The only unsigned primitive integer type in Java is the 16-bit
char data type; all of the other primitive integer types are signed. To interoperate with native languages, such as C or C++, that use unsigned types extensively, any unsigned values must be read and stored into a Java integer type that can fully represent the possible range of the unsigned data. For example, the Java
long type can be used to represent all possible unsigned 32-bit integer values obtained from native code.
Noncompliant Code Example
This noncompliant code example uses a generic method for reading integer data without considering the signedness of the source. It assumes that the data read is always signed and treats the most significant bit as the sign bit. When the data read is unsigned, the actual sign and magnitude of the values may be misinterpreted.
This compliant solution requires that the values read are 32-bit unsigned integers. It reads an unsigned integer value using the
readInt() method. The
readInt() method assumes signed values and returns a signed
int; the return value is converted to a
long with sign extension. The code uses an
& operation to mask off the upper 32 bits of the
long, producing a value in the range of a 32-bit unsigned integer, as intended. The mask size should be chosen to match the size of the unsigned integer values being read.
As a general principle, you should always be aware of the signedness of the data you are reading.
Treating unsigned data as though it were signed produces incorrect values and can lead to lost or misinterpreted data.
Automated detection is infeasible in the general case.
Chapter 2, "Primitive Data Types, Cross-Platform Issues, Unsigned Integers"
Section 2.4.5, "Accessing Unsigned Data"
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