Basic Java Array and For Loop

Question

I am taking a Java class and have read the same explanation over and over and I just want to make sure I am understanding it correctly.

The example in the class they provide is a dice rolling game and they want to see the frequency of rolls per number.

The code snippet that I am uncertain on is this:

for(int roll = 1; roll < 1000; roll++){
    ++freq[1+rand.nextInt(6)];
}

I understand this part: 1+rand.nextInt(6)

But I don't understand this part: ++freq and how it tallys the results

I am understanding this as (with the example I rolled a 4):

for(int roll = 1; roll < 1000; roll++){
    ++freq[4];
    //all indexes in freq are == 0 to start
    //freq[4] is index 4 in the array. It was 0 but is now == to 1
    //freq[0], freq[1], freq[2], freq[3], freq[5], and freq[6] are all still == to 0
}

for(int roll = 1; roll < 1000; roll++){
    ++freq[6];
    //freq[6] is index 6 in the array. It was 0 but is now == to 1
    //freq[0], freq[1], freq[2], freq[3], and freq[5] are all still == to 0
    //freq[4] and freq[6] are both == to 1
}

Is this correct?

For the record, ++freq[1+rand.nextInt(6)]; is rather unclear code. Unless you are developing on a 2 inch screen or are penalised for writing more lines of code, it is much clearer to write it as a variable int roll = 1 + rand.nextInt(6); and an increment ++freq[roll];. — Andy Turner
– Andy Turner, Commented Aug 25, 2018 at 15:31

pahan · Accepted Answer · 2018-08-25 15:42:01Z

3

int[] freq = new int[7];

    for(int roll = 1; roll < 1000; roll++){
        ++freq[1+rand.nextInt(6)];
    }

In the above code rand.nextInt(6) returns a value from 0 to 5 which is used to access the relevant integer value of the array freq

++freq part increases the accessed integer value by 1.

Example: if rand.nextInt(6) returns 2,

freq[1 + 2] = freq[1 + 2] + 1;

However, from 1 + rand.nextInt(6), 0 is never produced. Therefore, the first element of freq array should be ignored.

freq[n] will give you the frequency of the nth face.

answered Aug 25, 2018 at 15:42

pahan

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1 Comment

Olivia Over a year ago

this was a super helpful breakdown. Thank you!!

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