Java List generics syntax for primitive types

Question

I want to make a growable array of bytes. I.e a list. In c# would usally do the following syntax

List<byte> mylist = new List<byte>();

where as in java this syntax does not work and I have googled around and found the below code

List myList = new ArrayList();

but that is not what I want. Any idea's where I am going wrong?

Answer 1

Use the wrapper class Byte:

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

Then, because of autoboxing, you can still have:

for (byte b : mylist) {

}

Answer 2

You have a Byte class provided by the JRE.

This class is the corresponding class for the byte primitive type.

See here for primitive types.

You can do this :

List<Byte> myList = new ArrayList<Byte>();
byte b = 127;
myList.add(b);
b = 0; // resetting
b = myList.get(0); // => b = 127 again

As Michael pointed in the comments :

List<Byte> myList = new ArrayList<Byte>();
Byte b = null;
myList.add(b);
byte primitiveByte = myList.get(0);

results in :

Exception in thread "main" java.lang.NullPointerException
    at TestPrimitive.main(TestPrimitive.java:12)

Answer 3

Note that using an ArrayList<Byte> to store a growable array of bytes is probably not a good idea, since each byte gets boxed, which means a new Byte object is allocated. So the total memory cost per byte is one pointer in the ArrayList + one Byte object.

It's probably better to use a java.io.ByteArrayOutputStream. There, the memory cost per byte is 1 byte.

We can provide better advice if you describe the context a little more.

Answer 4

You could also use TByteArrayList from the GNU Trove library.