Any suggestions to simplify / improve this implementation of quicksort?

IntList.java

    public static int[] concatArrays(int[] a1, int[] a2) {
        int n1 = a1.length;
        int n2 = a2.length;
        if(n1 == 0) return a2;
        if(n2 == 0) return a1;

        int n = n1 + n2;
        int counter = 0;
        int[] result = new int[n];
        for(; counter < n1; counter++) {
            result[counter] = a1[counter];
        }
        for(; counter < n; counter++) {
            result[counter] = a2[counter - n1];
        }
        return result;
    }

    public static int[] concatArrays(int[] a1, int a2) {
        int[] a2New = new int[] {a2};
        return concatArrays(a1, a2New);
    }



    public static int[] sort(int[] data) {
        if(data.length == 0) return new int[0];
        int nBefore = 0;
        int nAfter = 0;
        int[] beforeArray = new int[data.length];
        int[] afterArray  = new int[data.length];
        for(int i = 1; i < data.length; i++) {
            if(data[i] < data[0]) {
                beforeArray[nBefore++] = data[i];
            }
            else {
                afterArray[nAfter++] = data[i];
            }
        }
        int[] beforeArrayTrimmed = new int[nBefore];
        int[] afterArrayTrimmed = new int[nAfter];
        System.arraycopy(beforeArray, 0, beforeArrayTrimmed, 0, nBefore);
        System.arraycopy(afterArray, 0, afterArrayTrimmed, 0, nAfter);
        return concatArrays(
                concatArrays(sort(beforeArrayTrimmed), data[0]),
                sort(afterArrayTrimmed)
        );
    }