如何在java中画一条线？

Question

我想在eclipse中用java画一条线。我制作了这段代码，但出现错误：paint2d.add(paintComponent());

import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Game extends JPanel {

    public void paintComponent (Graphics2D g) {
        Graphics2D g2 = (Graphics2D) g;
        g2.drawLine(30, 40, 80, 100);
    }

    public static void main(String[] args) {

        JFrame frame = new JFrame();
        frame.setSize(400, 420);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Game paint2d = new Game();
        paint2d.add(paintComponent()); // The method paintComponent(Graphics2D) in the type Game is not applicable for the arguments ()
        frame.setVisible(true);
    }
}

如何修复该错误？

我的代码适合画线吗？

谢谢。

Answer 1

您没有正确覆盖该方法。to 的参数paintComponent类型为Graphics，不是Graphics2D，但您可以强制转换为Graphics2D。您还需要将Game面板作为内容窗格添加到框架中：

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class Game extends JPanel
{

    @Override
    public void paintComponent(Graphics g)
    {
        Graphics2D g2 = (Graphics2D) g;
        g2.setColor(Color.BLACK);
        g2.drawLine(30, 40, 80, 100);
    }

    public static void main(String[] args)
    {
        JFrame frame = new JFrame();
        frame.setSize(400, 420);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        Game game = new Game();
        frame.setContentPane(game);

        frame.setVisible(true);
        frame.invalidate();
    }

}