import java.awt.*;
import java.awt.event.*;

public class CambiaColore2 extends    Frame
                           implements ActionListener
{ 
   private Color[] cCOLORI={ 
      Color.black    , Color.blue   , Color.cyan  ,
      Color.darkGray , Color.gray   , Color.green ,
      Color.lightGray, Color.magenta, Color.orange,
      Color.pink     , Color.red    , Color.white ,
      Color.yellow }; 
   private String[] sCOLORI={
      "Nero"         , "Blu"        , "Azzurro"   ,
      "Grigio scuro" , "Grigio"     , "Verde"     ,
      "Grigio chiaro", "Magenta"    , "Arancione" ,
      "Rosa", "Rosso", "Bianco"     ,
      "Giallo" };

   private Panel  paNORD, paSUD;
   private Choice colori;
   private Button cambia, cambia2; 
   private Color  sfondo;
   private Canvas tela; 

   private Label tAlphaf, tAlpha, tAlphaH,
                 tBluef,  tBlue,  tBlueH,
                 tGreenf, tGreen, tGreenH,
                 tRedf,   tRed,   tRedH,
                 tRGB,    tRGBH,
                 tsRGB,   tsRGBH; 

   public CambiaColore2()
   { 
      colori=new Choice();                 for(int i=0; i < sCOLORI.length; i++)
                                              colori.add(sCOLORI[i]);
      tela=new Canvas();                   sfondo=cCOLORI[0];
                                           tela.setBackground(sfondo);
      cambia =new Button("Cambia");        cambia.addActionListener(this);
      cambia2=new Button("Bianco");        cambia2.addActionListener(this);
      paSUD=new Panel();                   paSUD.add(new Label("Colore sfondo", Label.RIGHT)); 
                                           paSUD.add(colori);
                                           paSUD.add(cambia); 
                                           paSUD.add(cambia2); 
      paNORD=new Panel(new GridLayout(6, 4)); 
      tRedf=new Label("", Label.CENTER);   paNORD.add(tRedf);
      tRed =new Label("", Label.CENTER);   paNORD.add(tRed);
      tRedH=new Label("", Label.CENTER);   paNORD.add(tRedH);
                                           paNORD.add(new Label("RED")); 
      tGreenf=new Label("", Label.CENTER); paNORD.add(tGreenf); 
      tGreen =new Label("", Label.CENTER); paNORD.add(tGreen); 
      tGreenH=new Label("", Label.CENTER); paNORD.add(tGreenH); 
                                           paNORD.add(new Label("GREEN")); 
      tBluef=new Label("", Label.CENTER);  paNORD.add(tBluef);
      tBlue =new Label("", Label.CENTER);  paNORD.add(tBlue);
      tBlueH=new Label("", Label.CENTER);  paNORD.add(tBlueH);
                                           paNORD.add(new Label("BLUE")); 
                                           paNORD.add(new Label());
      tRGB =new Label("", Label.CENTER);   paNORD.add(tRGB);
      tRGBH=new Label("", Label.CENTER);   paNORD.add(tRGBH);
                                           paNORD.add(new Label("RGB")); 
      tAlphaf=new Label("", Label.CENTER); paNORD.add(tAlphaf);
      tAlpha =new Label("", Label.CENTER); paNORD.add(tAlpha);
      tAlphaH=new Label("", Label.CENTER); paNORD.add(tAlphaH);
                                           paNORD.add(new Label("ALPHA")); 
                                           paNORD.add(new Label());
      tsRGB =new Label("", Label.CENTER);  paNORD.add(tsRGB);
      tsRGBH=new Label("", Label.CENTER);  paNORD.add(tsRGBH);
                                           paNORD.add(new Label("sRGB")); 
      setta(); 
      this.add(paNORD, BorderLayout.NORTH); 
      this.add(tela, BorderLayout.CENTER);
      this.add(paSUD, BorderLayout.SOUTH); 
      this.setSize(400, 350);
      this.setVisible(true);
   }

   public void actionPerformed(ActionEvent e)
   {
      String nome=e.getActionCommand();
      if(nome.equals("Cambia"))
      {
         int scelta=colori.getSelectedIndex();
         sfondo=cCOLORI[scelta];
      }
      else if(nome.equals("Bianco"))
         sfondo=Color.white;
      tela.setBackground(sfondo);
      setta()
   }
   private void setta()
   {
      int Alpha=sfondo.getAlpha(); tAlpha.setText("" + Alpha);
                                   tAlphaH.setText(Integer.toHexString(Alpha).toUpperCase()); 
      int Blue =sfondo.getBlue();  tBlue.setText("" + Blue);
                                   tBlueH.setText(Integer.toHexString(Blue).toUpperCase()); 
      int Green=sfondo.getGreen(); tGreen.setText("" + Green);
                                   tGreenH.setText(Integer.toHexString(Green).toUpperCase()); 
      int Red =sfondo.getRed();    tRed.setText("" + Red);
                                   tRedH.setText(Integer.toHexString(Red).toUpperCase()); 
      int sRGB =sfondo.getRGB();   tsRGB.setText("" + sRGB);
                                   tsRGBH.setText(Integer.toHexString(sRGB).toUpperCase()); 
      int RGB =sRGB & 0x00FFFFFF;  tRGB.setText("" + RGB);
                                   tRGBH.setText(Integer.toHexString(RGB).toUpperCase());
      float[] RGBA=sfondo.getRGBComponents(null);
                                   tRedf.setText("" + RGBA[0]);
                                   tGreenf.setText("" + RGBA[1]);
                                   tBluef.setText("" + RGBA[2]);
                                   tAlphaf.setText("" + RGBA[3]); 
   }
   public static void main(String args[])
   {
      CambiaColore2 cc=new CambiaColore2();
   }
}

1. setta()

2. getAlpha(), getBlue(), getGreen(), getRed(), getRGB(), getRGBComponents()

3. toHexString(), toUpperCase()