How can I move focused button?

Question

I have some issues with my Java Swing code.

I want to move between buttons using the keyboard (UP, DOWN key) and press the button using the ENTER key. But I think there is no way to use the keyboard.

Can anyone teach me how to move buttons with the keyboard UP and DOWN keys?
I also have used JRadioButton, but it was difficult...

The below code is my code!

import javax.swing.*;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

public class StartScreen extends JFrame {

  JButton[] buttons;
  private KeyListener playerKeyListener;

  public StartScreen() {
    setTitle("테트리스 시작 화면");

    setSize(400, 500);
    setResizable(false);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setLayout(null);
    setBackground(Color.PINK);

    JPanel jPanel = new JPanel();

    jPanel.setBackground(Color.PINK);
    jPanel.setBounds(0,0,400,500);
    jPanel.setLayout(null);

    String[] btnText = {"일반 모드 게임 시작", "아이템 모드 게임 시작", "게임 설정", "스코어 보드", "게임 종료"};
    buttons = new JButton[5];
    for (int i = 0; i < buttons.length; i++) {
      buttons[i] = new JButton(btnText[i]);
      buttons[i].setBackground(new Color(0,0,0,0));
      buttons[i].setVisible(true);
      buttons[i].setBorderPainted(true);
      jPanel.add(buttons[i]);
    }

    int y = 150;
    for (int i = 0; i < buttons.length; i++) {
      buttons[i].setBounds(125, y, 150, 50);
      y += 60;
    }

    JLabel jLabel = new JLabel("Tetris");
    Font font = new Font("Arial", Font.BOLD, 40);
    jLabel.setFont(font);
    jLabel.setLayout(null);
    jLabel.setBounds(145,80,150,40);
    jPanel.add(jLabel, BorderLayout.CENTER);


    getContentPane().add(jPanel);
    setVisible(true);

    playerKeyListener = new PlayerKeyListener();
    addKeyListener(playerKeyListener);
    setFocusable(true);
    requestFocus();

  }

  public class PlayerKeyListener implements KeyListener {
    @Override
    public void keyTyped(KeyEvent e) {

    }

    @Override
    public void keyPressed(KeyEvent e) {
      switch(e.getKeyCode()) {
        case KeyEvent.VK_DOWN:

          break;
        case KeyEvent.VK_UP:

          break;
        default:
          System.out.println("");
      }
    }

    @Override
    public void keyReleased(KeyEvent e) {

    }
  }

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

}

Answer 1

Following shows two different approaches:

1. add a KeyStroke to the set of focus traversal keys which allows you change the behaviour for a specific component.
2. add a Key Binding to the panel which will then allow you to use the arrow keys for all components on the panel

Choose the approach that best meets your requirment.

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

public class FocusTraversalKeys extends JPanel
{
    public FocusTraversalKeys()
    {
        for (int i = 0; i < 5; i++)
        {
            JButton button = new JButton( String.valueOf(i) );
            add( button );

            //  Add left arrow key as a focus traversal key.
            //  Applies only to this specific component.

            Set<AWTKeyStroke> set = new HashSet<AWTKeyStroke>( button.getFocusTraversalKeys(
                KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS ) );
            set.add( KeyStroke.getKeyStroke( "LEFT" ) );
            button.setFocusTraversalKeys(
                KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS, set );
        }

        //  Add right arrow key as a focus traversal key.
        //  Applies to all components on the panel

        InputMap im = getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT);
        String rightText = "RIGHT";
        im.put(KeyStroke.getKeyStroke(rightText), rightText);
        getActionMap().put(rightText, new AbstractAction()
        {
            @Override
            public void actionPerformed(ActionEvent e)
            {
                KeyboardFocusManager.getCurrentKeyboardFocusManager().focusNextComponent();
            }
        });
    }

    private static void createAndShowGUI()
    {
        JFrame frame = new JFrame("FocusTraversalKeys");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add( new FocusTraversalKeys() );
        frame.setLocationByPlatform( true );
        frame.pack();
        frame.setVisible( true );
    }

    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowGUI();
            }
        });
    }
}