Java SecureRandom setSeed()方法及示例

setSeed( byte[] seed )

java.security.SecureRandom 类的 setSeed() 方法被用来重新填充这个随机对象。给定的种子是对现有种子的补充，而不是替换。因此，重复调用可以保证永远不会减少随机性。

语法

public void setSeed(byte[] seed)

参数： 该方法将种子作为参数。

注意： 每次Secure Random类都会产生随机输出:

下面是说明setSeed()方法的例子。

例子1 :

// Java program to demonstrate
// setSeed() method
  
import java.security.*;
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
    {
        try {
            // creating the object of SecureRandom
            SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
  
            // Declaring the string variable
            String str = "Tajmahal";
  
            // Declaring the byte Array b
            byte[] b = str.getBytes();
  
            // Reseeding the random object
            sr.setSeed(b);
  
            // getting the seeds
            byte[] seeds = sr.getSeed(10);
  
            // printing the seed serialwise
            for (int i = 0; i < seeds.length; i++)
                System.out.println("Seed[" + i + "] : " + seeds[i]);
        }
  
        catch (NoSuchAlgorithmException e) {
  
            System.out.println("Exception thrown : " + e);
        }
  
        catch (ProviderException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出

Seed[0]:69
Seed[0] : 23
Seed[1] : -99
Seed[2] : -51
Seed[3] : 107
Seed[4] : 41
Seed[5] : -96
Seed[6] : -93
Seed[7] : -86
Seed[8] : 127
Seed[9] : 47

例2 :

// Java program to demonstrate
// setSeed() method
  
import java.security.*;
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
    {
        try {
            // creating the object of SecureRandom
            SecureRandom sr = new SecureRandom(new byte[] { 1, 2, 3, 4 });
  
            // Declaring the string variable
            String str = "Tajmahal";
  
            // Declaring the byte Array b
            byte[] b = str.getBytes();
  
            // Reseeding the random object
            sr.setSeed(b);
  
            // getting the seeds
            byte[] seeds = sr.getSeed(10);
  
            // printing the seed serialwise
            for (int i = 0; i < seeds.length; i++)
                System.out.println("Seed[" + i + "]:" + seeds[i]);
        }
  
        catch (ProviderException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出

Seed[0]:92
Seed[1]:127
Seed[2]:28
Seed[3]:-127
Seed[4]:-100
Seed[5]:-110
Seed[6]:86
Seed[7]:-55
Seed[8]:48
Seed[9]:-78

setSeed(long seed )

java.security.SecureRandom 类的 setSeed(long seed) 方法被用来重新填充这个随机对象，使用给定的long seed中包含的八个字节。给定的种子是对现有种子的补充，而不是替换。因此，重复调用可以保证永远不会减少随机性。

语法

public void setSeed( long seed )

参数： 该方法将 种子 作为参数。

注意： 每次Secure Random类都会产生随机输出:

下面是说明setSeed()方法的例子。

例子1 :

// Java program to demonstrate
// setSeed() method
  
import java.security.*;
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
        try {
            // creating the object of SecureRandom
            SecureRandom sr = SecureRandom.getInstance("SHA1PRNG", "SUN");
  
            // Reseeding the random object
            sr.setSeed(101L);
  
            // getting the seeds
            byte[] seeds = sr.getSeed(10);
  
            // printing the seed serialwise
            for (int i = 0; i < seeds.length; i++)
                System.out.println("Seed[" + i + "] : " + seeds[i]);
        }
  
        catch (NoSuchAlgorithmException e) {
  
            System.out.println("Exception thrown : " + e);
        }
  
        catch (ProviderException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出

Seed[0] : -36
Seed[1] : -65
Seed[2] : -94
Seed[3] : 16
Seed[4] : -104

例2 :

// Java program to demonstrate
// setSeed() method
  
import java.security.*;
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
    {
        try {
            // creating the object of SecureRandom
            SecureRandom sr = new SecureRandom(new byte[] { 1, 2, 3, 4 });
  
            // Reseeding the random object
            sr.setSeed(101L);
  
            // getting the seeds
            byte[] seeds = sr.getSeed(10);
  
            // printing the seed serialwise
            for (int i = 0; i < seeds.length; i++)
                System.out.println("Seed[" + i + "]:" + seeds[i]);
        }
  
        catch (ProviderException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出

Seed[0]:-29
Seed[1]:-93
Seed[2]:6
Seed[3]:66
Seed[4]:126
Seed[5]:93
Seed[6]:-58
Seed[7]:-91
Seed[8]:-62
Seed[9]:-58