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Use @MonotonicNonNull for lazily-initialized fields

io.moderne.nullability.cleanup.UseMonotonicNonNullForLazyInitializedField

Annotates a lazily-initialized field with the Checker Framework @org.checkerframework.checker.nullness.qual.MonotonicNonNull annotation, which NullAway recognises as the idiomatic contract for a field that is set the first time it is needed and never reset to null afterward. NullAway flags a non-null instance field that is not assigned in the constructor; for such a lazily-initialized field @MonotonicNonNull is the correct fix rather than @Nullable, because the field is non-null after first use, so readers should not be forced to handle null. A field qualifies when at least one assignment to it is guarded by a f == null (or this.f == null) check, it is never assigned null anywhere except an explicit = null declaration initializer, and it is not assigned a non-null value at its declaration or unconditionally in a constructor. Conservative by design: it skips primitive, final, static, and already-annotated fields, fields assigned null outside their initializer (genuinely @Nullable — left for AddNullableToField), and fields assigned non-null unconditionally. Kotlin and Groovy express field nullability in the type system, which their compilers already enforce, so those sources are generally left unchanged.

Recipe source​

This recipe is only available to users of Moderne.

This recipe is available under the Moderne Proprietary License.

Used by​

This recipe is used as part of the following composite recipes:

Example​

Before​
class Test {
    private String cache;

    String get() {
        if (cache == null) {
            cache = compute();
        }
        return cache;
    }

    String compute() {
        return "x";
    }
}
After​
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;

class Test {
    @MonotonicNonNull
    private String cache;

    String get() {
        if (cache == null) {
            cache = compute();
        }
        return cache;
    }

    String compute() {
        return "x";
    }
}

Usage​

This recipe has no required configuration options. Users of Moderne can run it via the Moderne CLI.

You will need to have configured the Moderne CLI on your machine before you can run the following command.

shell
mod run . --recipe UseMonotonicNonNullForLazyInitializedField

If the recipe is not available locally, then you can install it using:

mod config recipes jar install io.moderne.recipe:rewrite-nullability:0.1.0

See how this recipe works across multiple open-source repositories​

Run this recipe on OSS repos at scale with the Moderne SaaS.

The community edition of the Moderne platform enables you to easily run recipes across thousands of open-source repositories.

Please contact Moderne for more information about safely running the recipes on your own codebase in a private SaaS.

Data Tables​

Source files that had results​

org.openrewrite.table.SourcesFileResults

Source files that were modified by the recipe run.

Column NameDescription
Source path before the runThe source path of the file before the run. null when a source file was created during the run.
Source path after the runA recipe may modify the source path. This is the path after the run. null when a source file was deleted during the run.
Parent of the recipe that made changesIn a hierarchical recipe, the parent of the recipe that made a change. Empty if this is the root of a hierarchy or if the recipe is not hierarchical at all.
Recipe that made changesThe specific recipe that made a change.
Estimated time savingAn estimated effort that a developer to fix manually instead of using this recipe, in unit of seconds.
CycleThe recipe cycle in which the change was made.