java - 并非所有 JComponent 都被绘制

Question

我有两个扩展 JComponent 的对象，这两个对象都重写 PaintComponent()。当仅将其中之一添加到 Jpanel 时，它会正确绘制，但是如果我添加两者，则仅显示一个。

添加两者的我的初始化方法如下:

public class Applet extends JApplet {

long time_interval = 200; // length of time between moves in ms
int w = 75;
int h = 75;
int[][] a = new int[w][h]; // creates a 2D array to use as background
Creature test;

public void init() {
    System.out.println("Zachary Powell 1104583");
    resize(750, 850);

    WorldView tv = new WorldView(a);
    // add(applet, BorderLayout.CENTER);

    test = new Creature(100, 30, 1);
    add(tv);
    add(test);

    startTimer();
}
...

但是电视没有绘制

我的生物类别:

public class Creature extends JComponent{
    int health;
    boolean dead;
    int xpos, ypos;
    static int size = 10;

    Creature(int h, int y, int x) {
        dead = false;
        health = h;
        ypos = y;
        xpos = x;
    }

    void Update() {
        checkHealth();
    }

    private void checkHealth() {
        if (health <= 0)
            dead = true;
    }

    public void reduceHealth(int amount) {
        health -= amount;
    }

    public void move() {
        if (xpos < 75) {
            xpos++;
        } else {
            xpos = 1;
        }
        reduceHealth(1);
    }

    public void paintComponent(Graphics g) {
        g.setColor(Color.BLUE);
        g.fill3DRect(xpos * size, ypos * size, size, size, true);
    }
}

还有我的 WorldView 类(class)

public class WorldView extends JComponent {
    static Color[] colors =
            {black, green, blue, red,
                    yellow, magenta, pink, cyan};
    int[][] a;
    int w, h;
    static int size = 10;
    //Create the object with the array give
    public WorldView(int[][] a) {
        this.a = a;
        w = a.length;
        h = a[0].length;
    }

    public void paintComponent(Graphics g) {
        for (int i = 0; i < w; i++) {
            for (int j = 0; j < h; j++) {
                    g.fill3DRect(i * size, j * size,
                            size, size, true);
            }
        }
    }

    public Dimension getPreferredSize() {
        return new Dimension(w * size, h * size);
    }
}

Answer 1

顶级容器的默认布局是 BorderLayout。默认情况下，如果您不指定约束，组件将添加到 CENTER。但是，只能将一个组件添加到 CENTER，因此仅显示最后添加的一个组件。

WorldView should be in the backround centred with Creature in the foreground

然后将 WorldView 添加到小程序中，并将 Creature 添加到 WorldView 中。

您需要在 WorldView 上使用适当的布局管理器来获得所需的布局。