3D Array with Java (testing example from "Java: The Complete Reference, 9th edition)

Question

I was trying to reproduce a code from the book I am reading and can't get to make it work. Here is the code:

public class ThreeDArray {

public static void main(String[] args) {
    int threeD [][][] = new int [3][4][5];
    int i, j, k;
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 4; j++) {
            for (k = 0; k < 5; k++) {
                threeD [i][j][k] = i*j*k;
            }
        }
        for (i = 0; i < 3; i++) {
            for (j = 0; j < 4; j++) {
                for (k = 0; k < 5; k++) {
                    System.out.print(threeD[i][j][k]+"  ");
                }
                System.out.println("");
            }
            System.out.println("");
        }
    }
}
}

I am getting this output:

0  0  0  0  0  
0  0  0  0  0  
0  0  0  0  0  
0  0  0  0  0  

0  0  0  0  0  
0  0  0  0  0  
0  0  0  0  0  
0  0  0  0  0  

0  0  0  0  0  
0  0  0  0  0  
0  0  0  0  0  
0  0  0  0  0

I am getting all zeros here and I can't find the mistake here. Please advise what is wrong here.

Okay, you've shown us what's not supposed to happen, but haven't told us what's supposed to happen instead. — MattD
– MattD, Commented Jan 20, 2015 at 20:47

Andy Brown · Accepted Answer · 2015-01-20 20:48:25Z

1

Wrong bracket placement: your second for loop should be outside the first:

int i, j, k;
for (i = 0; i < 3; i++) {
    for (j = 0; j < 4; j++) {
        for (k = 0; k < 5; k++) {
            System.out.printf("%d %d %d %d %n", i, j, k, i * j * k);
            threeD [i][j][k] = i*j*k;
        }
    }
} // move to here ...
for (i = 0; i < 3; i++) {
    for (j = 0; j < 4; j++) {
        for (k = 0; k < 5; k++) {
            System.out.print(threeD[i][j][k]+"  ");
        }
        System.out.println("");
    }
    System.out.println("");
}
// ... from here

With the way you had it you were incrementing i with your print loop, which meant your first loop of i exited on the second iteration. Now it prints:

0  0  0  0  0  
0  0  0  0  0  
0  0  0  0  0  
0  0  0  0  0  

0  0  0  0  0  
0  1  2  3  4  
0  2  4  6  8  
0  3  6  9  12  

0  0  0  0  0  
0  2  4  6  8  
0  4  8  12  16  
0  6  12  18  24

answered Jan 20, 2015 at 20:48

Andy Brown

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2 Comments

fthnm2014 Over a year ago

Thanks Andy! I can't believe I missed that.

Andy Brown Over a year ago

@fthnm2014. For what it's worth, I would avoid declaring int for a loop outside the for. Put your bracket in the wrong place again, but remove the int i, j, k declarations and declare your for loops as for (int ...). Your compiler would have probably thrown an error along the lines of Duplicate local variable i that you would have spotted it.

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