Append byte after byte array

Question

I have a byte array. But I want array length mod 4=0. So I want to add 00 after array until pass condition. I find many solutions to append array

byte[] arr_combined = new byte[arr_1.length + arr_2.length];
System.arraycopy(arr_1, 0, arr_combined, 0, arr_1.length);
System.arraycopy(arr_2, 0, arr_combined, arr_1.length, arr_2.length);

But I do not want to create new byte array. I only want append byte after a byte array. Thanks

Arrays have a fixed length. if you want to append and change size, use a `List` — Dragondraikk, Jun 11 '15 at 09:22
I would calculate the prefered length, use that result to create a new array, and fill in the data. — Pieter De Bie, Jun 11 '15 at 09:24
As Dragondraikk said, use a List, once you're done convert it to an Array. It will be much easier. — Nyamiou The Galeanthrope, Jun 11 '15 at 09:30

Tagir Valeev · Answer 1 · 2015-06-11T10:31:29.190

As it was already mentioned, Java arrays have fixed size which cannot be changed after array is created. In your case it's probably ok to use ByteArrayOutputStream:

ByteArrayOutputStream out = new ByteArrayOutputStream();
out.write(arr_1);
out.write(arr_2);
byte[] arr_combined = out.toByteArray();

This way you work with primitive byte type (unlike List<Byte>) which will be more efficient. The drawback is that ByteArrayOutputStream is synchronized, so there's some overhead for synchronization (though I guess it's much lower than boxing/unboxing overhead when using List<Byte>). Another drawback is that ByteArrayOutputStream.write is declared to throw IOException. In practice it's never thrown, but you have to catch/rethrow it.

If you don't mind using third-party libraries, there are plenty ways to create convenient wrappers over the primitive types which don't have these drawbacks. For example, TByteArrayList from Trove library.

score 0 · Answer 2 · edited May 23 '17 at 12:32

0

If you have an array you can't modify the length of it. You should use an ArrayList:

List<Byte> bytes = new ArrayList<Byte>();

Here you can add a new element wherever you want just using add method so, supposing that b it's a byte variable:

bytes.add(b);

So, in this way, you can add the number of 00 that you want regardless of the length of the ArrayList.

EDIT: I saw now on this question that you can convert the ArrayList when you have complete it to an array, like this:

Byte[] arrayBytes = bytes.toArray(new Byte[bytes.size()]);

I expect it helps to you!

edited May 23 '17 at 12:32

Community

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answered Jun 11 '15 at 09:31

Francisco Romero

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how can Byte[] be converted to byte[]? – Arthur Eirich Jun 11 '15 at 09:37
@ArthurEirich if you have an array of byte[] called `newBytes` you can do this: `newBytes.toPrimitive(arrayBytes,//Here the value to set if it is null);` – Francisco Romero Jun 11 '15 at 09:44

Append byte after byte array

2 Answers2