java - 为什么绘制类不能与 setDefault LookAndFeel Decorated(true) 一起使用

Question

package Jai;

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


public class tuna extends JFrame{

    tuna(){
        super("Title");
        setLayout(new FlowLayout());

        getContentPane().setBackground(Color.white);
    }

    public void paint(Graphics g){
        super.paint(g);

        g.fillOval(50, 100, 100, 155);      
    }

    public static void main(String[] arg){
        JFrame.setDefaultLookAndFeelDecorated(true);
        tuna obj = new tuna();
        obj.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        obj.setSize(500,500);
        obj.setVisible(true);
    }
}

我有一个JFrame，我使用paint方法在框架上绘制一个椭圆形。每当我尝试最大化或最小化窗口时，通过 Paint() 方法绘制的椭圆就会消失。我希望即使在最大化或最小化框架时，绘制的图形也能保留。

Answer 1

您的问题是为错误的对象覆盖错误的方法。您必须重写主面板的 paintComponent 方法。这是正确的代码:

import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Graphics;

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

public class tuna extends JFrame {
    tuna() {
        super("Title");
        // you need to override the method paintComponent for the main panel
        setContentPane(new JPanel(new FlowLayout()) {
            @Override
            public void paintComponent(Graphics g) {
                super.paintComponent(g);
                g.fillOval(50, 100, 100, 155);
            }
        });
        getContentPane().setBackground(Color.white);
    }

    public static void main(String[] arg) {
        JFrame.setDefaultLookAndFeelDecorated(true);
        tuna obj = new tuna();
        obj.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        obj.setSize(500, 500);
        obj.setVisible(true);
    }
}