Combine two arrays into one

Question

I am trying to combine two arrays into one big array. But I don't understand why it wont work.

Here's my code:

     public class TestaCombine {

private int[] arrayX = new int[20];
private int[] arrayY = new int[6];

private int[] ratings;


public void getRanks(){

    arrayX[0] = 3;
    arrayX[1] = 4;
    arrayX[2] = 2;
    arrayX[3] = 6;
    arrayX[4] = 2;
    arrayX[5] = 5;

    arrayY[0] = 9;
    arrayY[1] = 7;
    arrayY[2] = 5;
    arrayY[3] = 10;
    arrayY[4] = 6;
    arrayY[5] = 8;

}


public void combine(){

    ratings = new int[arrayX.length + arrayY.length];
    System.arraycopy(arrayX, 0, ratings, 0,  arrayX.length);
    System.arraycopy(arrayY, 0, ratings, arrayX.length, arrayY.length);

    Arrays.sort(ratings);

}


public void print(){

    System.out.println(Arrays.toString(ratings));

}

public static void main(String[] args){

    TestaCombine tc = new TestaCombine();

    tc.getRanks();
    tc.combine();
    tc.print();

}

The output I am getting looks like this: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 3, 4, 5, 5, 6, 6, 7, 8, 9, 10]

Don't understand where all the 0s comes from.

Did you mean to create `arrayX` as a `new int[6]` instead of `new int[20]`? You only initialized 6 of 20 values in it. — user2357112, Apr 02 '14 at 09:51
possible duplicate of [How to concatenate two arrays in Java?](http://stackoverflow.com/questions/80476/how-to-concatenate-two-arrays-in-java) — gpgekko, Apr 02 '14 at 09:53
when you do int[] arrayX = new int[20], it will allocate your array with 0s. both arrayX and arrayY will have 0s in them. I haven't looked a way of fixing your problem yet. — Andrei Sfat, Apr 02 '14 at 09:55
what would be your expected results after the combine for your `ratings` array? is this correct? `[2, 2, 3, 4, 5, 5, 6, 6, 7, 8, 9, 10] ` — Andrei Sfat, Apr 02 '14 at 09:58

score 3 · Accepted Answer · answered Apr 02 '14 at 09:53

Note that the size of arrayX is 20. By default, ints have 0 value in Java. See the JLS - 4.12.5. Initial Values of Variables:

For type int, the default value is zero, that is, 0.

So when you do:

System.arraycopy(arrayX, 0, ratings, 0,  arrayX.length);

It copies the zeros as well.

Taks · Answer 2 · 2014-04-02T09:57:57.880

It is because you have created one array with size of 20 and you only initialized 6 values within it, the rest of values where initialized during array initialization and they were all populated to 0's. When you combined array of size 20 and array of size 6 you received array of size 26 where 14 values are 0's

I would also like to recommend you apache commons libraries which contains nice set of tools for managing different collections.

score 0 · Answer 3 · answered Apr 02 '14 at 09:54

You're combining an array of size 6 with an array of size 20. The resulting array therefore has a size of 26.

But you've only specified 12 values, so the rest are filled in with values of 0. As you're sorting the collections, this also puts all the 0s at the start of the array.

Combine two arrays into one

3 Answers3