Java integer to byte array

Going beyond - alternative solutions

Bitwise shifts

Bitwise shifts and masking can achieve the desired transformation:

int yourInt = 123456789; //Replace 123456789 with your desired integer
byte[] byteArr = new byte[4];

for (int i = 0; i < 4; i++) {
    byteArr[i] = (byte) (yourInt >>> (i * 8)); // Magic happens here!
}
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Adjust the shift direction to control endianness.

Guava library

Consider Guava's Ints.toByteArray() for a direct, elegant conversion:

byte[] byteArr = Ints.toByteArray(123456789);
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This method neatly abstracts away conversion complexities.

Arrays.copyOf()

Combine Arrays.copyOf() with range operations for customized byte array management:

int yourInt = 123456789; 
byte[] fullSize = ByteBuffer.allocate(8).putInt(yourInt).array();
byte[] byteArr = Arrays.copyOfRange(fullSize, 4, 8); // Last four bytes are kept
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This approach diversifies array size management and content control.

Deeper insights

Managing byte order (endianness)

Beware of endianness! Specify ByteOrder when working with byte arrays:

int yourInt = 123456789;
ByteBuffer buffer = ByteBuffer.allocate(4);
buffer.order(ByteOrder.LITTLE_ENDIAN); // Use ByteBuffer.order to set endianness
buffer.putInt(yourInt);
byte[] byteArr = buffer.array(); // Now bytes are ordered in little-endian
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Avoiding Integer.toHexString()

Avoid Integer.toHexString() if you need a real byte array. It provides a String representation, not actual byte values.

The BigInteger illusion

Consider using BigInteger for non-primitive types and larger values:

byte[] byteArr = new BigInteger(String.valueOf(123456789)).toByteArray();
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Yet beware - this could introduce padding or sign-related bytes. Interpret with caution.

Traps and tricks

• Underflow and Overflow: Ensure your values fit within the byte's range. Losing data isn't fun!
• Immutable ByteBuffers: You can't modify the byte array from a ByteBuffer once it's retrieved via array().
• Byte Order: Different systems use different endianness. Double-check when writing and reading to avoid headaches.