除非我调整JFrame的大小，否则图像不会出现

Question

I have been trying to show a image on an JFrame using a JPanel but the image only shows up if I resize the JFrame

Display:

package display;

import javax.swing.JFrame;
import img.*;

public class Screen extends JFrame{

    private static final long serialVersionUID = 1L;

    Spaceship s = new Spaceship();
    public static void main(String[]args){
    new Screen();
    }

    public Screen(){
    setTitle("Spaceships!");
    setSize(700,605);
    setLocationRelativeTo(null);
    add(s);

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);

    }
}

Spaceship

package img;

import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;

import javax.swing.JPanel;

public class Spaceship extends JPanel{

    private static final long serialVersionUID = 1L;

    Image spaceship = (Image)Toolkit.getDefaultToolkit().getImage(getClass().getResource("res/spaceship.png"));

    public void paintComponent(Graphics g){
        super.paintComponent(g);
        g.drawImage(spaceship,100,100,null);
    }
} 

I have know clue whats going on so any help I get would be appreciated

Answer 1

Toolkit.createImage() load images asynchronously. Try specifying image observer. JPanel implements ImageObserver so can use the following line:

g.drawImage(spaceship, 100, 100, this);

As an alternative, you can use ImageIO.read which load images synchronously.

Answer 2

According to the JFrame Tutorial they recommend doing either pack or setSize just before you set visible. How about changing the order of add and setSize?

public Screen(){
    setTitle("Spaceships!");
    setLocationRelativeTo(null);
    add(s);
    setSize(700,605);

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);

}