Can you explain me this Java code ?

Question

import java.util.Random;

class Array_Elements {
	public static void main(String arg[]){
		Random rand = new Random();
		int freq[]= new int[7];

for (int roll = 1;roll<=1000;roll++){
			++freq[1+rand.nextInt(6)];
		}
		
		System.out.println("Face&#92;tFrequency");
		
		for (int face=1;face<freq.length;face++){
			System.out.println(face+"&#92;t"+freq[face]);
		}
		
	}
}

I know that it's a program like a dice, Dice is rolled 1000 times and 
it will tell us how many times a number is rolled between 1 to 6 obviously (like a dice)

I just don't get how it does that. I get almost every part of this code
I just don't understand this line ( ++freq[1+rand.nextInt(6)]; ) 
What does it do ?

Can you please explain it from the scratch (That line).

Thank you in advance.

John · Answer

rand.nextInt(6) = generates a random number between 0 and 5
1 + ... = as there is no dice number is zero (0) then add 1 to the proceeding result.
freq[x] = freq[1] ... freq[6] represents the number of the dice, freq[1] means 1
++freq[2] = means adding 1 to the dice number (2) for frequency, actually it is odd, normally presenting freq[2]++ would be easy to understand

If you understand an array is zero based and how to use it, you would never write a code like this and keep adding 1 to the result...

try this...
    Random rnd = new Random();
    int[] freq = new int[6];
    
    // simulates a 6-face dice rolling and its frequency...
    for (int i = 0; i < 1000; i++) {
      int value = rnd.nextInt(6);
      freq[value]++;
    }
    
    // displays the frequency results...
    System.out.println("Face&#92;tFrequency");
    for (int i = 0; i < freq.length; i++) {
      System.out.format("%d&#92;t%d%n", i + 1, freq[i]);
    }

justme · Answer

freq is an array of 7 integers, so whatever random number comes up (1 - 6), that is the integer in the array that gets incremented.

1+rand.nextInt(6) gives a number 1- 6 and this number is used as the index into the freq array.
It would be similar to doing this:
++freq[3]; or ++freq[6]; etc...

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Can you explain me this Java code ?

2 Answers