Javaサンプル(ボタンクリックと文字列表示)

//Sample21
import java.applet.Applet;
import java.awt.Button;
import java.awt.Label;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class Sample21 extends Applet implements ActionListener {
   private static final String labelTitle = "ボタンクリックで文字列表示";
  private static final String b0_title = "1999";
  private static final String b1_title = "2000";
  private static final String b2_title = "2001";
  private static final int windowWidth = 320;
  private static final int windowHeight = 200;
  private static final int drawX = 100;
  private static final int drawY = 150;
  private static final long serialVersionUID = 1L;
  Button b0;
  Button b1;
  Button b2;
    int swithCode=-1;
    //初期処理
    @Override
  public void init(){
        this.setSize(Sample21.windowWidth,Sample21.windowHeight);
        this.add(new Label(Sample21.labelTitle));
        this.b0=new Button(Sample21.b0_title);
        this.b1=new Button(Sample21.b1_title);
        this.b2=new Button(Sample21.b2_title);
        this.add(this.b0);
        this.add(this.b1);
        this.add(this.b2);
        this.b0.addActionListener(this);
        this.b1.addActionListener(this);
        this.b2.addActionListener(this);
    }
    //描画
    @Override
  public void paint(final Graphics g){
        final String s0="あああああ";
        final String s1="いいいいいいいいい";
        final String s2="ううう";
        if(this.swithCode>-1){
            g.clearRect(0,0,Sample21.windowWidth-1,Sample21.windowHeight-1);
        }
        if(this.swithCode==0){
            g.drawString(s0,Sample21.drawX,Sample21.drawY);
        }
        if(this.swithCode==1){
            g.drawString(s1,Sample21.drawX,Sample21.drawY);
        }
        if(this.swithCode==2){
            g.drawString(s2,Sample21.drawX,Sample21.drawY);
        }
    }
    //イベント
    public void actionPerformed(final ActionEvent ae){
        if(ae.getSource()==this.b0){
            this.swithCode=0;
            this.repaint();
        }
        if(ae.getSource()==this.b1){
            this.swithCode=1;
            this.repaint();
        }
        if(ae.getSource()==this.b2){
            this.swithCode=2;
            this.repaint();
        }
    }
}