在Java中有效串联2个字节

Question

I am working on a program where I am trying to reduce the amount of memory allocated, I previously use to concatenate strings but the problem was that I do this process several million times and the more I did it the longer it took to allocate these strings. Instead now I am trying work with bytes. I want to do something like this:

byte[] arr = new byte[5];
byte cat = arr[0] + arr[1]  //this addition would give me an error obviously. It's for demostration purposes

System.out.println(cat);

I just want to take the first byte and put the second one right after it without using any form of String Class as it requires more overhead to concatenate strings as such. Is there a way I can do this with minimal operations?

Answer 1

Create a new output byte array of the size equal to the sum of all your bytes that are to concatenated in a new byte array using System.arraycopy()

As System.arraycopy() is native call, it will be certainly faster than String concatenation.

Answer 2

If you want to "concatenate" two or more bytes, into a new byte array, just use the array initializer syntax:

byte a = 1;
byte b = 42;
byte c = 99;

byte[] cat = {a,b,c};

System.out.println(Arrays.toString(cat)); // prints: [1, 42, 99]

Your example is however more akin to a substring() call, and for that you should use Arrays.copyOfRange() , eg

byte[] arr = {5,4,3,2,1};

byte[] cat = Arrays.copyOfRange(arr, 0, 2);

System.out.println(Arrays.toString(cat)); // prints: [5, 4]