16.23

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

public class Test_16_23 extends JFrame{
    private ArrayList xArray = new ArrayList();
    private ArrayList yArray = new ArrayList();
    
    private  int  xPoint,yPoint;
    private int radius = 5;
    private boolean draw = false;
    
    public Test_16_23(){
        add(new JP());
    }
    
    public static void main(String[] args) {
        JFrame frame = new Test_16_23();
        frame.setTitle("Test_16_23");
        frame.setSize(300, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
      }
    
    class JP extends JPanel{
        private int x1,y1,x2,y2;
        
        public JP(){
            addMouseListener(new MouseAdapter(){
                public void mouseClicked(MouseEvent e){
                    xPoint = e.getX();
                    yPoint = e.getY();
                    draw = true;
                    xArray.add(xPoint);
                    yArray.add(yPoint);
                    
                    repaint();
                }
            });
        }
        
        protected void paintComponent(Graphics g){
            super.paintComponent(g);
            
            for(int i = 0; i < xArray.size(); i++){                
            if(draw)
            //画空心圈
            g.drawOval((Integer.parseInt(xArray.get(i).toString()))-radius,(Integer.parseInt(yArray.get(i).toString()))-radius, 2*radius, 2*radius);
            }
            //如果点超过2个，再填充            
            if(xArray.size() > 1)
                {                       
                    findTheNearest();
                    g.fillOval((Integer.parseInt(xArray.get(x1).toString()))-radius,(Integer.parseInt(yArray.get(y1).toString()))-radius, 2*radius, 2*radius);
                    g.fillOval((Integer.parseInt(xArray.get(x2).toString()))-radius,(Integer.parseInt(yArray.get(y2).toString()))-radius, 2*radius, 2*radius);
                }
            
        }
        
        public void findTheNearest(){
            //第一对点赋值           
            x1 = y1 = 0;
            x2 = y2 = 1;
            double Value = 0;
            double minValue = theDistance(Integer.parseInt(xArray.get(0).toString()),Integer.parseInt(yArray.get(0).toString()),
                    Integer.parseInt(xArray.get(1).toString()),Integer.parseInt(yArray.get(1).toString()));
            //利用两层循环达到遍历所有点间距的目的
            for(int i = 0; i < xArray.size(); i++){
                for(int j = i + 1; j < xArray.size(); j++){
                Value = theDistance(Integer.parseInt(xArray.get(i).toString()),Integer.parseInt(yArray.get(i).toString()),Integer.parseInt(xArray.get(j).toString()),
                        Integer.parseInt(yArray.get(j).toString()));
                    if(Value < minValue)
                    {                        
                        minValue = Value;
                        x1 = y1 = i;
                        x2 = y2 = j;
                    }    
                }           
            }
        }
        
        public double theDistance(int x1, int y1, int x2, int y2){
            return Math.sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
        }
    }    
}

效果图：