Combining three int arrays into one, Java

Question

I'm trying to write a merge method that takes three arrays and moves them into one. I'm quite new to java and the website where I'm submitting this code isn't very helpful with pointing out my error

static int[] mergeArrays(int[] a1, int[] a2, int[] a3) {

int[] answer = new int[a1.length + a2.length + a3.length];
int i,j,k;
for (i = 0; i < a1.length; i++)
    answer[i] = a1[i];

for (j = 0; j < a2.length; j++)
    answer[i++] = a2[j];

for (k = 0; k < a3.length; k++)
    answer[i++] = a3[k];

return answer;
}

Does it give you *any* indication as to what the problem is? As far as I can see that works (provided you don't need to handle null arguments, which doesn't really make sense anyway). — Andy Turner, Jul 04 '16 at 07:54
It doesn't, however this brings up nearly 30 errors at runtime in an unviewable/unaccessable main method. — David Kane, Jul 04 '16 at 08:00
The main method is already completed and I'm unable to see it... not very useful. I'm going to rewrite this and try to sort the arrays, so my result looks like {a1[0], a1[1], a1[2] a2[0 ....... etc] — David Kane, Jul 04 '16 at 08:03
You could specify the platform you are submitting to and the output you are getting. It could be useful. — Danail Alexiev, Jul 04 '16 at 08:06
Finally got it, had an extra } bracket at the end and didn't even notice — David Kane, Jul 04 '16 at 08:13

score 2 · Answer 1 · edited Dec 16 '21 at 09:06

I do not see any benefit in writing a method that merges exactly three arrays. Please consider this more flexible signature:

public static int[] merge(int[]... intArrays);

Also low level loops and index manipulation should be avoided, Java 8 comes to help!

public static int[] merge(int[]... intArrays) {
    return Arrays.stream(intArrays)
            .flatMapToInt(i -> Arrays.stream(i))
            .toArray();
}

This is very concise, has no code duplication, no low level code and can even to be done in a parallel stream if arrays are large or many.

score 0 · Answer 2 · answered Jul 04 '16 at 08:14

0

List<Integer> mergedArray = Arrays.asList(array1); //will give you first list.

mergedArray.addAll(Arrays.asList(array2));
mergedArray.addAll(Arrays.asList(array3));

answered Jul 04 '16 at 08:14

Rohith K

1,433
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1

This won't work since `Arrays.asList()` method returns a fixed-size list. So `.addAll()` method will throw an Exception – tfosra Jul 04 '16 at 08:19
1

You can take a look at this [post](http://stackoverflow.com/questions/16748030/difference-between-arrays-aslistarray-vs-new-arraylistintegerarrays-aslist) – tfosra Jul 04 '16 at 08:21

Combining three int arrays into one, Java

2 Answers2