ClassCastLambdaUsage

SUGGESTION

Simplification

View source code on GitHub

Summary

Prefer Class::cast method reference over equivalent lambda expression

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("ClassCastLambdaUsage") to the enclosing element.

Disable this pattern completely by adding -Xep:ClassCastLambdaUsage:OFF as compiler argument. Learn more.

Samples

Replacement

Shows the difference in example code before and after the bug pattern is applied.

 import java.util.stream.Stream;
 
 class A {
   void m() {
-    Stream.of(1).map(i -> (Integer) i);
+    Stream.of(1).map(Integer.class::cast);
   }
 }
 

Identification

Shows code lines which will (not) be flagged by this bug pattern.
A //BUG: Diagnostic contains: comment is placed above any violating line.

import com.google.common.collect.ImmutableSet;
import java.util.stream.IntStream;
import java.util.stream.Stream;

class A {
  void m() {
    Number localVariable = 0;

    Stream.of(0).map(i -> i);
    Stream.of(1).map(i -> i + 1);
    Stream.of(2).map(Integer.class::cast);
    Stream.of(3).map(i -> (Integer) 2);
    Stream.of(4).map(i -> (Integer) localVariable);
    // XXX: Ideally this case is also flagged. Pick this up in the context of merging the
    // `ClassCastLambdaUsage` and `MethodReferenceUsage` checks, or introduce a separate check that
    // simplifies unnecessary block lambda expressions.
    Stream.of(5)
        .map(
            i -> {
              return (Integer) i;
            });
    Stream.<ImmutableSet>of(ImmutableSet.of(5)).map(s -> (ImmutableSet<Number>) s);
    Stream.of(ImmutableSet.of(6)).map(s -> (ImmutableSet<?>) s);
    Stream.of(7).reduce((a, b) -> (Integer) a);
    IntStream.of(8).mapToObj(i -> (char) i);

    // BUG: Diagnostic contains:
    Stream.of(8).map(i -> (Integer) i);
  }
}