Let's summarize JavaScript, PHP, Java random functions

This time, I will summarize the random function for each language. The reason why it is a random function is that it is often used when creating mini games, and it is one of my favorite functions. There are subtle differences in each language, so I will write an article as a memorandum.

By the way, since the random function also has an algorithm, it is * "pseudo-random number" *, Note that it is not a * "true random number" *.

JavaScript Math.random ()

The JavaScript Math.random () function returns a value greater than or equal to 0 and less than 1.

• 0 is included but 1 is not included!

let num = Math.floor(Math.random() * n) + m;
// n =upper limit, m =lower limit

Math.random () returns in floating point, so use Math.floor () to truncate after the decimal point. "N" sets the upper limit, and "m" sets the lower limit.

Example) Generate random numbers from 1 to 10.

let num = Math.floor(Math.random() * 10) + 1;

1. Math.random () generates random numbers between 0 and 1
2. Multiply by 10 to get a random number of 0 or more and less than 10
3. Truncate after the decimal point by Math.floor () (here it is an integer from 0 to 9)
4. Add 1 to generate an integer from 1 to 10.

The point to note is that it produces numbers less than one.

PHP random_int ()

Use the random_int () function to generate pseudo-random numbers in PHP.

$num = random_int(int $min, int $max);

Pass the lower limit in the first argument and the upper limit in the second argument. Returns a random number containing min to max as an integer value.

Example) Generate random numbers from 1 to 10.

$num = random_int(1, 10);

It's easy because it includes the specified number.

Java Random () class

Java uses the Random () class and nextInt () method found in the java.util package.

int num = new java.util.Random().nextInt(n);

Variables are declared as int type because they are returned as int type. The argument of nextInt () becomes the upper limit value, and a value less than 0 to the upper limit value is returned. Like JavaScript, it does not include the specified upper limit itself!

Example) Generate random numbers from 1 to 10.

public class Main {
 public static void main(String[] args) {
  int num = new java.util.Random().nextInt(10) + 1;
 }
}

Pass the value, noting that it does not include the upper limit.

Summary

Javascript Generate floating point numbers greater than or equal to 0 and less than 1. Learn as a set with Math.floor ().

PHP Lower limit value, upper limit value Returns an integer value including the specified value.

Java Use the Random () class. Pass the upper limit to the argument of the nextInt () method. Returns an integer greater than or equal to 0 and less than the "upper limit".

Spill story

At the training school, I asked the teacher, "Why is it less than 1?" The teacher's answer was

"Why? ..."

I wondered if it was less than 1 for some reason, Only the person who made such a language can understand it. I thought.

Since then, I've stopped questioning predefined functions, variables, and constants.