Creating a byte[] from a List<Byte>

Question

What is the most efficient way to do this?

Answer 1

The toArray() method sounds like a good choice.

Update: Although, as folks have kindly pointed out, this works with "boxed" values. So a plain for-loop looks like a very good choice, too.

Answer 2

byte[] byteArray = new byte[byteList.size()];
for (int index = 0; index < byteList.size(); index++) {
    byteArray[index] = byteList.get(index);
}

You may not like it but that’s about the only way to create a Genuine™ Array® of byte.

As pointed out in the comments, there are other ways. This one uses an iterator.

byte[] byteArray = new byte[byteList.size()];
int index = 0;
for (byte b : byteList) {
    byteArray[index++] = b;
}

Answer 3

Using Bytes.toArray(Collection<Byte>) (from Google's Guava library.)

Example:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import com.google.common.primitives.Bytes;

class Test {
    public static void main(String[] args) {
        List<Byte> byteList = new ArrayList<Byte>();
        byteList.add((byte) 1);
        byteList.add((byte) 2);
        byteList.add((byte) 3);
        byte[] byteArray = Bytes.toArray(byteList);
        System.out.println(Arrays.toString(byteArray));
    }
}

Or similarly, using PCJ:

import bak.pcj.Adapter;

// ...

byte[] byteArray = Adapter.asBytes(byteList).toArray();