Merge 3 list items

Question

I have 3 list in Java and how do I merge them?

list1 = [10,20,30]
list2 = [40,50,60]
list3 = [70]

Output

res = [10,40,70,20,50,30,60]

I'm familiar with writing a achieving the result but would like to know if there is any libraries that I can use it.

"I'm familiar with...", can you give us an example of what you normally do? — Jon Egeland, Feb 12 '15 at 21:40

score 1 · Answer 1 · edited May 23 '17 at 11:43

1

res = ArrayUtils.addAll(list1, list2);
res = ArrayUtils.addall(res,list3);

Also, see many more options on how to do this here.

edited May 23 '17 at 11:43

Community

1
1

answered Feb 12 '15 at 21:41

barq

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score 0 · Answer 2 · edited May 23 '17 at 12:27

from How to mix two arrays in Java?

int[] merge(int[]... arrays) {
    int length = 0;
    for (int[] a: arrays) {
        length += a.length;
    }
    int result[] = new int[length];
    for (int i = 0, j = 0; j < length; ++i) {
        for (int[] a: arrays) {
            if (i < a.length) {
                result[j++] = a[i];
            }
        }
    }
    return result;
}

then simply

merge(list1, list2, list3)

score 0 · Answer 3 · answered Feb 13 '15 at 04:37

You can use the normal Java 7 libraries:

List result = new ArrayList();
result.addAll(list1); result.addAll(list2); result.addAll(list3);`

or shorter:

List result = new ArrayList();
Collections.addAll(result, list1, list2, list3);

I guess there is also a Java 8 stream solution.

Merge 3 list items

3 Answers3