How to append entire second array to first array in java

Question

I know, We can copy or append elements of array. But, I have around 100 elements in an array. Is there any other way available so I can append array to first array.

Consider I have this two arrays.

 String name1[]={"abc", "def", "ghi"};
 String name2[]={"jkl", "mno", "pqr"};

I want to append name2 array at the end of name1.

Please help me.

would be grateful for help.

• de3: stackoverflow.com/questions/2728476/… stackoverflow.com/questions/80476/…

Answer 1

Guava provides Arrays.concat(T[], T[], Class<T>).

The reason for the Class parameter, FYI, is because generic arrays have a distinct tendency to get upcast. If you did Arrays.concat(Integer[], Long[]), did you want an Object[] back? Or a Number[]? Guava makes you specify so there's no ambiguity...and because all of the alternatives can lead to unpredictable ClassCastExceptions at runtime.

(Disclosure: I contribute to Guava.)

• Renato: Good point about upcasting... The implementation I wrote as an answer here will break only at runtime if you provide an Integer and a Long array...
• Louis Wasserman: Yes, that's correct; it will break. (Conversely, Apache's ArrayUtils will just give you an Object[], which you might be able to cast with an unsafe warning, but that is unsafe: it might lead to unpredictable ClassCastExceptions later.)
• Renato: Added a warning in my answer. Thanks for clarifying.

Answer 2

You will have to create a new array.

An easy implementation using generics and not using any external library:

public static void main(String[] args) {
 String [] a1 = { "a", "b" };
 String [] a2 = { "c", "d", "e", "f" };
 System.out.println(Arrays.toString(append(a1, a2)));
}
public <K> K[] append(K[] a1, K[] a2) {
 K[] a1a2 = Arrays.copyOf(a1, a1.length + a2.length);
 for (int i = a1.length; i < a1a2.length; i++) {
 a1a2[i] = a2[i - a1.length];
 }
 return a1a2;
}

OBS: As Louis Wasserman comments in his answer, Java will upcast the arrays, which can be a problem. For example, if you provide a Long[] and an Integer[] to the append method above, it will compile but you will get a java.lang.ArrayStoreException at run-time!!

Answer 3

You will have to create a new array. Because the length of arrays is fixed.

 String[] list = new String[name1.length+name2.length]

You could loop around the two arrays and add each element to the new array

You could also use apache commons lang library

 String[] both = ArrayUtils.addAll(first, second);

• Vicky: I just checked, but ArrayUtils returns Object[] not String array...Please correct me, If I am going wrong.
• tgoossens: I might be wrong. But arrays can be casted. (Just be careful with this)
• Louis Wasserman: Be very careful with the casted array -- it won't behave quite like a normal String[].