How to Convert Int to Unsigned Byte and Back
Java 8 provides Byte.toUnsignedInt
to convert byte
to int
by unsigned conversion. In Oracle's JDK this is simply implemented as return ((int) x) & 0xff;
because HotSpot already understands how to optimize this pattern, but it could be intrinsified on other VMs. More importantly, no prior knowledge is needed to understand what a call to toUnsignedInt(foo)
does.
In total, Java 8 provides methods to convert byte
and short
to unsigned int
and long
, and int
to unsigned long
. A method to convert byte
to unsigned short
was deliberately omitted because the JVM only provides arithmetic on int
and long
anyway.
To convert an int back to a byte, just use a cast: (byte)someInt
. The resulting narrowing primitive conversion will discard all but the last 8 bits.
If you just need to convert an expected 8-bit value from a signed int to an unsigned value, you can use simple bit shifting:
int signed = -119; // 11111111 11111111 11111111 10001001/** * Use unsigned right shift operator to drop unset bits in positions 8-31 */int psuedoUnsigned = (signed << 24) >>> 24; // 00000000 00000000 00000000 10001001 -> 137 base 10/** * Convert back to signed by using the sign-extension properties of the right shift operator */int backToSigned = (psuedoUnsigned << 24) >> 24; // back to original bit pattern
http://docs.oracle.com/javase/tutorial/java/nutsandbolts/op3.html
If using something other than int
as the base type, you'll obviously need to adjust the shift amount: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html
Also, bear in mind that you can't use byte
type, doing so will result in a signed value as mentioned by other answerers. The smallest primitive type you could use to represent an 8-bit unsigned value would be a short
.