Javaサンプル(プルダウン選択とイメージ表示)

//Sample02
import java.awt.Choice;
import java.awt.FlowLayout;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
public class Sample02 extends Frame implements ItemListener {
  private static final String image01_filename = "bk079.jpg";
  private static final String image02_filename = "bk089.jpg";
  private static final String image03_filename = "bk160.jpg";
  private static final String window_title = "プルダウン選択とイメージ表示";
  private static final int position_X = 100;
  private static final int position_Y = 150;
  private static final int window_width = 640;
  private static final int window_height = 400;
  private static final long serialVersionUID = 1L;
  Image img01;
  Image img02;
  Image img03;
  Choice cho;
  int flg_button = 0;
  // 主処理
  public static void main(final String ar[]) {
    final Frame f = new Sample02();
    f.setTitle(Sample02.window_title);
    f.setSize(Sample02.window_width, Sample02.window_height);
    f.setVisible(true);
  }
  // 部品セット
  Sample02() {
    this.setLayout(new FlowLayout());
    this.cho = new Choice();
    this.cho.add("1999");
    this.cho.add("2000");
    this.cho.add("2001");
    this.add(this.cho);
    this.cho.addItemListener(this);
    this.img01 = Toolkit.getDefaultToolkit().getImage(
        Sample02.image01_filename);
    this.img02 = Toolkit.getDefaultToolkit().getImage(
        Sample02.image02_filename);
    this.img03 = Toolkit.getDefaultToolkit().getImage(
        Sample02.image03_filename);
    this.addWindowListener(new WinAdapter());
  }
  // 閉じる
  class WinAdapter extends WindowAdapter {
    @Override
    public void windowClosing(final WindowEvent we) {
      System.exit(0);
    }
  }
  // 描画
  @Override
  public void paint(final Graphics g) {
    if (this.flg_button > -1) {
      g.clearRect(0, 0, Sample02.window_width - 1,
          Sample02.window_height - 1);
    }
    if (this.flg_button == 0) {
      g.drawImage(this.img01, Sample02.position_X, Sample02.position_Y,
          this);
    }
    if (this.flg_button == 1) {
      g.drawImage(this.img02, Sample02.position_X, Sample02.position_Y,
          this);
    }
    if (this.flg_button == 2) {
      g.drawImage(this.img03, Sample02.position_X, Sample02.position_Y,
          this);
    }
  }
  // イベント
  public void itemStateChanged(final ItemEvent ie) {
    final int imgidx = this.cho.getSelectedIndex();
    if (imgidx == 0) {
      this.flg_button = 0;
      this.repaint();
    }
    if (imgidx == 1) {
      this.flg_button = 1;
      this.repaint();
    }
    if (imgidx == 2) {
      this.flg_button = 2;
      this.repaint();
    }
  }
}