Java:paintComponent() Oval 未出现在 Netbeans 中

Question

我正在尝试学习如何在java中绘制椭圆形，但是我制作的paintComponent没有被任何东西调用，并且尝试调用它只会导致更多问题。

程序运行成功，但我想要显示的图像没有显示。

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


public class TEST2{
public void paintComponent(Graphics g){
    g.drawOval(70, 70, 100, 100);
}
public static void main(String[] args) {
    TEST2 gui = new TEST2();
    gui.setUpFrame();
}   
public void setUpFrame(){
    JFrame frame = new JFrame();
    frame.setTitle("Images should be in this program");
    frame.setSize(600,300);
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}    

}

Answer 1

首先查看 Painting in AWT and Swing和 Performing Custom Painting

为了能够在 Swing 中执行自定义绘制，您必须...

1. 继承自基于 swing 的组件(例如 JComponent 或 JPanel)
2. 然后您必须重写它的 paintComponent 方法并在此方法中执行自定义绘制。
3. 将此组件添加到可显示的内容中(例如 JFrame)

您应该确保在进行任何自定义绘画之前调用super.paintComponent

为了确保您不会犯任何(常见)错误，您应该使用 @Override 注释

举个例子...

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test2 extends JPanel {

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawOval(70, 70, 100, 100);
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(200, 200);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame();
                frame.setTitle("Images should be in this program");
                frame.add(new Test2());
                frame.pack();
                frame.setVisible(true);
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            }
        });
    }

}