Efficient Conversion of Integers to Byte Arrays in Java

Converting an integer to a byte array can be useful for various purposes, such as network transmissions or data storage. There are multiple approaches to achieve this conversion.

ByteBuffer Class:

One efficient method is using the ByteBuffer class. ByteBuffer is a buffer that stores binary data and provides various operations to manipulate it. To convert an integer to a byte array using ByteBuffer:

ByteBuffer b = ByteBuffer.allocate(4); // Allocate a 4-byte buffer
b.putInt(0xAABBCCDD); // Write the integer value to the buffer

byte[] result = b.array(); // Retrieve the byte array from the buffer

Here, the byte order of the buffer ensures that the bytes are arranged in the correct order.

Manual Conversion:

Alternatively, you can manually convert the integer to a byte array:

byte[] toBytes(int i) {
  // Create a new byte array of length 4
  byte[] result = new byte[4];
  
  // Shift bits and assign to each byte
  result[0] = (byte) (i >> 24);
  result[1] = (byte) (i >> 16);
  result[2] = (byte) (i >> 8);
  result[3] = (byte) i;
  
  return result;
}

This approach requires explicit bit-shifting and assignment to each byte.

Helper Methods in java.nio.Bits:

The ByteBuffer class utilizes internal helper methods defined in the java.nio.Bits class:

private static byte int3(int x) { return (byte)(x >> 24); }
private static byte int2(int x) { return (byte)(x >> 16); }
private static byte int1(int x) { return (byte)(x >>  8); }
private static byte int0(int x) { return (byte)(x >>  0); }

These methods simplify the bit-shifting operations mentioned above.