本文來(lái)自CSDN博客http://blog.csdn.net/pointbin/archive/2006/01/12/576957.aspx

 
在java.lang.Math中有個(gè)Math.random()方法，它可以產(chǎn)生0-1之間（包括0但不包括1）的任意小數(shù)


在Java中我們可以使用java.util.Random類(lèi)來(lái)產(chǎn)生一個(gè)隨機(jī)數(shù)發(fā)生器。它有兩種形式的構(gòu)造函數(shù)，分別是Random()和Random(long seed)。Random()使用當(dāng)前時(shí)間即System.currentTimeMillis()作為發(fā)生器的種子，Random(long seed)使用指定的seed作為發(fā)生器的種子。

        隨機(jī)數(shù)發(fā)生器(Random)對(duì)象產(chǎn)生以后，通過(guò)調(diào)用不同的method：nextInt()、nextLong()、nextFloat()、nextDouble()等獲得不同類(lèi)型隨機(jī)數(shù)。

       1>生成隨機(jī)數(shù)
           Random random = new Random();
           Random random = new Random(100);//指定種子數(shù)100
           random調(diào)用不同的方法，獲得隨機(jī)數(shù)。
           如果2個(gè)Random對(duì)象使用相同的種子（比如都是100），并且以相同的順序調(diào)用相同的函數(shù)，那它們返回值完全相同。如下面代碼中兩個(gè)Random對(duì)象的輸出完全相同
          import java.util.*;
          class TestRandom {
                public static void main(String[] args) {
                     Random random1 = new Random(100);
                     System.out.println(random1.nextInt());
                     System.out.println(random1.nextFloat());
                     System.out.println(random1.nextBoolean());
                     Random random2 = new Random(100);
                     System.out.println(random2.nextInt());
                     System.out.println(random2.nextFloat());
                     System.out.println(random2.nextBoolean());
                }
            }

        2>指定范圍內(nèi)的隨機(jī)數(shù)
             隨機(jī)數(shù)控制在某個(gè)范圍內(nèi),使用模數(shù)運(yùn)算符%
            import java.util.*;
                 class TestRandom {
                      public static void main(String[] args) {
                           Random random = new Random();
                           for(int i = 0; i < 10;i++) {
                               System.out.println(Math.abs(random.nextInt())%10);
                           }
                      }
                 }
             獲得的隨機(jī)數(shù)有正有負(fù)的，用Math.abs使獲取數(shù)據(jù)范圍為非負(fù)數(shù)

       3>獲取指定范圍內(nèi)的不重復(fù)隨機(jī)數(shù)
            import java.util.*;
            class TestRandom {
                  public static void main(String[] args) {
                       int[] intRet = new int[6];
                       int intRd = 0; //存放隨機(jī)數(shù)
                       int count = 0; //記錄生成的隨機(jī)數(shù)個(gè)數(shù)
                       int flag = 0; //是否已經(jīng)生成過(guò)標(biāo)志
                       while(count<6){
                            Random rdm = new Random(System.currentTimeMillis());
                            intRd = Math.abs(rdm.nextInt())%32+1;
                            for(int i=0;i<count;i++){
                                if(intRet[i]==intRd){
                                    flag = 1;
                                    break;
                                }else{
                                    flag = 0;
                                }
                            }
                            if(flag==0){
                                intRet[count] = intRd;
                                count++;
                            }
                   }
                  for(int t=0;t<6;t++){
                      System.out.println(t+"->"+intRet[t]);
                  }
               }
            }