paintComponent 正在执行两次

Question

这让我很困扰，我的代码可以运行，但是当我去运行它时，它似乎循环了我的 for 循环两次，谁能帮助我的逻辑？谢谢...

package pkgcirc;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.*;

/*
* Notes:
* Draw 20 circles
* radius/location (x/y/r) all random
* if (circle) is between radii pt (step thru loop) of all values, if its within ,
*  draw it cyan if it overlaps, else black
*  
*/
public class Main extends JPanel {
    int[] radius = new int [3];
    int[] xArray = new int [3];
    int[] yArray = new int [3];

    public Main()
    {       
        Random g = new Random();
        setPreferredSize (new Dimension(300, 200));
        for(int i = 0; i < radius.length; i++)
        {
            radius[i] = g.nextInt(50)+1;
            xArray[i] = g.nextInt(250)+1;
            yArray[i] = g.nextInt(150)+1;
        }
    }

    public void paintComponent(Graphics page)
    {
        super.paintComponent(page);
        for(int i = 0; i < radius.length; i++)
        {
            for (int j = 0; j < radius.length; j++)
            {
                int xpoint1 = xArray[i]+radius[i];
                int ypoint1 = yArray[i]+radius[i];
                int xpoint2 = xArray[j]+radius[j];
                int ypoint2 = yArray[j]+radius[j];
                int radius1 = radius[i];
                int radius2 = radius[j];
                boolean Collide = circlesCollide(xpoint1, ypoint1, radius1, radius2, xpoint2, ypoint2);

                if (i != j && Collide == false)
                {
                    page.setColor(Color.cyan);
                    page.fillOval(xArray[i] ,yArray[i], radius[i], radius[i]);
                    System.out.println("false");
                }
                else{
                    System.out.println("true");
                    page.setColor(Color.black);
                    page.drawOval(xArray[j] ,yArray[j], radius[j], radius[j]);
                }
            }
            System.out.println("BREAK");    
        }
    }

    public boolean circlesCollide(double x1, double y1, double r1, double x2, double y2, double r2){
        return (distance(x1, y1, x2, y2) <= (r1 + r2));
    }

    public double distance(double x1, double y1, double x2, double y2) {
        return Math.sqrt(((x2 - x1) * (x2 - x1)) + ((y2 - y1) * (y2 - y1)));
    }       

    public static void main (String[] args)
    {
        JFrame frame = new JFrame ("Circles");
        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);

        frame.getContentPane().add (new Main());

        frame.pack();
        frame.setVisible(true);
    }
}

Answer 1

调用setPreferredSize() 和pack() 将导致paintComponent() 被调用两次，因为每次调用都需要重新绘制显示。

尝试删除 pack() 并将设置大小移动到底部，如下所示：-

public Main() {
    Random g = new Random();

    //setPreferredSize(...); // commented this line

    for (int i = 0; i < radius.length; i++) {
        radius[i] = g.nextInt(50) + 1;
        xArray[i] = g.nextInt(250) + 1;
        yArray[i] = g.nextInt(150) + 1;
    }
}

public void paintComponent(Graphics page) {
        ...
}

public static void main(String[] args) {
    JFrame frame = new JFrame("Circles");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    frame.setSize(300, 200); // added this line

    frame.getContentPane().add(new Main());

    // frame.pack(); // commented this line

    frame.setVisible(true);
}

现在应该可以正常工作了。

Answer 2

       for(int i = 0; i < radius.length; i++)
       {
           for (int j = 0; j < radius.length; j++)
           {

您希望比较两个元素的每一对的大多数循环都是这样编写的：

       for(int i = 0; i < radius.length; i++)
       {
           for (int j = i; j < radius.length; j++)
           {

（注意第二个循环中的j = i。）

这还可以让您删除i != j 测试。 :)

编辑：糟糕； j = i 表示您仍然需要进行i != j 测试——如果您使用了j = i+1，那么您可以删除i != j 测试。叹。 :)