public String[] concat(String[] a, String[] b) {
        int aLen = a.length;
        int bLen = b.length;
        String[] c= new String[aLen+bLen];
        System.arraycopy(a, 0, c, 0, aLen);
        System.arraycopy(b, 0, c, aLen, bLen);
        return c;
    }