java中怎么改变坐标系的位置啊，急急急！
将默认的坐标系改为直角坐标系，y轴向上

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

public class Aloha extends JPanel {

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

        Graphics2D g2d = (Graphics2D)g;

        g2d.translate(getWidth() / 2, getHeight() / 2);
        g2d.scale(1, -1);

        g2d.drawLine(-200, 0, 200, 0);
        g2d.drawLine(0, -200, 0, 200);
        g2d.fillRect(0, 0, 100, 100);
    }

    private static void createAndShowGUI() {
        JFrame frame = new JFrame();

        // Add your component.
        frame.setContentPane(new Aloha());

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(600, 600);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) throws IOException {
        createAndShowGUI();
    }
}