Nullabilityanalyse

Nullabilityanalyse, or nullability analysis, is a static program analysis that determines, at various points in a program, whether an expression or reference can be null. The primary goal is to prevent null dereferences by identifying potential null values before runtime and to guide proper handling of nulls through annotations or type systems.

Techniques rely on data-flow analysis over the program's control-flow graph. Variants include flow-sensitive versus flow-insensitive analysis, and sometimes context- or interprocedural analysis. The analysis typically models a lattice of nullability values (for example, null, non-null, and unknown) and propagates constraints along assignments, conditionals, method calls, and returns. In many ecosystems it also infers or checks nullability annotations (such as Nullable and NonNull) or nullable types (for example, ? versus non-null types).

Applications include compiler checks, static analyzers, and API design aids. Tools and languages that employ nullability analysis include Kotlin and Java ecosystems with the Checker Framework or SpotBugs, as well as other languages with explicit nullability support. The analysis often supports reporting potential issues and guiding developers to add or refine annotations, or to introduce safer APIs or optional wrappers.

Limitations surround precision and performance. Aliasing, reflection, dynamic features, generics, and incomplete libraries can yield false positives or negatives. Interprocedural and path-sensitive variants improve precision but incur higher cost. Nullability analysis is typically complementary to runtime checks and to more expressive type systems that enforce null-safety.