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Today, I will talk to you about how to achieve function input parameters in Java8, many people may not know much about it. In order to make you understand better, the editor has summarized the following content for you. I hope you can get something according to this article.

1. Previously on

Java8 supports passing a function as an argument to another function, and this usage was briefly mentioned in the first learning note. But in the first study, I was still confused. Let's talk about my confusion first.

Function input parameters are mentioned in the first article, and the type of input parameters should first define an API:

Public interface Predicate {boolean test (T t);}

Then define a function as follows:

Public static List filterApples (List inventory,Predicate predicate) {List result = new ArrayList (); for (Apple apple:inventory) {if (predicate.test (apple)) {result.add (apple);}} return result;}

Finally, the method is called:

List filterGreenApples= filterApples (originApples,Apple::isGreenApple)

Here comes the problem: the input parameter type is an interface Predicate, so shouldn't the actual input parameter be the object of the implementation class of this interface? why just pass this static method?

With this question in mind, let's continue to learn the function input parameter.

two。 Continue to learn

To figure out what a function is passed as an argument, you have to start with the simplest implementation. When learning design patterns, I have learned about strategic patterns. In the first article, Apple's demo is taken as an example, plus the strategy mode.

First define an interface based on which all subsequent policies are implemented:

Public interface ApplePredicate {boolean test (T t);}

Then two strategies for filtering apples are implemented: one is to filter by color, and the other is to filter by weight:

Public class filterAppleByColorPredicate implements Predicate {@ Override public boolean test (Apple apple) {return "green" .equals (apple.getColor ());} public class filterAppleByWeightPredicate implements Predicate {@ Override public boolean test (Apple apple) {return apple.getWeight () > 15;}}

Finally, the main method is implemented as follows:

Public static void main (String [] args) {List inventory =...; / / Select a policy to filter by color ApplePredicate colorPredicate = new filterAppleByColorPredicate (); filterApples (inventory,colorPredicate); / / Select a policy to filter by weight ApplePredicate weightPredicate = new filterAppleByWeightPredicate (); filterApples (inventory,weightPredicate);} public static List filterApples (List inventory,ApplePredicate predicate) {List result = new ArrayList () For (Apple apple:inventory) {if (predicate.test (apple)) {result.add (apple);}} return result;}

This implements a code based on the policy pattern.

3. Anonymous class

On the basis of the second section, anonymous classes are used directly, omitting the definition of implementation classes for various policies:

FilterApples (inventory,new ApplePredicate () {public boolean test (Apple apple) {return "green" .equals (apple.getColor ());}}); 4. Lambda expression

The third section uses anonymous classes, but it is still cumbersome when there is more code in the contemporary era, so Lambda expressions are introduced to simplify writing:

FilterApples (inventory, (Apple apple)-> "green" .equals (apple.getColor ()

I still have questions about Lambda here, if the interface defines two methods:

Public interface ApplePredicate {boolean test (T t); boolean test2 (T t);} after reading the above, do you have any further understanding of how to implement function input in Java8? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

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