Array as Counters in Java, can anyone help me understand the program below.

Question

class RollaDice{
public static void main (String[] args){
Random Rand = new Random();
it freq[] = new int[7];

for (int roll=1;roll<100;roll++){
++freq[1+rand.nextInt(6);
}
System.out.println("Face\tFrequency");
for (int face=1;face<freq.length;face++){
System.out.println(face+"\t"+freq[face]);
}
}
}

RollaDice will roll between 1-6 and the above program displays the number of times an index is visited with a particular value in it. The value randomly generated between 1 to 6 using the utility called Random.

That is the theoretical part but I am finding it hard to understand the actual logic.
Any one with the explanation ?
I have been following the Buckys java tutorial and if you want more info on this, take a look
https://www.youtube.com/watch?v=pHxtKDENDdE&list=PL484D73FA74A11AC9&index=30

Answer 1

You have a few syntax errors here 😜.

But I assume what you're stuck on is this:

++freq[1+rand.nextInt(6)];

For the sake of simplifying this, allow me to do this:

int randIndex = 1 + rand.nextInt(6);
++freq[randIndex];

Hopefully now it's easier to see.

Initially you created the array:
int freq = new int[7];

new int[7]; Will create an array of size 7, all elements having their default values.
So, it looks like this:

{0,0,0,0,0,0,0}

Now when we do:

int randIndex = 1 + rand.nextInt(6);

This will get a random number from 0-5
Then add it by 1.

So, a random number from 1-6.

*****************
*Note* Normally I Do NOT recommend using '6', use a variable or the length of the array instead. This improves the flexibility and readability of your program. (Flexibility since you can easily change things, readability since I know why you wrote '6').

Like so:

int randIndex = 1 + rand.nextInt(freq.length()-1);

However in this case I suppose it's ok since dice always have 6 sides.
Although, you could do something like this:

final int DICE_SIDES = 6;
and use that local constant instead.
**********************

Anyway..
So we now know it gets a random number.

But what the heck is ++freq[randIndex]; ??

Well, remember from the java course ++x will increment the value by 1.
x in this case is the element in the array.
So, we are incrementing an element at a random index in the array by 1!!