The method add(Component) is not applicable for the arguments

Question

I am trying to add a panel to my frame, but it keeps giving me one error that I don't seem to understand.

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);
    } 
}

Your code seems to work for me. Are these two classes in their own files? In the same package? Can you post the full error message with your question? — Hovercraft Full Of Eels, Apr 30 '17 at 14:02
Working well for me too. Please provide more info about your error. — Nikolas Charalambidis, Apr 30 '17 at 14:03
@HovercraftFullOfEels These are two classes in the same package (default package) This is the full error message "Multiple markers at this line - Debug Current Instruction Pointer - The method add(Component) in the type Container is not applicable for the arguments (TestPanel)" — Alkida Osmani, Apr 30 '17 at 14:08
OK, do you have your **own** class nearby that you've named `JPanel`?? — Hovercraft Full Of Eels, Apr 30 '17 at 14:09
OK, what happens if you place a `@Override` annotation above your `paintComponent` method (which should be `protected`, not `public` by the way)? — Hovercraft Full Of Eels, Apr 30 '17 at 14:14

score 2 · Answer 1 · edited May 23 '17 at 12:02

This complete, working example, based on your code, suggests that the problem is in your build environment. In addition,

JFrame::add() forwards to the contend pane implicitly.
Construct and manipulate Swing GUI objects only on the event dispatch thread.
Don't use setSize() when you really mean to override getPreferredSize().
Invoke super.paintComponent() to avoid visual artifacts.
For convenience in testing, a private static class is semantically equivalent to a package-private class.

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);
        }
    }
}

The method add(Component) is not applicable for the arguments

1 Answers1