Question

Looking at the output of this particular method is confusing to me. I’m trying to understand exactly what it’s doing.

This is the method:

for (int i = 0; i < 4; i ++) {
    for (int j = 0; j < 9; j++) {
    if (j==5) {
        break;
    }
    if ((j==0) || (i==0)) {
        continue;
    }
    if (!((j*i % 3) != 0)) {
    System.out.println(j*i);
    }
}

}

I know what the output is but I’m still not sure how it’s working, which is why I am asking here. So, This method will go through j until it reaches 5, then it breaks.

Then it increments i, j is 0. J != 5 so it doesn’t break, j == 0 so continue
But then J becomes 3 and I is 1. This is where I’m lost. Where did 3 come from??

I was using this to print out what was going on behind the scenes

    public static void tester() {
    for (int i = 0; i < 4; i ++) {
        for (int j = 0; j < 9; j++) {
            if (j==5) {
                System.out.println("j == 5, breaking");
                break;
            }
            if ((j==0) || (i==0)) {
                System.out.println("J is " + j);
                System.out.println("I is " + i);
                System.out.println("j or i == 0, continuing");
                continue;
            }
            if (!((j*i % 3) != 0)) {
                System.out.println("J is " + j);
                System.out.println("I is " + i);
                System.out.println(j*i);
            }
        }
        System.out.println();
    }
}

And the output is as follows:

J is 0

I is 0

j or i == 0, continuing

J is 1

I is 0

j or i == 0, continuing

J is 2

I is 0

j or i == 0, continuing

J is 3

I is 0

j or i == 0, continuing

J is 4

I is 0

j or i == 0, continuing

j == 5, breaking


J is 0

I is 1

j or i == 0, continuing

J is 3

I is 1

3

j == 5, breaking


J is 0

I is 2

j or i == 0, continuing

J is 3

I is 2

6

j == 5, breaking


J is 0

I is 3


j or i == 0, continuing

J is 1

I is 3

3

J is 2

I is 3

6

J is 3

I is 3

9

J is 4

I is 3

12

j == 5, breaking

Answer 1

The 3 (and later on, the 6), is occurring from this piece of code…

        if (!((j*i % 3) != 0)) {
            System.out.println("J is " + j);
            System.out.println("I is " + i);
            System.out.println(j*i);
        }

Effectively what !((j*i % 3) != 0) is saying is, when j*i/3 has a remainder of 0, it runs the code within this if statement. In other words, it runs this if code whenever j*i is a multiple of 3 (3, 6, 9, 12)

The logic is hard to follow – it’d be better to write it like this…

        if ((j*i % 3) == 0) {
            System.out.println("J is " + j);
            System.out.println("I is " + i);
            System.out.println(j*i);
        }

In the original way, all the ! symbols and multiple brackets/braces make it hard to read.