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UseLambdaForFunctionalInterface: only convert when the anonymous class implements the SAM by timtebeek · Pull Request #962 · openrewrite/rewrite-static-analysis · GitHub
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UseLambdaForFunctionalInterface: only convert when the anonymous class implements the SAM - #962

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tim/fix-issue-961
Aug 6, 2026
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UseLambdaForFunctionalInterface: only convert when the anonymous class implements the SAM#962
timtebeek merged 1 commit into
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tim/fix-issue-961

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@timtebeek timtebeek commented Aug 6, 2026 •
edited by moderne-meeseeks Bot
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What's wrong

UseLambdaForFunctionalInterface picked the interface's single abstract method (SAM) and then converted the anonymous class body without ever checking that the method the anonymous class declares is that SAM. When an anonymous class overrides a default method instead, the conversion produced code that fails to compile:

interface BusinessRule {
    void apply();

    default List<String> getConfigurationTexts() {
        return List.of();
    }
}

// before
BusinessRule rule = new BusinessRule() {
    @Override
    public List<String> getConfigurationTexts() {
        return List.of("zero", "one", "two");
    }
};

// after (invalid: implements apply(), not getConfigurationTexts())
BusinessRule rule = () -> List.of("zero", "one", "two");

The fix

shouldConvertToLambda now requires the declared method's name and parameter count to match the SAM, so overriding a default (or any non-SAM) method leaves the anonymous class alone.

Note on the test change

lambdaWithComplexTypeInference declared public Map<String, Integer> getObject() inside a new Supplier<Map<String, Integer>>() { ... } — that sample never compiles, since Supplier's method is get(). It only passed because the recipe wasn't checking the method name. Renamed to get(); the test still asserts the same cast-preserving transformation.

@timtebeek
UseLambdaForFunctionalInterface: only convert when the anonymous clas…
caf5539 
…s implements the SAM

An anonymous class that overrides a `default` method rather than the single
abstract method is not lambda-compatible; converting it produced code that
failed to compile with "X is not a functional interface".

Fixes #961
@github-project-automation github-project-automation Bot moved this to In Progress in OpenRewrite Aug 6, 2026
@timtebeek
timtebeek marked this pull request as ready for review August 6, 2026 12:21
@timtebeek
timtebeek merged commit 459a399 into main Aug 6, 2026
1 check passed
@timtebeek
timtebeek deleted the tim/fix-issue-961 branch August 6, 2026 12:21
@github-project-automation github-project-automation Bot moved this from In Progress to Done in OpenRewrite Aug 6, 2026
mergify Bot added a commit to robfrank/linklift that referenced this pull request Aug 20, 2026
@mergify
chore(deps): bump org.openrewrite.recipe:rewrite-static-analysis from…
04fc150 
… 2.40.0 to 2.41.0 [skip ci]

Bumps [org.openrewrite.recipe:rewrite-static-analysis](https://github.com/openrewrite/rewrite-static-analysis) from 2.40.0 to 2.41.0.
Release notes

*Sourced from [org.openrewrite.recipe:rewrite-static-analysis's releases](https://github.com/openrewrite/rewrite-static-analysis/releases).*

