如何在java中画一条线？

Question

我想在eclipse中画一条线java。我编写了这段代码，但在行中出现错误：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？

我的代码适合画线的目的吗？

谢谢。

Answer 1

您没有正确覆盖该方法。 paintComponent 的参数是 Graphics 类型，而不是 Graphics2D，但您可以转换为 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();
    }

}

Answer 2

您的 code/approach 中有两个错误：

方法 paintComponent 有一个 Graphics 作为参数，而不是 Graphics2D.
游戏是一个 JPanel，必须添加到 JFrame 中才能显示。

下面的源代码解决了问题。

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

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

public class Game extends JPanel {

    public void paintComponent (Graphics 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);

        // Adds Game panel into JFrame
        frame.add(new Game());

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

如何在java中画一条线？

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