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 a possible implementation in working code of the pseudo code solution written by silvertab.

Thanks silvertab!

public class Array {

   public static  T[] concat(T[] a, T[] b, ArrayBuilderI builder) {
      T[] c = builder.build(a.length + b.length);
      System.arraycopy(a, 0, c, 0, a.length);
      System.arraycopy(b, 0, c, a.length, b.length);
      return c;
   }
}

Following next is the builder interface.

Note: A builder is necessary because in java it is not possible to do

new T[size]

due to generic type erasure:

public interface ArrayBuilderI {

   public T[] build(int size);
}

Here a concrete builder implementing the interface, building a Integer array:

public class IntegerArrayBuilder implements ArrayBuilderI {

   @Override
   public Integer[] build(int size) {
      return new Integer[size];
   }
}

And finally the application / test:

@Test
public class ArrayTest {

   public void array_concatenation() {
      Integer a[] = new Integer[]{0,1};
      Integer b[] = new Integer[]{2,3};
      Integer c[] = Array.concat(a, b, new IntegerArrayBuilder());
      assertEquals(4, c.length);
      assertEquals(0, (int)c[0]);
      assertEquals(1, (int)c[1]);
      assertEquals(2, (int)c[2]);
      assertEquals(3, (int)c[3]);
   }
}