在Java中导出函数对象的最佳实践是什么？

Question

在Java中创建function objects （导出一个适用于其他对象的单个方法的无状态对象）的最佳实践是什么？

Answer 1

It's instructive to look at the forthcoming Java 8 functional interfaces

The Java 8 class library has a new package, java.util.functions, which contains several new functional interfaces. Many of these can be used with the Collections API.

If you follow the patterns exhibited here, you'll have a functional interface (an interface supporting one method) and an implementation with no members. Your function object shouldn't call any methods on the method arguments that could change their state (ie exhibit side-effects). Unfortunately you can't enforce that - you have to rely on convention for this.

Answer 2

Java是面向对象的编程语言，因此使用策略设计模式。

Answer 3

Java8 should have lambdas to ease the creation of functional interface implementations. Before Java8 you may look at what the guava library offers: Functional Explained

Here is an excerpt of the documentation:

Guava provides two basic "functional" interfaces: Function, which has the single method B apply(A input). Instances of Function are generally expected to be referentially transparent -- no side effects -- and to be consistent with equals, that is, a.equals(b) implies that function.apply(a).equals(function.apply(b)). Predicate, which has the single method boolean apply(T input). Instances of Predicate are generally expected to be side-effect-free and consistent with equals.

Answer 4

Ok after commenting, here is an answer: There is no easy/convenient way to pass a function.

Most of the time you will declare an inner class which implements a interface like for example, the Comparator : http://docs.oracle.com/javase/6/docs/api/java/util/Comparator.html

The fact that functions cannot be passed as parameters gave rise to a lot of so called design patterns, where you pass around objects classes/interfaces which declare having those functions.

As mentioned by others life will get a little easier with Java 8.