Java.util.Random class in Java

Last Updated : 07 May, 2019

Random class is used to generate pseudo-random numbers in java. An instance of this class is thread-safe. The instance of this class is however cryptographically insecure. This class provides various method calls to generate different random data types such as float, double, int.

Constructors:

Random(): Creates a new random number generator
Random(long seed): Creates a new random number generator using a single long seed

Declaration:

public class Random
               extends Object
               implements Serializable

Methods:

java.util.Random.doubles(): Returns an effectively unlimited stream of pseudo random double values, each between zero (inclusive) and one (exclusive)
Syntax:
```
public DoubleStream doubles()
Returns:
a stream of pseudorandom double values
```
java.util.Random.ints(): Returns an effectively unlimited stream of pseudo random int values
Syntax:
```
public IntStream ints()
Returns:
a stream of pseudorandom int values
```
java.util.Random.longs(): Returns an effectively unlimited stream of pseudo random long values
Syntax:
```
public LongStream longs()
Returns:
a stream of pseudorandom long values
```

next(int bits): java.util.Random.next(int bits) Generates the next pseudo random number
Syntax:

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

java.util.Random.nextBoolean(): Returns the next pseudo random, uniformly distributed boolean value from this random number generator’s sequence
Syntax:
```
public boolean nextBoolean()
Returns:
the next pseudorandom, uniformly distributed boolean value 
from this random number generator's sequence
```

java.util.Random.nextBytes(byte[] bytes) :Generates random bytes and places them into a user-supplied byte array
Syntax:

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

java.util.Random.nextDouble(): Returns the next pseudo random, uniformly distributed double value between 0.0 and 1.0 from this random number generator’s sequence
Syntax:
```
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
```
java.util.Random.nextFloat(): Returns the next pseudo random, uniformly distributed float value between 0.0 and 1.0 from this random number generator’s sequence
Syntax:
```
public float nextFloat()
Returns:
the next pseudorandom, uniformly distributed float value 
between 0.0 and 1.0 from this 
random number generator's sequence
```
java.util.Random.nextGaussian(): Returns the next pseudo random, Gaussian (“normally”) distributed double value with mean 0.0 and standard deviation 1.0 from this random number generator’s sequence
Syntax:
```
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
```
java.util.Random.nextInt(): Returns the next pseudorandom, uniformly distributed int value from this random number generator’s sequence
Syntax:
```
public int nextInt()
Returns:
the next pseudorandom, uniformly distributed int value from 
this random number generator's sequence
```

java.util.Random.nextInt(int bound): Returns a pseudo random, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator’s sequence
Syntax:

public int nextInt(int bound)
Parameters:
bound - the upper bound (exclusive). Must be positive.
Returns:
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

java.util.Random.nextLong(): Returns the next pseudorandom, uniformly distributed long value from this random number generator’s sequence
Syntax:
```
public long nextLong()
Returns:
the next pseudorandom, uniformly distributed long value
from this random number 
generator's sequence
```
java.util.Random.setSeed(long seed): Sets the seed of this random number generator using a single long seed
Syntax:
```
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()); 
       
      */
     
  } 
}      

Output:

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

Reference:

Oracle

Java.lang.Void Class in Java

Mayank Kumar

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Java.util.Random class in Java

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