JCheckbox不显示

Question

I'm trying to create a java GUI and I'm having some trouble getting my checkboxes to show. I've looked at the oracle tutorial and included all the code they have but I'm not sure what I'm missing. Any ideas?

public class HPAProgram {
    public static void main(String[] args) {
        MapWindow map = new MapWindow();        
    }
}

import java.awt.event.*;
import javax.swing.*;  //notice javax
public class MapWindow extends JFrame
{
    private static final int WIDTH = 600, HEIGHT = 800;

    SettingsButtonsPanel button_panel = new SettingsButtonsPanel();

    public MapWindow()
    {
        setLocationRelativeTo(null);
        setTitle("HPA* Test");
        setSize(WIDTH, HEIGHT);
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        add(button_panel);
    }

}

import java.awt.event.*;

import javax.swing.*;  //notice javax
public class SettingsButtonsPanel extends JPanel implements ItemListener{
    private static final int WIDTH = 600, HEIGHT = 200;
    private static final int NUM_MAP_TYPE = 2;

    private JCheckBox[] map_type;

    JPanel panel = new JPanel();

    public SettingsButtonsPanel(){
        this.setBounds(0,0,WIDTH, HEIGHT);

        map_type = new JCheckBox[NUM_MAP_TYPE];

        map_type[0] = new JCheckBox("Sparse");
        map_type[0].setSelected(true);
        map_type[0].setVisible(true);
        map_type[0].setLocation(0,0);
        map_type[0].setSize(100,100);


        map_type[1] = new JCheckBox("Maze");
        map_type[1].setSelected(false);

        for(int i = 0; i < NUM_MAP_TYPE; i++)
            map_type[i].addItemListener(this);
    }

    public void itemStateChanged(ItemEvent e)
    {
        Object source = e.getItemSelectable();
        //if(source == )
    }
}

Answer 1

for(int i = 0; i < NUM_MAP_TYPE; i++) {
        map_type[i].addItemListener(this);
        this.add(map_type[i]);
}

But it's better to use a LayoutManager (eg BoxLayout) for the panel.