java方法add（Component）不适用于参数

Question

我试图添加一个面板到我的框架，但它一直给我一个错误，我似乎不明白

Multiple markers at this line
    - Debug Current Instruction Pointer
    - The method add(Component) in the type Container is
      not applicable for the arguments (TestPanel)

import javax.swing.*;

public class FrameTest3 {

    public static void main(String[] args) {
        TestPanel samplePanel=new TestPanel();
        JFrame sampleFrame = new JFrame();
        sampleFrame.getContentPane().add(samplePanel);
        sampleFrame.setSize(300,200);
        sampleFrame.setVisible(true);
        System.out.println("Done");
    } 
}

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

public class TestPanel extends JPanel {

    public void paintComponent(Graphics g) {   
        g.setColor(Color.red);
        g.drawString("hello", 30, 80);
    } 
}

Answer 1

这个完整的工作示例基于您的代码，表明问题出在您的构建环境中。此外

• JFrame::add()隐式转发到竞争窗格

• 在event dispatch thread上构造和操作Swing GUI对象仅

• 当你真的想覆盖^{}时，不要使用setSize()

• 调用super.paintComponent()以避免visual artifacts

• 为了便于测试，一个private static类在语义上等同于一个package-private类

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

public class FrameTest3 {

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> {
            TestPanel samplePanel = new TestPanel();
            JFrame sampleFrame = new JFrame();
            sampleFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            sampleFrame.add(samplePanel);
            sampleFrame.pack();
            sampleFrame.setVisible(true);
            System.out.println("Done");
        });
    }

    private static class TestPanel extends JPanel {

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setColor(Color.red);
            g.drawString("hello", 30, 80);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(300, 200);
        }
    }
}