Question

I have a LinkedHashMap where CommonEnum represents a type of byte[] that I want to keep track of.

LinkedHashMap<CommonEnum, byte[]> map = new LinkedHashMap<CommonEnum, byte[]>();

What is the most efficient way in Java to flatten this into a continuous

byte[]

with the same ordering (thats why the HashMap is Linked).

Answer 1

If you can use a LinkedHashMap<CommonEnum, byte[]>, it gets easier, and I have no idea why you would use Byte[], so I assume this.

I’m not sure about most efficient, but these two would be what I think about:

• 1. create a byte[] large enough (either estimate it or calculate by adding the sizes)
  2. loop through the values, using System.arraycopy for each.
  3. If the array was to long, use Arrays.copyOf to shorten it.
• 1. Create a ByteArrayOutputStream
  2. loop through the values, write each byte[] to the stream.
  3. get the array.

By the way, if your CommonEnum values are always of the same order (and you can use this order as the order in the enum definition), you can use an EnumMap instead.