How to Convert an Integer to a Byte Array in Java?

Convert Integer into Byte Array (Java)

In Java, converting an Integer to a Byte Array can be achieved using various approaches. One efficient method involves employing the ByteBuffer class:

ByteBuffer b = ByteBuffer.allocate(4);
b.putInt(0xAABBCCDD);

byte[] result = b.array();

In the code snippet above, the ByteBuffer's byte order is set to BIG_ENDIAN. As a result, result[0] contains the most significant byte (0xAA), followed by result[1] (0xBB), result[2] (0xCC), and result[3] (0xDD).

Alternatively, you can convert the integer manually:

byte[] toBytes(int i) {
  byte[] result = new byte[4];

  result[0] = (byte) (i >> 24);
  result[1] = (byte) (i >> 16);
  result[2] = (byte) (i >> 8);
  result[3] = (byte) (i);

  return result;
}

The ByteBuffer class provides optimized methods for such tasks. Notably, java.nio.Bits defines helper methods used by ByteBuffer.putInt():

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 are designed to extract individual bytes from an integer efficiently.

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