CODEWITHSUNDEEP
javaarrayslistbyte
mysomic
mysomic

Reputation: 1567

Creating a byte[] from a List<Byte>

What is the most efficient way to do this?

Upvotes: 9

Views: 12952

Answers (3)

Bombe
Bombe

Reputation: 83846

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. However, none of those ways gets around a) creating an array and b) assigning each element. This one uses an iterator.

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

Upvotes: 16

finnw
finnw

Reputation: 48619

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();

Upvotes: 2

unwind
unwind

Reputation: 399753

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.

Upvotes: 4

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