My JPanel won't show up (Java)

Question

I don't understand why my JPanel won't show up since I used pack() and setVisible(true) It just run the application and nothing happens. This is my code

import java.io.*;
import java.net.*;
import java.util.Scanner;
import java.util.concurrent.TimeUnit;

import javax.swing.*;

import java.awt.event.*;
import java.awt.*;

import javax.swing.JFrame;

public class TestGUI extends JFrame {

    private JPanel _panel1 = new JPanel();
    private JTextArea _txtarea = new JTextArea(10, 10);
    private JTextField _txtfield = new JTextField();

    public TestGUI() {
        add(_panel1);
        _panel1.setLayout(new BorderLayout());
        _panel1.add(_txtarea);
        _panel1.add(_txtfield);
        validate();
        _panel1.setVisible(true);
        _panel1.setSize(500, 500);
    }

    public static void main(String[] args) {
        new TestGUI();
    }
}

Answer 1

I suggest showing the JFrame as well, as it contains your JPanel .

Try this as your main()

public static void main(String[] args) {
  SwingUtilities.invokeLater(new Runnable() {
    public void run() {
      new TestGUI().setVisible(true);
    }
  });
}

Answer 2

You have a few issues in your code. You are not setting the Layout correctly. BorderLayout requires positioning.

Once you have added the components to the JFrame, you either set a size for it or call pack() method, so that you JFrame assumes the size needed to fit the subcomponents.

Here is an a sample:

class TestGUI extends JFrame {

        private JPanel _panel1 = new JPanel();
        private JTextArea _txtarea = new JTextArea(10, 10);
        private JTextField _txtfield = new JTextField();

        public TestGUI() {
            add(_panel1);
            _panel1.setLayout(new BorderLayout());

            // border layout is done by positioning like center, south north etc.
            _panel1.add(_txtarea, BorderLayout.CENTER);
            _panel1.add(_txtfield, BorderLayout.NORTH);

            // set the size before making it visible
            _panel1.setSize(500, 500);
            setVisible(true);

            // call pack() so that the Frame assumes the needed space only
            pack();

            // set a default close method so that your frame  exits on close.
           setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        }
    }

Next it is a good practice to spawn your JFrame through SwingUtilities.invokeLater or EventQueue.invokeLater , so that it is handled by the Event Dispatch Thread in it's own good time when processing the queue of events.