当类实现相同的接口时，Lambda表达式因LambdaConversionException而失败？ [重复]

Posted 2021-05-04

这个问题在这里已有答案：

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• LambdaConversionException with generics: JVM bug? 4个答案

我很惊讶，为什么lambda表达式无法在运行时正确调用。这是一个类型推断错误？工作aournd示例取消注释显式类型参数声明。

public class LambdaConversionTest {
    @Test
    public void whyDidLambdaExpressionFailsWithLambdaConversionException() {
        try {
            //      v--- when uncomment it, the behavior is what I expected
            Stream./*<Collector>*/of(new Robot(), new Puller())
                  .flatMapToInt(Collector::stream).sum();
            fail("fails with expected behavior");
        } catch (BootstrapMethodError why) {
            assertThat(why.getCause().getMessage()
                 ,containsString("Invalid receiver type interface "));
        }
    }

    interface Marker {
    }

    interface Collector {
        IntStream stream();
    }

    class Robot implements Collector, Marker {
        @Override
        public IntStream stream() {
            return IntStream.empty();
        }
    }

    class Puller implements Collector, Marker {
        @Override
        public IntStream stream() {
            return IntStream.empty();
        }
    }
}

答案

对于这个特殊的this JDK bug实例，应该注意的是，如果你在Marker之后声明接口Collector它不会失败

失败：

interface Marker {}

interface Collector {
    IntStream stream();
}

通过：

interface Collector {
    IntStream stream();
}
interface Marker {}