JPanelで描画処理 | Codetter（こーどったー）

import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Sample {

	public static void main(String[] args) {
		JPanel panel = new JPanel() {
			@Override
			public void paintComponent(Graphics g) {
				/* paintComponent内に描画処理 */
				g.drawLine(40, 20, 20, 80);
				g.drawLine(20, 80, 80, 80);
				g.drawLine(80, 80, 40, 20);
			}
		};

		JFrame frame = new JFrame();
		frame.getContentPane().add(panel);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setBounds(20, 20, 100, 120);
		frame.setVisible(true);
	}

}