How can I concatenate two arrays in Java?

Question

I need to concatenate two String arrays in Java.

void f(String[] first, String[] second) {
    String[] both = ???
}

What is t

Answer 1

Here's my slightly improved version of Joachim Sauer's concatAll. It can work on Java 5 or 6, using Java 6's System.arraycopy if it's available at runtime. This method (IMHO) is perfect for Android, as it work on Android <9 (which doesn't have System.arraycopy) but will use the faster method if possible.

  public static  T[] concatAll(T[] first, T[]... rest) {
    int totalLength = first.length;
    for (T[] array : rest) {
      totalLength += array.length;
    }
    T[] result;
    try {
      Method arraysCopyOf = Arrays.class.getMethod("copyOf", Object[].class, int.class);
      result = (T[]) arraysCopyOf.invoke(null, first, totalLength);
    } catch (Exception e){
      //Java 6 / Android >= 9 way didn't work, so use the "traditional" approach
      result = (T[]) java.lang.reflect.Array.newInstance(first.getClass().getComponentType(), totalLength);
      System.arraycopy(first, 0, result, 0, first.length);
    }
    int offset = first.length;
    for (T[] array : rest) {
      System.arraycopy(array, 0, result, offset, array.length);
      offset += array.length;
    }
    return result;
  }