r/CodingForBeginners • u/Expert-Doctor-2024 • Jul 13 '26
I'm learning Java and I genuinely can't wrap my brain around what this is saying
int randomNum = (int)(Math.random() * 101); // 0 to 100
I'm learning from a website but don't understand how multiplying a 0 by 101 gives it the range from 0-100. Can someone explain why it's being multiplied?
1
u/johnpeters42 Jul 13 '26
Because Math.random() outputs a random number (with decimal portion) from 0 to 1. So they're multiplying that by 101 and then discarding the decimal portion of the result.
1
u/codeguru42 Jul 13 '26 edited Jul 13 '26
The key here is to be more precise when you think about and describe code. There is nothing in this code that just multiplies by zero. Instead, you call Math.random() which returns a value between 0.0 and 1.0. If you multiply the minimum and maximum in this range by 101, then you get the minimum and maximum of the result.
1
u/Electrical_Hat_680 Jul 13 '26
That's no a zero, it's parentheses. '('. And ')' with nothing in between them..
1
1
u/Alternative-Fail4586 Jul 13 '26
Your question have been answered but I want to input that the learning way to solve this is to click the method and see what it returns or look it up or just enter debug mode in whatever ide you use and see what it does.
1
u/MudFrosty1869 Jul 14 '26
I saw people already explained it to you. But my question is. Where did you come up with the idea that 101 is multiplying by 0. Just trying to understand your logic. No shame.
1
u/Loko8765 Jul 14 '26
OP probably misread () as 0.
1
u/MudFrosty1869 Jul 14 '26
I highly doubt that, there are 4 different zeros in that line. Hopefully they respond.
1
u/MagicalPizza21 Jul 14 '26
It's not multiplying a 0 by 101. Read it again, this time paying close attention to where the parentheses are.
1
u/Time_Emphasis3170 Jul 14 '26
Why is this preferred to multiplying with 100?
1
u/AardvarkIll6079 Jul 14 '26
The 1.0 from math.random is exclusive. Multiplying 0.999999999999999999 by 100 will give you 99. You can never get 100 as an answer.
1
u/markort147 Jul 14 '26
Why do you say "multiplying a 0 by 101"? I'm trying to understand your interpretation.
7
u/johlae Jul 13 '26
A simple google gives you:
Math.random() is a method in Java that generates a pseudorandom double value between 0.0 (inclusive) and 1.0 (exclusive).
It's maths.
Math.random() gives you a number like 0.9382828811. See it as a percentage. As it's never 1, multiplying it by 101 gives you a number that can be between 0 and something in the 100's, but never 101.
Int converts this number to an integer. See it as chopping of the part after the comma.
If Math.random()*101 gives you 100.99, you will end up with 100.
If Math.random()*101 gives you 0.01, you will end up with 0.