Question

那么，为什么这段代码会编译？

public static void main(String[] args) {
    Calculator test = (Calculator & Sumator) (a, b) -> a + b;
    System.out.println(test.calculate(2, 3));

    Sumator sumator = (Calculator & Sumator) (a, b) -> a + b; // does compile, but throws an Exception
    sumator.test();

    Both both = (Both) (a, b) -> a + b; // does not compile
}

interface Calculator {
    public int calculate(int a, int b);
}

interface Sumator {
    public int test();

    public int test3(int a, int b);
}

// intersection of both types
interface Both extends Sumator, Calculator {

}

这有点误导，我知道如何投射到交叉类型，我已经阅读了jls，但仍然令人困惑。

为什么

是有道理的

 Serializable & Comparable

会编译，因为这两者之间的结果（合成类型）是一个功能接口，但为什么会这样做：

 Calculator & Sumator

的作品？合成类型不是功能接口。

Answer 1

这是一个bug in Eclipse已经针对里程碑6修复了Eclipse Neon（4.6）。

Answer 2

好吧，它似乎是一个Eclipse编译器错误，因为它不能在javac下编译。我想知道如何解决这个问题，或者是否已经为此打开了一个问题。

   MultipleCastsBound.java:5: error: incompatible types: INT#1 is not a functional interface
        Calculator test = (Calculator & Sumator) (a, b) -> a + b;
                                                 ^
    multiple non-overriding abstract methods found in interface INT#1
  where INT#1 is an intersection type:
    INT#1 extends Object,Calculator,Sumator
MultipleCastsBound.java:8: error: incompatible types: INT#1 is not a functional interface
        Sumator sumator = (Calculator & Sumator) (a, b) -> a + b;
                                                 ^
    multiple non-overriding abstract methods found in interface INT#1
  where INT#1 is an intersection type:
    INT#1 extends Object,Calculator,Sumator
2 errors

Lambda和cast交叉类型（Eclipse编译器bug）

2 个答案: