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In Java, data is stored in big-endian format (also called network order). That is, all data is represented sequentially starting from the most significant bit (MSB) to the least significant. Prior to JDK 1.4, custom methods had to be defined to be compatible with little-endian systems that use the reverse byte order. Handling byte order related issues is critical when data is to be exchanged in a networked environment that consists of machines varying in endianness. Failure to handle such cases data ordering issues can cause misinterpretations and unexpected program behavior.

Noncompliant Code Example

The class java.io.DataInputStream class defines read methods (readByte, readShort, readInt, readLong, readFloat and readDouble) and the corresponding write methods. All these methods work with big-endian data only. The use of these methods can be unsafe while interfacing with traditional languages such as C or C++, that do not provide any guarantees on endianness. This noncompliant code example shows such a discrepancy.

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Assuming that an integer value is to be read from the file, read and write methods can be defined for handling little-endian data. The readLittleEndianInteger() method reads data into a byte buffer and then pieces together the integer in the right order. Long values can be handled by defining a byte buffer of size eight. The writeLittleEndianInteger() method obtains bytes by repeatedly casting the integer so that the most significant byte is extracted on successive right shifts. Long values can be handled by defining a byte buffer of size eight.

	 
// read method
public static int readLittleEndianInteger(InputStream ips) throws IOException {
  int result;
  byte[] buffer = new byte[4];
  int check = ips.read(buffer);

  if (check != 4) {
    throw new IOException("Unexpected End of Stream");
  }
 
  int result = (buffer[3] << 24) | (buffer[2] << 16) | (buffer[1] << 8) | buffer[0];
  return result;
}

// write method
public static void writeLittleEndianInteger(int i, OutputStream ops) throws IOException {
  int result;
  byte[] buffer = new byte[4];
  buffer[0] = (byte) i;
  buffer[1] = (byte) (i >> 8);
  buffer[2] = (byte) (i >> 16);
  buffer[3] = (byte) (i >> 24);
  ops.write(buffer);
}

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In JDK 1.5+, the reverseBytes() methods method defined in the classes Character, Short, Integer and Long can be used to reverse the order of the bytes constituting the integer. Note that there is no such method for float and double values.

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