> 2.41.0
> ------
>
> What's Changed
> --------------
>
> * Pre-install the JavaScript RPC npm package before running tests by [`@​timtebeek`](https://github.com/timtebeek) in [openrewrite/rewrite-static-analysis#956](https://redirect.github.com/openrewrite/rewrite-static-analysis/pull/956)
> * UnnecessaryExplicitTypeArguments: retain witness for a return-only ty… by [`@​neil-mushell`](https://github.com/neil-mushell) in [openrewrite/rewrite-static-analysis#958](https://redirect.github.com/openrewrite/rewrite-static-analysis/pull/958)
> * Do not delete expressions that may have side effects by [`@​timtebeek`](https://github.com/timtebeek) in [openrewrite/rewrite-static-analysis#959](https://redirect.github.com/openrewrite/rewrite-static-analysis/pull/959)
> * OpenRewrite recipe best practices by [`@​timtebeek`](https://github.com/timtebeek) in [openrewrite/rewrite-static-analysis#960](https://redirect.github.com/openrewrite/rewrite-static-analysis/pull/960)
> * UseLambdaForFunctionalInterface: only convert when the anonymous class implements the SAM by [`@​timtebeek`](https://github.com/timtebeek) in [openrewrite/rewrite-static-analysis#962](https://redirect.github.com/openrewrite/rewrite-static-analysis/pull/962)
> * ReplaceStringBuilderWithString: wrap `char[]` appends in `String.valueOf` by [`@​martinfrancois`](https://github.com/martinfrancois) in [openrewrite/rewrite-static-analysis#977](https://redirect.github.com/openrewrite/rewrite-static-analysis/pull/977)
> * RemoveMethodsOnlyCallSuper: keep synchronized and deprecated overrides by [`@​martinfrancois`](https://github.com/martinfrancois) in [openrewrite/rewrite-static-analysis#971](https://redirect.github.com/openrewrite/rewrite-static-analysis/pull/971)
> * Make sure ModifierOrder doesn't alter Python's def quasi-modifier by [`@​greg-at-moderne`](https://github.com/greg-at-moderne) in [openrewrite/rewrite-static-analysis#981](https://redirect.github.com/openrewrite/rewrite-static-analysis/pull/981)
> * NullableOnMethodReturnType: only move annotations applicable to TYPE\_USE by [`@​martinfrancois`](https://github.com/martinfrancois) in [openrewrite/rewrite-static-analysis#968](https://redirect.github.com/openrewrite/rewrite-static-analysis/pull/968)
> * `FallThrough` to work only for Java files by [`@​greg-at-moderne`](https://github.com/greg-at-moderne) in [openrewrite/rewrite-static-analysis#982](https://redirect.github.com/openrewrite/rewrite-static-analysis/pull/982)
> * Retry a failed npx warm, and survive a machine without Node by [`@​timtebeek`](https://github.com/timtebeek) in [openrewrite/rewrite-static-analysis#984](https://redirect.github.com/openrewrite/rewrite-static-analysis/pull/984)
> * Make `DefaultComesLast` apply only to Java by [`@​greg-at-moderne`](https://github.com/greg-at-moderne) in [openrewrite/rewrite-static-analysis#983](https://redirect.github.com/openrewrite/rewrite-static-analysis/pull/983)
>
> New Contributors
> ----------------
>
> * [`@​martinfrancois`](https://github.com/martinfrancois) made their first contribution in [openrewrite/rewrite-static-analysis#977](https://redirect.github.com/openrewrite/rewrite-static-analysis/pull/977)
>
> **Full Changelog**: <openrewrite/rewrite-static-analysis@v2.40.0...v2.41.0>


Commits

* [`43b51de`](openrewrite/rewrite-static-analysis@43b51de) Make DefaultComesLast apply only to Java ([#983](https://redirect.github.com/openrewrite/rewrite-static-analysis/issues/983))
* [`5d08edd`](openrewrite/rewrite-static-analysis@5d08edd) Retry a failed npx warm, and survive a machine without Node ([#984](https://redirect.github.com/openrewrite/rewrite-static-analysis/issues/984))
* [`49ddf78`](openrewrite/rewrite-static-analysis@49ddf78) FallThrough to work only for Java files ([#982](https://redirect.github.com/openrewrite/rewrite-static-analysis/issues/982))
* [`9699a7e`](openrewrite/rewrite-static-analysis@9699a7e) NullableOnMethodReturnType: only move annotations applicable to TYPE\_USE ([#968](https://redirect.github.com/openrewrite/rewrite-static-analysis/issues/968))
* [`0c6f970`](openrewrite/rewrite-static-analysis@0c6f970) Make sure ModifierOrder doesn't alter Python's def quasi-modifier ([#981](https://redirect.github.com/openrewrite/rewrite-static-analysis/issues/981))
* [`6ef24c5`](openrewrite/rewrite-static-analysis@6ef24c5) RemoveMethodsOnlyCallSuper: keep synchronized and deprecated overrides ([#971](https://redirect.github.com/openrewrite/rewrite-static-analysis/issues/971))
* [`0d8f7d7`](openrewrite/rewrite-static-analysis@0d8f7d7) ReplaceStringBuilderWithString: wrap `char[]` appends in `String.valueOf` ([#977](https://redirect.github.com/openrewrite/rewrite-static-analysis/issues/977))
* [`9a15a92`](openrewrite/rewrite-static-analysis@9a15a92) OpenRewrite recipe best practices
* [`a394f54`](openrewrite/rewrite-static-analysis@a394f54) UnnecessaryExplicitTypeArguments: regression test for witness on varargs meth...
* [`0ecb6d8`](openrewrite/rewrite-static-analysis@0ecb6d8) Update Gradle wrapper to 9.7.0
* Additional commits viewable in [compare view](openrewrite/rewrite-static-analysis@v2.40.0...v2.41.0)
  
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Recipe UseLambdaForFunctionalInterface converts anonymous class to lambda and causes “not a functional interface” compile error

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