Question

I need to convert a byte[] of size 4 to type long for my Android app. I found a function byteArrayToLong(byte_array) which is in the java.io.Bits package, but it isn’t working in my application.

Are there any other alternative functions?

Answer 1

Use java.nio.ByteBuffer:

byte[] data = new byte[] {50, -106, 40, -22};
ByteBuffer buffer = ByteBuffer.wrap(data);
System.out.println(buffer.getLong());

Edit

Of course, @Kaito is right: you need an array of 8 bytes instead. Also, as others mentioned, you may choose an order in which your bytes will be read (BIG_ENDIAN by default):

    byte[] data = new byte[] {50, -106, 40, -22, 0, 0, 0, 0};
    ByteBuffer buffer = ByteBuffer.wrap(data);
    buffer.order(ByteOrder.BIG_ENDIAN);
    System.out.println(buffer.getLong()); // 3645145933890453504
    buffer = ByteBuffer.wrap(data);
    buffer.order(ByteOrder.LITTLE_ENDIAN);
    System.out.println(buffer.getLong()); // 3928528434

Also, why to prefer an API method? For the sake of simplicity: instead of recognizing byte to long conversion in bitwise shifts you can read what happens here in plain English.