Combine two integer arrays [duplicate]

Answer 1

You can't add them directly, you have to make a new array and then copy each of the arrays into the new one. System.arraycopy is a method you can use to perform this copy.

int[] array1and2 = new int[array1.length + array2.length];
System.arraycopy(array1, 0, array1and2, 0, array1.length);
System.arraycopy(array2, 0, array1and2, array1.length, array2.length);

This will work regardless of the size of array1 and array2.

Answer 2

int [] newArray = new int[old1.length+old2.length];
System.arraycopy( old1, 0, newArray, 0, old1.length);
System.arraycopy( old2, 0, newArray, old1.length, old2.length );

Don't use element-by-element copying, it's very slow compared to System.arraycopy()

Answer 3

I think you have to allocate a new array and put the values into the new array. For example:

int[] array1and2 = new int[array1.length + array2.length];
int currentPosition = 0;

for( int i = 0; i < array1.length; i++) {
    array1and2[currentPosition] = array1[i];
    currentPosition++;
}

for( int j = 0; j < array2.length; j++) {
    array1and2[currentPosition] = array2[j];
    currentPosition++;
}

As far as I can tell just looking at it, this code should work.

Answer 4

NOTE: didn't test it

int[] concatArray(int[] a, int[] b) {
  int[] c = new int[a.length + b.length];
  int i = 0;
  for (int x : a) { c[i] = x; i ++; }
  for (int x : b) { c[i] = x; i ++; }
  return c;
}

Answer 5

Yes but it is not quite that easy. Create a third array that is the size of the two arrays combined and loop through each original array and move the items over. Also look into System.arraycopy().

Answer 6

Here a simple function that use variable arguments:

final static
public int[] merge(final int[] ...arrays ) {
    int size = 0;
    for ( int[] a: arrays )
        size += a.length;

        int[] res = new int[size];

        int destPos = 0;
        for ( int i = 0; i < arrays.length; i++ ) {
            if ( i > 0 ) destPos += arrays[i-1].length;
            int length = arrays[i].length;
            System.arraycopy(arrays[i], 0, res, destPos, length);
        }

        return res;
}

To use:

int[] array1 = {1,2,3};
int[] array2 = {4,5,6};
int[] array3 = {7,8,9};
int[] array1and2and3 = merge(array1, array2, array3);
for ( int x: array1and2and3 ) 
    System.out.print( String.format("%3d", x) );