无法使用OverlayLayout将对象置于另一个对象的顶部

Question

我正在尝试建立塔防游戏。现在我已经完成了类Map（带有怪物通过路径的地图）和Creep类（通过地图的怪物）。

creep对象应位于地图对象的顶部。但是蠕变对象现在正在地图后面移动并且完全不可见。我试图在类Creep的paintComponent（）中改变g.fillOval（）的参数，我确信蠕变正在落后。

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

public class Test2
{
    public static void main(String[] args)
    {
        JFrame frame = new JFrame("TEST_MAP");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel(){
            public boolean isOptimizedDrawingEnabled(){
                return false;
            }
        };
        LayoutManager overlay = new OverlayLayout(panel);
        panel.setLayout(overlay);
        Map testMap = new Map();
        panel.add(testMap);
        Creep red = new Creep(testMap);
        panel.add(red);
        frame.add(panel, BorderLayout.CENTER);

        frame.setSize(400, 400);
        frame.setVisible(true);
    }
}


class Map extends JComponent
{
    static final int largeGrid = 50;
    int[][] path = new int[2][];

    public Map()
    {
        path[0] = new int[] {0, 2, 2, 5, 5, 7};
        path[1] = new int[] {1, 1, 6, 6, 2, 2};
    }

    public void paintComponent(Graphics g)
    {
        g.setColor(Color.GRAY);
        for(int i = 0; i < 6 - 1; i++)
        {
            if(path[0][i] == path[0][i + 1]) //Vertical
                g.fillRect(
                Math.min(path[0][i], path[0][i + 1]) * largeGrid - largeGrid / 2, 
                Math.min(path[1][i], path[1][i + 1]) * largeGrid - largeGrid / 2, 
                largeGrid, 
                Math.abs(line(i)[2] - line(i)[1]) * largeGrid + largeGrid);
            else //Horizontal
                g.fillRect(
                Math.min(path[0][i], path[0][i + 1]) * largeGrid - largeGrid / 2, 
                Math.min(path[1][i], path[1][i + 1]) * largeGrid - largeGrid / 2, 
                Math.abs(line(i)[2] - line(i)[1]) * largeGrid + largeGrid, 
                largeGrid);
        }
    }

    public int[] line(int i)
    {
        int[] temp = new int[3];
        if(path[0][i] == path[0][i + 1])
        {
            temp[0] = path[0][i]; //Longitudinal coordinate
            temp[1] = path[1][i];
            temp[2] = path[1][i + 1];
        } else
        {
            temp[0] = path[1][i];
            temp[1] = path[0][i];
            temp[2] = path[0][i + 1];
        }
        return temp;
    }
}

class Creep extends JComponent implements Runnable
{
    public static final int diameter = 30;
    int hp, speed, posX, posY;
    Thread t = new Thread(this);
    Map m;

    public Creep(Map m)
    {
        this.m = m;
        posX = m.path[0][0] * Map.largeGrid;
        posY = m.path[1][0] * Map.largeGrid;
        t.start();
    }

    public Creep(int hp, int speed, Map m)
    {
        this(m);
        this.hp = hp;
        this.speed = speed;
    }
    public void paintComponent(Graphics g)
    {

        g.setColor(Color.RED);
        g.fillOval(posX - diameter / 2, posY - diameter / 2, diameter, diameter);
    }

    public void walk() throws InterruptedException
    {
        for(int i = 0; i < m.path[0].length - 1; i++)
        {
            if(m.path[0][i] == m.path[0][i + 1]) //Vertical
            {
                while(posY != m.path[1][i + 1] * Map.largeGrid)
                {
                    if(m.path[1][i] < m.path[1][i + 1])
                        posY++;
                    else
                        posY--;
                    repaint();
                    t.sleep(5);
                }
            } else //Horizontal
            {
                while(posX != m.path[0][i + 1] * Map.largeGrid)
                {
                    if(m.path[0][i] < m.path[0][i + 1])
                        posX++;
                    else
                        posX--;
                    repaint();
                    t.sleep(5);
                }
            }
        }
    }

    public void run()
    {
        try
        {
            walk();
        } catch(InterruptedException ie)
        {
        }
    }
}