How to concatenate two-dimensional arrays in Java

Question

I have a situation where I need to concatenate two two-dimensional arrays.

Object[][] getMergedResults() {
    Object[][] a1 = getDataFromSource1();
    Object[][] a2 = getDataFromSource2();
    // I can guarantee that the second dimension of a1 and a2 are the same
    // as I have some control over the two getDataFromSourceX() methods

    // concat the two arrays
    List<Object[]> result = new ArrayList<Object[]>();
    for(Object[] entry: a1) {
        result.add(entry);
    }
    for(Object[] entry: a2) {
        result.add(entry);
    }
    Object[][] resultType = {};

    return result.toArray(resultType);
}

I have looked at the solutions for the concatenation of 1-dimensional arrays in this post but have been unable to make it work for my two-dimensional arrays.

So far, the solution I have come up with is to iterate over both arrays and adding each member to a ArrayList and then returning toArray() of that array list. I'm sure there must be an easier solution, but have so far been unable to come with one.

Solution 1

You could try

Object[][] result = new Object[a1.length + a2.length][];

System.arraycopy(a1, 0, result, 0, a1.length);
System.arraycopy(a2, 0, result, a1.length, a2.length);

Solution 2

You could use Apache Commons Library - ArrayUtils. Change only the index for second dimension and merge the whole lines.