Java Не отображаются кнопки

[teacher future]

Здравствуйте! очень сильно нужна помощь . Не отображаются кнопки

package com.company;
import com.company.HangmanFrame;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.lang.*;
//import.awt.event.ActionEvent;
//import java.awt.event.ActionListener;
public class Main {

    public static void main(String[] args) {
  HangmanFrame frame = new HangmanFrame() {
      @Override
      public void actionPerformed(ActionEvent e) {

      }
  };

        }
    }

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package com.company;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.lang.*;

abstract class HangmanFrame implements ActionListener {
    JLabel out = new JLabel("Виселица");
    String key[] = {"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"};

    HangmanFrame() {
        JFrame j1 =new JFrame("Виселица");
        j1.setSize(600, 600);
        j1.getContentPane().setLayout(new FlowLayout());
        j1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        out.setBorder(BorderFactory.createEtchedBorder());
        j1.getContentPane().add(out);
        JButton key_button[] = new JButton[26];

        for (char i = 'a'; i <= 'z'; i++) {
            key_button[i] = new JButton(key[i]);
            j1.getContentPane().add(key_button[i]);
            key_button[i].addActionListener(this);
        }
        j1.setVisible(true);
    }

    public void actionPerformed(ActiveEvent e) {
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new HangmanFrame() {
                    @Override
                    public void actionPerformed(ActionEvent e) {

                    }
                };
            }
        });
    }
}