如何生成随机数

对于如何生成随机数一般有以下几个方法

1.直接调用Math.random()函数

 int x=(int)(Math.random()*6)——生成0-5的随机数

import javax.swing.JOptionPane;

public class RandomInt {
   public static void main( String args[] )
   {
      int value;
      String output = "";

      for ( int i = 1; i <= 20; i++ ) {
         value = 1 + (int) ( Math.random() * 6 );
         output += value + "  ";
         
         if ( i % 5 == 0 )
            output += "\n";
      }

      JOptionPane.showMessageDialog( null, output,
         "20 Random Numbers from 1 to 6",
         JOptionPane.INFORMATION_MESSAGE );

      System.exit( 0 );
   }
}

2.JDK提供了Random类

import java.util.Random

Random r=new Random();

int x=r.nextInt(100)+1生成一个1到101的随机数

import java.util.*;

public class TestRandom
{
    public static void main(String[] args) 
    {
        Random rand = new Random();
        System.out.println("rand.nextBoolean()：" + rand.nextBoolean());
        byte[] buffer = new byte[16];
        rand.nextBytes(buffer);
        System.out.println(Arrays.toString(buffer));
        //生成0.0~1.0之间的伪随机double数
        System.out.println("rand.nextDouble()：" + rand.nextDouble());
        //生成0.0~1.0之间的伪随机float数
        System.out.println("rand.nextFloat()：" + rand.nextFloat());
        //生成平均值是 0.0，标准差是 1.0的伪高斯数
        System.out.println("rand.nextGaussian()：" + rand.nextGaussian());
        //生成一个处于long整数取值范围的伪随机整数
        System.out.println("rand.nextInt()：" + rand.nextInt());
        //生成0~26之间的伪随机整数
        System.out.println("rand.nextInt(26)：" + rand.nextInt(26));
        //生成一个处于long整数取值范围的伪随机整数
        System.out.println("rand.nextLong()：" +  rand.nextLong());
    }
}

3.带种子的随机数

import java.util.Random;

public class TestSeed
{
    public static void main(String[] args)
    {
        Random r1 = new Random(50);
        System.out.println("第一个种子为50的Random对象");
        System.out.println("r1.nextBoolean():\t" + r1.nextBoolean());
        System.out.println("r1.nextInt():\t\t" + r1.nextInt());
        System.out.println("r1.nextDouble():\t" + r1.nextDouble());
        System.out.println("r1.nextGaussian():\t" + r1.nextGaussian());
        System.out.println("---------------------------");
        
        Random r2 = new Random(50);
        System.out.println("第二个种子为50的Random对象");
        System.out.println("r2.nextBoolean():\t" + r2.nextBoolean());
        System.out.println("r2.nextInt():\t\t" + r2.nextInt());
        System.out.println("r2.nextDouble():\t" + r2.nextDouble());
        System.out.println("r2.nextGaussian():\t" + r2.nextGaussian());
        System.out.println("---------------------------");
        
        Random r3 = new Random(100);
        System.out.println("种子为100的Random对象");
        System.out.println("r3.nextBoolean():\t" + r3.nextBoolean());
        System.out.println("r3.nextInt():\t\t" + r3.nextInt());
        System.out.println("r3.nextDouble():\t" + r3.nextDouble());
        System.out.println("r3.nextGaussian():\t" + r3.nextGaussian());
        
       
        Random r4 = new Random(System.currentTimeMillis());
        System.out.println("以当前时间为种子的Random对象");
        System.out.println("r3.nextBoolean():\t" + r4.nextBoolean());
        System.out.println("r3.nextInt():\t\t" + r4.nextInt());
        System.out.println("r3.nextDouble():\t" + r4.nextDouble());
        System.out.println("r3.nextGaussian():\t" + r4.nextGaussian()); 
    }
}

生成以时间为种子的随机数

Random r4 = new Random(System.currentTimeMillis());