相关疑难解决方法(0)

我正在玩java8 lambdas,我遇到了编译器错误,我没想到.

假设我有一个函数interface A,一个abstract class B和一个class C重载方法,它们可以采用A或B作为参数:

public interface A { 
  void invoke(String arg); 
}

public abstract class B { 
  public abstract void invoke(String arg); 
}

public class C {
  public void apply(A x) { }    
  public B apply(B x) { return x; }
}

然后我可以传入一个lambda c.apply,它正确地解决了c.apply(A).

C c = new C();
c.apply(x -> System.out.println(x));

但是当我更改B作为泛型版本的参数的重载时,编译器报告两个重载是不明确的.

public class C {
  public void apply(A x) { …

我遇到一个奇怪的问题,方法引用Thread::sleep是模糊的,但具有相同签名的方法不是.

package test;    

public class Test
{
    public static void main(String[] args)
    {
        foo(Test::sleep, 1000L); //fine
        foo((FooVoid<Long>)Thread::sleep, 1000L); //fine
        foo(Thread::sleep, 1000L); //error
    }

    public static void sleep(long millis) throws InterruptedException
    {
        Thread.sleep(millis);
    }

    public static <P, R> void foo(Foo<P, R> function, P param) {}

    public static <P> void foo(FooVoid<P> function, P param) {}

    @FunctionalInterface
    public interface Foo<P, R> {
        R call(P param1) throws Exception;
    }

    @FunctionalInterface
    public interface FooVoid<P> {
        void call(P param1) throws Exception;
    }
}

我得到了这两个错误: …

使用Java 8,我得到以下代码的编译器错误:

public class Ambiguous {
    public static void call() {
        SomeDataClass data = new SomeDataClass();
        callee(data, SomeDataClass::getString);
        // compiler errors:
        // 1. at callee method name:
        // The method callee(SomeDataClass, Function<SomeDataClass,String>) is ambiguous for the type Ambiguous
        // 2. at lambda:
        // Type mismatch: cannot convert from boolean to String
        callee(data, d -> d.getRandom() > 0.5);
    }

    public static void callee(SomeDataClass data, Function<SomeDataClass, String> extractString) {
        System.out.println(extractString.apply(data));
    }

    public static void callee(SomeDataClass data, Predicate<SomeDataClass> check) {
        System.out.println(check.test(data));
    }
} …