    }

    // Variables declaration - do not modify                    
    private javax.swing.JLabel jLabel2;
    // End of variables declaration                  
    private Image imagen = null;

}

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Logos del Tecnologico de Estudios Superiores de Huixquilucan

Establecer los componentes para la apariencia

el cuadro de texto que aparece debajo de la etiqueta tiene la apariencia de una
etiqueta. Esto le indica la potencia de la gestión de apariencias en Swing.

package masterdavidjavabasico;

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

/*
<APPLET
    CODE=plafcomponente.class
    WIDTH=210
    HEIGHT=200 >
</APPLET>
*/

public class plafcomponente extends JApplet
{
    public void init()
    {
        Container contentPane = getContentPane();

        JNewLabel jnewlabel = new JNewLabel(
                "Esta es una etiqueta falsa.");

        contentPane.setLayout(new FlowLayout());
                                   
        contentPane.add(new JLabel("Esta es una etiqueta real."));
        contentPane.add(jnewlabel);
    }
}

class JNewLabel extends JTextField
{
    public JNewLabel(String s)
    {
        super(s);
    }
    public void updateUI()
    {
        super.updateUI();

        setHighlighter(null);
        setEditable(false);

        LookAndFeel.installBorder(this, "Label.border");

        LookAndFeel.installColorsAndFont(this, "Label.background",
            "Label.foreground", "Label.font");
    }
}

Cambio de apariencia

muestra la applet con la apariencia Metal, Motify  y la de Windows. Cambiar entre estas apariencias es tan
fácil como hacer clic sobre un botón de opción.

package masterdavidjavabasico;

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


/*
<APPLET
    CODE=plaf.class
    WIDTH=210
    HEIGHT=200 >
</APPLET>
*/

public class plaf extends JApplet
{

    JRadioButton b1 = new JRadioButton("Metal"),
    b2 = new JRadioButton("Motif"),
    b3 = new JRadioButton("Windows");

    public void init()
    {
        Container contentPane = getContentPane();
        contentPane.add(new jpanel(), BorderLayout.CENTER);
    }

    class jpanel extends JPanel implements ActionListener
    {
        public jpanel()
        {
            add(new JButton("JBoton"));
            add(new JTextField("JCuadro_de_texto"));
            add(new JCheckBox("JCasilla_de_activacion"));
            add(new JRadioButton("JBoton_de_opcion"));
            add(new JLabel("JEtiqueta"));
            add(new JList(new String[] {
                "JLista Elemento 1", "JLista Elemento 2","JLista Elemento 3"}));
            add(new JScrollBar(SwingConstants.HORIZONTAL));

            ButtonGroup group = new ButtonGroup();
            group.add(b1);
            group.add(b2);
            group.add(b3);

            b1.addActionListener(this);
            b2.addActionListener(this);
            b3.addActionListener(this);

            add(b1);
            add(b2);
            add(b3);
        }

        public void actionPerformed(ActionEvent e)
        {
            JRadioButton src = (JRadioButton)e.getSource();

            try {
                if((JRadioButton)e.getSource() == b1)
                    UIManager.setLookAndFeel(
                      "javax.swing.plaf.metal.MetalLookAndFeel");
                else if((JRadioButton)e.getSource() == b2)
                    UIManager.setLookAndFeel(
                        "com.sun.java.swing.plaf.motif.MotifLookAndFeel");
                else if((JRadioButton)e.getSource() == b3)
                    UIManager.setLookAndFeel(
                        "com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
            }
            catch(Exception ex) {}

            SwingUtilities.updateComponentTreeUI(getContentPane());
        }
    }
}

Holo desde java Swing JFrame

Ahora, además, hemos usado el método setBounds para fijar la posición y
tamaño de la ventana JFrame.
package masterdavidjavabasico;

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


public class app extends JFrame
{
    jpanel j;

    public app()
    {
        super("Aplicacion Swing");

        Container contentPane = getContentPane();
        j = new jpanel();
        contentPane.add(j);
    }

    public static void main(String args[])
    {
        final JFrame f = new app();

        f.setBounds(100, 100, 300, 300);
        f.setVisible(true);
        f.setBackground(Color.white);
        //f.setDefaultCloseOperation(DISPOSE_ON_CLOSE);

        //f.addWindowListener(new WindowAdapter() {
        //    public void windowClosed(WindowEvent e) {
        //        System.exit(0);
        //    }
        //});

    }
}

class jpanel extends JPanel
{
    jpanel()
    {
        setBackground(Color.white);
    }

    public void paintComponent (Graphics g)
    {
        super.paintComponent(g);
        g.drawString("Hola desde Swing!", 0, 60);
    }
}