Most concise way to insert array of bytes into List<Byte>?

Question

In some code I'm creating a List of Bytes, and want to insert an array of bytes into the list as I am building it. What is the cleanest way of doing this? See code below - thanks.

public class ListInsert {
    public static byte[] getData() {
        return new byte[]{0x01, 0x02, 0x03};
    }

    public static void main(String[] args) {
        final List<Byte> list = new ArrayList<Byte>();
        list.add((byte)0xaa);
        list.add(getData()); // I want to insert an array of bytes into the list here
        list.add((byte)0x55);
    }
}

Good answers below, but I'm intrigued what you're going to do with your list of bytes... — Armand
– Armand, Commented Aug 20, 2010 at 16:29
It's for a device I'm working with, need to send certain message packets out the serial port. — fred basset
– fred basset, Commented Aug 20, 2010 at 19:00
Using a List<Byte> is a really inefficient way to deal with serial coms. You should write your own list-like wrapper around a byte array, or use byte buffers from java.nio. — Cornelius Dol
– Cornelius Dol, Commented Aug 21, 2010 at 3:13

Community · Accepted Answer · 2017-05-23 12:34:25Z

27

IF you have a Byte[] arr -- an array of reference types -- you can use Arrays.asList(arr) to get a List<Byte>.

IF you have a byte[] arr -- an array of primitives -- you can't use Arrays.asList(arr) to get a List<Byte>. Instead you'll get a one-element List<byte[]>.

That is, while a byte can be boxed to a Byte, a byte[] DOES NOT get autoboxed to Byte[]!
_{(also true for other primitives)}

So you have two choices:

Just iterate over each byte in byte[] and add individually
Use libraries
- With Apache Commons Lang, you can convert byte[] to Byte[]
  - You can then Arrays.asList and addAll
- With Guava can convert byte[] immediatelly to List<Byte>

The first option looks like this:

byte[] arr = ...;
for (byte b : arr) {
    list.add(b);
}

The second option with Guava looks like this:

// requires Guava
byte[] arr = ...;
list.addAll(Bytes.asList(arr));

This uses Bytes.asList from package com.google.common.primitives. The package has other conversion utilities for other primitives too. The entire library is highly useful.

With Apache Commons Lang, you can use Byte[] toObject(byte[]) from ArrayUtils:

// requires Apache Commons Lang
byte[] arr = ...;
list.addAll(Arrays.asList(ArrayUtils.toObject(arr)));

1 Comment

fred basset Over a year ago

Thank you, I had not looked at the google primitives package before, will check it out now.

instcode · Accepted Answer · 2010-08-20 16:58:38Z

4

This might not answer your question but it should be a good practice. If you are heavily manipulating an array of bytes, use the ByteBuffer instead. This class have many types of implementation which can give you the best performance & memory usage. One of them is the Direct ByteBuffer which some operations can run natively.

To put a byte or an array of bytes is as simple as eating a candy:

ByteBuffer.put(byte src);
ByteBuffer.put(byte[] src);
ByteBuffer.put(byte[] src, int offset, int length);

And the best thing is when you trying to get the bytes out: directly, no array copy's needed (you need to check the size though) :)

byte[] data = ByteBuffer.array();

Hope you change your mind :)

answered Aug 20, 2010 at 16:58

instcode

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Comments

Colin Hebert · Accepted Answer · 2010-08-20 16:25:02Z

1

There is the Arrays.asList() method which exactly do that:

Arrays.asList(getData());

So in your case :

list.addAll(Arrays.asList(getData()));

answered Aug 20, 2010 at 16:25

Colin Hebert

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2 Comments

polygenelubricants Over a year ago

This doesn't work with byte[]. Arrays.asList doesn't "work" with array of primitives.

Ultimate Gobblement Over a year ago

I thought that autoboxing would handle that, but I guess not for arrays then

Jarekczek · Accepted Answer · 2017-06-25 08:23:49Z

1

Do you really need List<Byte>? I also thought so, but changed my mind. ByteArrayOutputStream was much better for me.

import java.io.ByteArrayOutputStream;
ByteArrayOutputStream bo = new ByteArrayOutputStream();
// fill in buf or get a single byte b
bo.write(buf, 0, bytesRead);
bo.write(b);
byte[] resultArray = bo.toByteArray();

answered Jun 25, 2017 at 8:23

Jarekczek

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