Java Java.util.Random用法及代碼示例

java中Random類用於生成偽隨機數。此類的實例是線程安全的。然而，此類的實例在加密上是不安全的。該類提供了各種方法調用來生成不同的隨機數據類型，如float、double、int。

構造函數：

• Random()：創建一個新的隨機數生成器
• 隨機(長種子)：使用單個長種子創建一個新的隨機數生成器

聲明：

public class Random
               extends Object
               implements Serializable

方法：

1. java.util.Random.doubles():返回實際上無限的偽隨機雙精度值流，每個值都在零(包含)和一(不包含)之間
   用法：

   public DoubleStream doubles()
   返回：
   a stream of pseudorandom double values

2. java.util.Random.ints():返回有效無限的偽隨機 int 值流
   用法：

   public IntStream ints()
   Returns:
   a stream of pseudorandom int values

3. java.util.Random.longs():返回實際上無限的偽隨機long值流
   用法：

   public LongStream longs()
   Returns:
   a stream of pseudorandom long values

4. 下一個(整數位)：java.util.Random.next(整數位)生成下一個偽隨機數
   用法：

   protected int next(int bits)
   Parameters:
   bits - random bits
   返回：
   the next pseudo random value from this 
   random number generator's sequence

5. java.util.Random.nextBoolean():返回此隨機數生成器序列中的下一個偽隨機、均勻分布的布爾值
   用法：

   public boolean nextBoolean()
   Returns:
   the next pseudorandom, uniformly distributed boolean value 
   from this random number generator's sequence

6. java.util.Random.nextBytes(byte[] 字節):生成隨機字節並將它們放入用戶提供的字節數組中
   用法：

   public void nextBytes(byte[] bytes)
   Parameters:
   bytes - the byte array to fill with random bytes
   Throws:
   NullPointerException - if the byte array is null

7. java.util.Random.nextDouble():返回此隨機數生成器序列中的下一個偽隨機、均勻分布的 0.0 到 1.0 之間的雙精度值
   用法：

   public double nextDouble()
   Returns:
   the next pseudo random, uniformly distributed double 
   value between 0.0 and 1.0 from this 
   random number generator's sequence

8. java.util.Random.nextFloat():返回此隨機數生成器序列中的下一個偽隨機、均勻分布的浮點值(介於 0.0 和 1.0 之間)
   用法：

   public float nextFloat()
   Returns:
   the next pseudorandom, uniformly distributed float value 
   between 0.0 and 1.0 from this 
   random number generator's sequence

9. java.util.Random.nextGaussian():返回此隨機數生成器序列中的下一個偽隨機、高斯 (“normally”) 分布雙精度值，平均值為 0.0，標準差為 1.0
   用法：

   public double nextGaussian()
   Returns:
   the next pseudorandom, Gaussian ("normally") distributed double
   value with mean 0.0 and standard deviation 1.0 from this 
   random number generator's sequence

10. java.util.Random.nextInt()：返回此隨機數生成器序列中的下一個偽隨機、均勻分布的 int 值
    用法：

    public int nextInt()
    Returns:
    the next pseudorandom, uniformly distributed int value from 
    this random number generator's sequence

11. java.util.Random.nextInt(int綁定)：返回從該隨機數生成器的序列中提取的介於 0(含)和指定值(不含)之間的偽隨機、均勻分布的 int 值
    用法：

    public int nextInt(int bound)
    Parameters:
    bound - the upper bound (exclusive). Must be positive.
    返回：
    the next pseudorandom, uniformly distributed int value 
    between zero (inclusive) and bound 
    (exclusive) from this random number generator's sequence
    Throws:
    IllegalArgumentException - if bound is not positive

12. java.util.Random.nextLong():返回此隨機數生成器序列中的下一個偽隨機、均勻分布的long值
    用法：

    public long nextLong()
    Returns:
    the next pseudorandom, uniformly distributed long value
    from this random number 
    generator's sequence

13. java.util.Random.setSeed(長種子):使用單個長種子設置此隨機數生成器的種子
    用法：

    public void setSeed(long seed)
    Parameters:
    seed - the initial seed

Methods inherited from class java.lang.Object

• clone
• equals
• finalize
• getClass
• hashCode
• notify
• notifyAll
• toString
• wait

Java program to demonstrate usage of Random class

// Java program to demonstrate 
// method calls of Random class 
import java.util.Random; 
  
public class Test 
{ 
    public static void main(String[] args) 
    { 
        Random random = new Random(); 
        System.out.println(random.nextInt(10)); 
        System.out.println(random.nextBoolean()); 
        System.out.println(random.nextDouble()); 
        System.out.println(random.nextFloat()); 
        System.out.println(random.nextGaussian()); 
        byte[] bytes = new byte[10]; 
        random.nextBytes(bytes); 
        System.out.printf("["); 
        for(int i = 0; i< bytes.length; i++) 
        { 
            System.out.printf("%d ", bytes[i]); 
        } 
        System.out.printf("]\n"); 
          
          System.out.println(random.nextLong());   
      System.out.println(random.nextInt()); 
       
      long seed = 95; 
      random.setSeed(seed); 
        
      // Note: Running any of the code lines below 
      // will keep the program running as each of the  
      // methods below produce an unlimited random  
      // values of the corresponding type 
  
      /* System.out.println("Sum of all the elements in the IntStream returned = " +  
        random.ints().count()); 
      System.out.println("Count of all the elements in the DoubleStream returned = " +  
        random.doubles().count()); 
      System.out.println("Count of all the elements in the LongStream returned = " +  
        random.longs().count()); 
       
      */
     
  } 
}      

輸出：

4
true
0.19674934340402916
0.7372021
1.4877581394085997
[-44 75 68 89 81 -72 -1 -66 -64 117 ]
158739962004803677
-1344764816

參考：

• Oracle