java 鼠标简单控制和浮点数在内存中的表示方式

import java.awt.*;import javax.swing.*;import java.awt.event.*;import java.util.*;import java.awt.geom.*;public class MouseTest {public static void main(String[] args){EventQueue.invokeLater(new Runnable(){public void run(){MouseFrame frame = new MouseFrame();frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);frame.setVisible(true);}});}}class MouseFrame extends JFrame{public MouseFrame(){setTitle("MouseTest");setSize(DEFAULT_WIDTH,DEFAULT_HEIGHT);MouseComponent component = new MouseComponent();add(component);}public static final int DEFAULT_WIDTH = 300;public static final int DEFAULT_HEIGHT = 200;}class MouseComponent extends JComponent{public MouseComponent(){squares = new ArrayList<Rectangle2D>();current = null;addMouseListener(new MouseHandler());addMouseMotionListener(new MouseMotionHandler());}public void paintComponent(Graphics g){Graphics2D g2 = (Graphics2D) g;for(Rectangle2D r:squares){g2.draw(r);}}public Rectangle2D find(Point2D p){for(Rectangle2D r:squares){if(r.contains(p))return r;}return null;}public void add(Point2D p){double x = p.getX();double y = p.getY();current = new Rectangle2D.Double(x-SIDELENGTH/2, y-SIDELENGTH/2, SIDELENGTH, SIDELENGTH);squares.add(current);repaint();}public void remove(Rectangle2D s){if(s == null)return;if(s == current)current = null;squares.remove(s);repaint();}private static final int SIDELENGTH = 10;private ArrayList<Rectangle2D> squares;private Rectangle2D current;private class MouseHandler extends MouseAdapter{public void mousePressed(MouseEvent event){current = find(event.getPoint());if(current == null)add(event.getPoint());}public void mouseClicked(MouseEvent event){current = find(event.getPoint());if(current != null && event.getClickCount()>=2)remove(current);}}private class MouseMotionHandler implements MouseMotionListener{public void mouseMoved(MouseEvent event){if(find(event.getPoint()) == null)setCursor(Cursor.getDefaultCursor());else setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));}public void mouseDragged(MouseEvent event){if(current != null){int x = event.getX();int y = event.getY();current.setFrame(x-SIDELENGTH/2,y-SIDELENGTH/2, SIDELENGTH, SIDELENGTH);repaint();}}}}

1. 结合鼠标事件和swing 2D图形技术的简单运用，可以利用鼠标的单击或双击完成相应操作 。

简单功能为，单击鼠标就可以在窗口上出现一个小正方形，双击即可删除，按住可以拖动。

PS：可以利用这些悄悄的写下你心爱的人的名字哦~~虽然字看起来歪歪斜斜的，不过证明心意嘛~~嘿嘿

 

2.浮点数在内存中的表示方式

这个要认真理解，我花了将近一个小时的时间

 

首先是在JDK中了解Float中的intBitsToFloat方法的含义。

s * m * 2^(e-150)

s为符号位，int s = ((bits & 31 ) == 0)? 1:-1      0表示为正。

e表示存储在内存中的23位到31位bits，作为幂指数。 int  e =（bits >> 23) & 0xff           

m表示存储在内存中的0到22位bits，作为有效位。  int m = (e == 0)?  (bits & 0x7fffff) << 1 : (bits & 0x7fffff) | 0x800000;

例如，计算0x50000000的对应的浮点数

s=0;

e  后23位有效位与0xff相与之后结果为 10100000  结果为160

m 与 0x800000相或后结果为2^23

所以结果为2^33

有点混乱，自己认真整理一下就好了