How to generate random numbers in java

How to generate random numbers in Java: 1. Use the [java.util.Random] class to generate a random number generator; 2. The returned value is a double value of [[0.0,1.0)].

The operating environment of this tutorial: windows7 system, java10 version, DELL G3 computer. This method is suitable for all brands of computers.

How to generate random numbers in java:

1. The first type

The first type requires the use of the java.util.Random class to generate a Random 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. Take code as an 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);
    　　}
    }

The five numbers generated by my compiler are all 85,88,47,13,54. If Random r = new Random() is used, the random numbers generated will be different. This is determined The result of the seed.

2. The second method

The value returned by the second method is a double value of [0.0,1.0). Since the double type number has high precision, it can be used to a certain extent. Treat it as a random number, and use (int) to perform type conversion to get an integer random number. The code is as follows.

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

3. The third method

Although the third method is not commonly used, it is also an idea. The method returns a long number of milliseconds from 0:00:00 on January 1, 1970 (this is related to UNIX systems) to the present. After taking the modulo, 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);
    
}

Related learning recommendations: java basics

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