简单打印一个圆形GUI问题

Question

所以我是gui的新手,我想制作一个简单的程序来打印一个圆圈来代表太阳,然后在它附近我想打印另一个圆来代表一个星球.我的问题是当我添加方法paintPlanet时,gui窗口中返回的所有内容现在都是空白屏幕.即使我将paintPlanet评论出来,太阳的圆也不会打印出来,我留下一个空白的窗口.有人可以帮我弄清楚我哪里出错了如何修复它,这样两个圆圈都会打印出来？我是GUI新手,所以对我来说很容易:)

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JPanel;


public class PlanetsLogic extends JPanel
{   
private static final long serialVersionUID = 1L;

public void paintSun(Graphics g)
{
    super.paintComponent(g);

    //create circle and fill it as yellow to represent the sun
    g.setColor(Color.YELLOW);
    g.drawOval(100, 75, 75, 75);
    g.fillOval(100, 75, 75, 75);
} //end paintSun


public void paintPlanet(Graphics g)
{
    super.paintComponent(g);
    //create circle and fill it as yellow to represent the orbiting planet
    g.setColor(Color.BLUE);
    g.drawOval(75, 75, 75, 75);
    g.fillOval(75, 75, 75, 75);


}//end paintPlanet

}//end class PlanetsLogic

主要:

import javax.swing.JFrame;

public class OrbitingPlants_main 
{

public static void main(String[] args) 
{

    PlanetsLogic planet = new PlanetsLogic();
    JFrame frame = new JFrame();

    frame.setTitle("Orbiting Planets");
    frame.setSize(300, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.add(planet); //add panel onto frame
    frame.setVisible(true); 
}

}

Answer 1

您的paintSun和paintPlanet方法永远不会被神奇地调用.相反,您的JPanel需要覆盖paintComponent方法,因为所有绘图都在那里完成.你甚至可以在paintComponent中调用paintSun和paintPlanet方法,但是我建议super.paintComponent(g)只调用一次,只能在paintComponent方法中覆盖它自己.

例如,

// use @Override to ask the compiler to check if this method is a true override
@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g); // HERE!
    paintSun(g);
    paintPlanet(g);
}

public void paintSun(Graphics g) {
    // super.paintComponent(g); // nope, not here!

    //create circle and fill it as yellow to represent the sun
    g.setColor(Color.YELLOW);
    g.drawOval(100, 75, 75, 75);
    g.fillOval(100, 75, 75, 75);
} //end paintSun


public void paintPlanet(Graphics g) {
    // super.paintComponent(g);  // NO don't call this here
    //create circle and fill it as yellow to represent the orbiting planet
    g.setColor(Color.BLUE);
    g.drawOval(75, 75, 75, 75);
    g.fillOval(75, 75, 75, 75);
}//end paintPlanet