How to generate random numbers in java

The generation of random numbers is very commonly used in some codes, and it is also something we must master. There are three main ways to generate random numbers in Java:

The first one: new Random()

You need to use the java.util.Random class to generate a random number Number generator is also the most commonly used one. It has two constructors, Random() and Random(long seed). The first one uses the current time as the default seed, and the second one uses the specified seed value. After generation, different types of numbers are generated with the help of different statements.

The seed is the first value used to generate a random number. The mechanism is to use a function to convert the value of this seed into a certain point in the random number space, and the generated random numbers are evenly distributed in space. The random numbers generated in the future are related to the previous random number.

Example:

public static void main(String[] args)
{    
　　Random r = new Random(1);
　　for(int i=0 ; i<5 ;  i++)
　　{
　　　　int ran1 = r.nextInt(100);
　　　　System.out.println(ran1);
　　}
}

Second type: Math.random()

The value returned by the Math.random() method is [0.0,1.0 ) double type value. Since the double type number has high precision, it can be regarded as a random number to a certain extent. By using (int) to perform type conversion, the integer random number can be obtained. The code is as follows.

public static void main(String[] args)
    {    
      int max=100,min=1;4         
      int ran2 = (int) (Math.random()*(max-min)+min); 
      System.out.println(ran2);6     }

Third type: currentTimeMillis()

The currentTimeMillis() method returns 0:00:00 on January 1, 1970 (this is related to UNIX systems ) to the current long millisecond number, after taking the modulus, a random number within the required range can be obtained.

public static void main(String[] args)
    {    
        int max=100,min=1;
        long randomNum = System.currentTimeMillis();  
        int ran3 = (int) (randomNum%(max-min)+min);  
        System.out.println(ran3);
        
    }

For more java knowledge, please pay attention to the java basic tutorial column.

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