捕获具有交集类型参数的可序列化 lambda 时出现 ClassCastException

Question

我复制了尝试使用类型变量类型交集捕获 lambda 时抛出的异常；具体来说，为了复制，我试图将 lambda 捕获为 F where <A, F extends Consumer<A> & Serializable>:

public class Consumers {

    public static <A, F extends Consumer<A> & Serializable>
    Consumer<A> serializable(F action) {
        return action;
    }

    public static <A> Consumer<A> vary(Consumer<? super A> action) {...}

    private static final Consumer<Object> DOES_NOTHING =
            serializable(a -> {});

    public static <A> Consumer<A> doesNothing() {
        return vary(DOES_NOTHING);
    }

    ...
}

Consumer<String> action = Consumers.doesNothing(); // throws class cast exception

下面是抛出异常的例子：

 java.lang.ClassCastException: [insert lambda name] cannot be cast to java.util.function.Consumer

我可以将 Consumers.serializable 与局部变量或实例变量一起使用；尝试初始化静态变量时抛出此异常。

这是正确的行为吗？我正在使用最新的 Eclipse Oxygen，JDK u112。

Answer 1

这不应该被允许：javac 抱怨：

Consumers.java:??: error: incompatible types: cannot infer type-variable(s) A,F
            serializable(a -> {});
                        ^
    (argument mismatch; Consumer<Object> cannot be converted to INT#1)
  where A,F are type-variables:
    A extends Object declared in method <A,F>serializable(F)
    F extends Consumer<A>,Serializable declared in method <A,F>serializable(F)
  where INT#1 is an intersection type:
    INT#1 extends Object,Serializable,Consumer<Object>

它实际上是一个Eclipse编译器bug, fixed in 4.6 M6 (Neon), and it has already been noticed in this 。

捕获具有交集类型参数的可序列化 lambda 时出现 ClassCastException

ClassCastException when capturing a serializable lambda with intersection type parameters

lambda

java-8

intersection

classcastexception

type-variables