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This article shows you what the high-order functions in Java8 and Scala are, which are concise and easy to understand, which will definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

The biggest advantage of function text is that it can be transmitted like other text (literal) such as strings or objects. This feature offers unlimited possibilities for building highly compact and reusable code. What are the higher-order functions in Java8 and Scala?

What are the higher order functions in Java8 and Scala

When we send a function text to a method, the most important thing we do is a method that receives method parameters (this is really around-_-|). This kind of method is called a high-order function. The addActionListener method mentioned in the Swing example above falls into this category. We can also define our own higher-order functions to provide ourselves with a lot of convenience. Let's look at a simple example:

Defmeasure [T] (func:= > T): t {

Valstart=System.nanoTime ()

Valresult=func

Valelapsed=System.nanoTime ()-start

Print ("Theexecutionofthiscalltook:%sns" .format (elapsed))

Result

}

In this example, we declare the time it takes for a method named measure to calculate the callback of the function text named func. The signature (signature) of the func method is that it takes no arguments and returns a generic type T. As you can see, functions in Scala don't necessarily need arguments, although they can-- and often do.

Now we can pass any function text (or method) to the measure method.

DefmyCallback= {

Thread.sleep (1000)

"Ijusttookapoewrnap"

}

Valresult=measure (myCallback)

> Theexecutionofthiscalltook:100244900ns

From a conceptual point of view, what we do is to distinguish the computational method call time from the actual operation. We constructed two code blocks (measure and myCallback) that can be reused, loosely coupled and similar to interceptor.

2. Reuse through high-order functions

Let's start with a hypothetical example where two reusable constructs are slightly tightly coupled:

DefdoWithContact (fileName:String,handle:Contact= > Unit): Unit= {

Try {

ValcontactStr=io.Source.fromFile (fileName). MkString

Valcontact=AContactParser.parse (contactStr)

Handle (contact)

}

Catch {

Casee:IOException= > println ("couldn'tloadcontactfile:" + e)

Casee:ParseException= > println ("coulnd'tparsecontactfile:" + e)

}

}

What are the higher order functions in Java8 and Scala

The doWithContact method reads contact information such as an electronic business card from a file and then provides the data to a parser (parser) to convert the data into objects in the contact domain. This object is then passed to a function text callback handle.doWithContact method and both function text returns a Unit type, which is equivalent to the method in java that returns void.

Now we can define various callback functions that can be passed to doWithContact:

ValstoreCallback= (c:Contact) = > ContactDao.save (c)

ValsendCallback= (c:Contact) = > {

ValmsgBody=AConverter.convert (c)

RestService.send (msgBody)

}

ValcombineCallback= (c:Contact) = > {

StoreCallback (c)

SendCallback (c)

}

DoWithContact ("custerX.vcf", storeCallback)

DoWithContact ("custerY.vcf", sendCallback)

DoWithContact ("custerZ.vcf", combineCallback)

DoWithContact ("custerZ.vcf", combineCallback)

Callback functions can also be passed inline:

DoWithContact ("custerW.vcf", (c:Contact) = > ContactDao.save (c))

3. Higher order functions in Java8

The equivalent implementation in java8 looks very similar-- using the current syntax advice:

PublicinterfaceBlock {

Voidapply (Tt)

}

PublicvoiddoWithContact (StringfileName,Blockblock) {

Try {

StringcontacStr=FileUtils.readFileToString (newFile (fileName))

Contact.apply (contact)

Block.apply (contact)

}

Catch (IOExceptione) {

System.out.println ("cloudn'tloadcontactfile:" + e.getMessage ())

}

Catch (ParseExceptione) {

System.out.println ("cloudn'tparsecontactfile:" + e.getMessage ())

}

}

/ / usage

DoWithContact ("custerX.vcf", c-> ContactDao.save (c))

4. Benefits of using higher-order functions

As you can see, functions help us to cleanly distinguish between object creation and processing. In this way, new business logic processing objects can be easily added without having to be coupled with the object creation logic.

As a result, we keep our code DRY (Dont'tRepeatYourself) by using higher-order functions, so programmers can get the best benefit from a very fine-grained code reuse.

What are the higher-order functions in Java8 and Scala? have you learned any knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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