java 如何在java中画一条线？
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How to draw a line in java?
提问by sebkur
I want to draw a line in java in eclipse. I made this code but I am getting error in line : paint2d.add(paintComponent());
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);
}
}
How to fix that error?
如何修复该错误？
Is my code suitable for the purpose of drawing a line?
我的代码适合画线吗？
Thanks.
谢谢。
回答by sebkur
You're not overriding the method correctly. The argument to paintComponentis of type Graphics, not Graphics2D, but you can cast to Graphics2D. Also you need to add the Gamepanel to the frame as a content pane:
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();
}
}
回答by johnrobert
There are two errors in your code/approach:
您的代码/方法中有两个错误：
- The method paintComponenthas a Graphicsas parameter, not a Graphics2D.
- Game is a JPanel and must be added into the JFrame to be shown.
- 方法paintComponent有一个Graphics作为参数，而不是Graphics2D。
- Game 是一个 JPanel，必须添加到 JFrame 中才能显示。
The source code below solves the problems.
下面的源代码解决了这些问题。
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);
}
}
