Syntax for specifying a method reference to a generic method

问题

I read the following code in "Java - The beginner's guide"

interface SomeTest <T>
{
    boolean test(T n, T m);
}

class MyClass
{
    static <T> boolean myGenMeth(T x, T y)
    {
        boolean result = false;
        // ...
        return result;
    }
}

The following statement is valid

SomeTest <Integer> mRef = MyClass :: <Integer> myGenMeth;

Two points were made regarding the explanation of the above code

1 - When a generic method is specified as a method reference, its type argument comes after the :: and before the method name.

2 - In case in which a generic class is specified, the type argument follows the class name and precedes the ::.

My query:-

The code above is the example of the first quoted point

Can someone provide me an example of code which implement the second quoted point?

(Basically I don't understand the second quoted point).

回答1:

The second quoted point just means that the type parameter belongs to the class. For example:

class MyClass<T>
{
    public boolean myGenMeth(T x, T y)
    {
        boolean result = false;
        // ...
        return result;
    }
}

This would then be called like this:

SomeTest<Integer> mRef = new MyClass<Integer>() :: myGenMeth;

回答2:

For example

  Predicate<List<String>> p = List<String>::isEmpty;

Actually we don't need the type argument here; the type inference will take care of

  Predicate<List<String>> p = List::isEmpty;

But in cases type inference fails, e.g. when passing this method reference to a generic method without enough constraints for inference, it might be necessary to specify the type arguments.

来源：https://stackoverflow.com/questions/31245127/syntax-for-specifying-a-method-reference-to-a-generic-method

标签

java

generics

method-reference