Question

如何在没有类（扩展JFrame）的情况下绘制对象？我找到了getGraphics方法，但它没有绘制对象。

import javax.swing.*;
import java.awt.*;
public class Main {
    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        frame.setSize(600, 400);

        JPanel panel = new JPanel();
        frame.add(panel);

        Graphics g = panel.getGraphics();
        g.setColor(Color.BLUE);
        g.fillRect(0, 0, 100, 100);
    }
}

Answer 1

如果要更改绘制组件的方式（添加矩形），则需要在该组件中重新定义paintComponent()。在您的代码中，您使用的是getGraphics()。

您不应该在组件上调用getGraphics()。您所做的任何绘画（对于返回的Graphics）都是临时的，并且在下次Swing确定需要重新绘制组件时将丢失。

相反，您应该覆盖paintComponent(Graphics)方法（JComponent或JPanel），并使用收到的Graphics对象作为参数在此方法中进行绘制

检查this link以便进一步阅读。

以下是您的代码，已更正。

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

public class Main {
    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        frame.setSize(600, 400);

        JPanel panel = new JPanel() {
            @Override
            public void paintComponent(Graphics g) {
                super.paintComponent(g);
                g.setColor(Color.BLUE);
                g.fillRect(0, 0, 100, 100);
            }
        };
        frame.add(panel);

        // Graphics g = panel.getGraphics();
        // g.setColor(Color.BLUE);
        // g.fillRect(0, 0, 100, 100);

        frame.validate(); // because you added panel after setVisible was called
        frame.repaint(); // because you added panel after setVisible was called
    }
}

另一个版本，完全相同，但您可能更清楚：

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

public class Main {
    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        frame.setSize(600, 400);

        JPanel panel = new MyRectangleJPanel(); // changed this line
        frame.add(panel);

        // Graphics g = panel.getGraphics();
        // g.setColor(Color.BLUE);
        // g.fillRect(0, 0, 100, 100);

        frame.validate(); // because you added panel after setVisible was called
        frame.repaint(); // because you added panel after setVisible was called
    }
}

/* A JPanel that overrides the paintComponent() method and draws a rectangle */
class MyRectangleJPanel extends JPanel {
    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.BLUE);
        g.fillRect(0, 0, 100, 100);
    }
}

Answer 2

您必须覆盖JPanel类中的paintComponent方法。因此，您应该创建一个扩展JPanel并在子类

中覆盖paintComponent方法的类

Answer 3

java.awt.image.BufferedImage中

为什么不使用java.awt.image.BufferedImage的实例？ e.g。

BufferedImage output = new BufferedImage(600, 400, BufferedImage.TYPE_INT_RGB);

Graphics2D g2 = output.createGraphics();
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
    RenderingHints.VALUE_ANTIALIAS_ON);
g2.setColor(Color.WHITE);
g2.fillRect(0, 0, output.getWidth(), output.getHeight());
g2.setColor(Color.BLUE);
g2.fillRect(0, 0, 100, 100);

JOptionPane.showMessageDialog(null, new ImageIcon(output));

使用getGraphics（）绘制对象而不扩展JFrame

3 个答案:

java.awt.image.BufferedImage中