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Math.random()是令系统随机选取大于等于 0.0 且小于 1.0 的伪随机 double 值，是Java语言常用代码。
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例如：var a:Number=Math.random()*2+1，设置一个随机1到3的变量。
我自己做的系统里面用作验证码的JSP的
%@page contentType="image/jpeg;charset=utf-8"%
%@page import="java.util.*,java.awt.*,java.awt.image.*,javax.imageio.*" %
%@ page import="java.io.OutputStream" %
html
body
%!
Color getRandColor(int fc,int bc)
{
Random rd=new Random();
if(fc255) fc=255;
if(bc255) bc=255;
int red=fc+rd.nextInt(bc-fc);
int green=fc+rd.nextInt(bc-fc);
int blue=fc+rd.nextInt(bc-fc);
return new Color(red,green,blue);
}
%
%
Random r=new Random();
response.addHeader("Pragma","No-cache");
response.addHeader("Cache-Control","no-cache");
response.addDateHeader("expires",0);
int width=90;
int height=23;
BufferedImage pic=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
Graphics gc=pic.getGraphics();
gc.setColor(getRandColor(200,250));
gc.fillRect(0,0,width,height);
String[] rNum ={"0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f",
"g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w",
"x","y","z","A","B","C","D","E","F","G","H","I","J","K","L","M","N",
"O","P","Q","R","S","T","U","V","W","X","Y","Z"};
int[] style = {Font.PLAIN,Font.BOLD,Font.ITALIC,Font.PLAIN+Font.BOLD,
Font.BOLD+Font.ITALIC,Font.PLAIN+Font.ITALIC,Font.PLAIN+Font.BOLD+Font.ITALIC};
gc.setColor(Color.WHITE);
gc.drawLine(0,30,90,10);
gc.setColor(getRandColor(160,200));
for (int i=0;i50;i++)
{
int x = r.nextInt(width);
int y = r.nextInt(height);
int xl = r.nextInt(10);
int yl = r.nextInt(10);
gc.drawLine(x,y,x+xl,y+yl);
}
gc.setColor(getRandColor(60,150));
String rt = "";
for(int i=0;i4;i++){
String temp = rNum[r.nextInt(62)];
rt = rt+temp;
gc.setFont(new Font("Times New Roman",style[r.nextInt(7)],15));
gc.drawString(temp,5+i*15+r.nextInt(10),10+r.nextInt(10));
}
gc.dispose();
session.setAttribute("randNum",rt);
OutputStream os=response.getOutputStream();
ImageIO.write(pic,"JPEG",os);
System.out.println("当前验证码为:"+session.getAttribute("randNum"));
os.flush();
os.close();
os=null;
response.flushBuffer();
out.clear();
out = pageContext.pushBody();
%
/body
/html
import java.util.*;
public class RandomStudentId{
private int studentID;
private Random rand = new Random();
//private Set s = new HashSet();
public void RandID(){
studentID = rand.nextInt(1000); //这里写多少，就是从0到多少的随机数字
}
public int getID(){
return studentID;
}
public String toString(){
return "Student ID: " + studentID;
}
public static void main(String[] args){
RandomStudentId rsi = new RandomStudentId();
for(int i=0; i100; ++i){
rsi.RandID();
System.out.println("NO." + rsi.getID());
}
}
}
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
public class SelectNo {
public static void main(String[] args) {
//将1-35号码放入List集合
ListString list = new ArrayListString();
for (int i = 1; i 36; i++) {
list.add(""+i);
}
//新建一个List集合用来存放抽出来的号码
ListString newList = new ArrayListString();
//随机抽取list集合中的一个元素，抽出后删除
Random rd = new Random();
int count = list.size();//集合中剩余号码
while (count 0) {
int index = rd.nextInt(count);//抽出的号码的位置
//放入新的集合
newList.add(list.get(index));
//删除原有集合的元素
list.remove(index);
count--;//原有集合少了一个
}
//输出号码
for (int i = 0; i newList.size(); i++) {
System.out.print(newList.get(i)+"\t");
//每五个换行
if(i%5 == 4){
System.out.println("");
}
}
}
}