JAVA8 之 Method References－Java in a Nutshell, 6th

JAVA8 的函數引用和 lambda表達式的關係＝＞函數引用是一種簡化的 lambda表達式，只給出現有的函數，參數和返回值編譯器推斷去吧．

　其實這語法和 lambda表達式正好相反， lambda表達式表示匿名方法，就是沒有函數名，只給出參數和方法體．那麼現有的函數就派上用場了，現有的函數有方法名，給出方法名，參數和方法體都已經有了，由編譯器推斷出．

注：java中的方法不能獨立存在，必須包含在類型中，這就是 lambda表達式 @FunctionalInterface的限制．

Recall that we can think of lambda expressions as methods that don’t have names.

Now, consider this lambda expression:

// In real code this would probably be shorter because of type inference

(MyObject myObj) -> myObj.toString()

This will be autoconverted to an implementation of a @FunctionalInterface that

has a single nondefault method that takes a single MyObject and returns String.

However, this seems like excessive boilerplate, and so Java 8 provides a syntax for

making this easier to read and write:

MyObject::toString

This is a shorthand, known as a method reference, that uses an existing method as a

lambda expression. It can be thought of as using an existing method, but ignoring

the name of the method, so it can be can used as a lambda, and autoconverted in the

usual way.