Ciri dan Kelebihan Groovy Over Java

Groovy ialah bahasa dinamik yang dibina untuk JVM. Ia disepadukan dengan lancar dengan kod Java dan perpustakaan, membina kekuatan Java sambil menambah ciri yang diilhamkan oleh bahasa seperti Python dan Ruby.
Tidak seperti bahasa pengaturcaraan bebas seperti C, C atau Python, Groovy bergantung pada Java. Ciri-ciri baru yang diperkenalkan di Jawa juga diterima pakai dalam Groovy. Matlamat utama Groovy adalah untuk mengurangkan tugasan berulang dan kod boilerplate, menjadikannya pilihan terbaik untuk skrip pada JVM.

Perbezaan antara Jawa

Java, yang terkenal dengan ciri teguhnya, sering dianggap sebagai bahasa pengaturcaraan yang kompleks dan berat. Sebaliknya, Groovy menawarkan pendekatan yang lebih diperkemas kepada pembangunan Java. Sebagai bahasa berasaskan JVM dengan kedua-dua keupayaan menaip statik dan dinamik, Groovy memudahkan banyak aspek pengekodan.

Pembangun Java biasanya mendapati Groovy mudah diambil, membolehkan mereka meningkatkan set kemahiran mereka dengan cepat dan memanjangkan kefungsian Java. Kelebihan ketara Groovy ialah reputasinya untuk memudahkan ujian unit.

Pertimbangkan program di bawah dan mari tafsirkan perbezaan dalam output daripada Java dan Groovy.

int method(String arg) {
    return 1;
}
int method(Object arg) {
    return 2;
}
Object o = "Object"; 
int result = method(o);

Kaedah di atas memberikan output yang berbeza dalam Java dan Groovy.

Output

Keluaran Java : 2
Keluaran groovy : 1

Ini berlaku kerana,
Di Java, lebihan kaedah diselesaikan pada masa kompilasi berdasarkan jenis masa kompilasi argumen.
Walau bagaimanapun, dalam kaedah groovy, resolusi berlaku pada masa jalan.

Perbezaan ketara lain antara Java dan Groovy ialah,

Import Lalai:
Groovy menyediakan satu set import lalai untuk pakej yang biasa digunakan, yang boleh memudahkan kod dan mengurangkan keperluan untuk pernyataan import eksplisit. Contohnya, Groovy mengimport kelas secara automatik daripada pakej seperti java.util, java.io dan groovy.lang, antara lain. Sebaliknya, Java memerlukan semua import yang diperlukan untuk dinyatakan dengan jelas.

Penutupan

Penutupan ialah blok bebas kod yang boleh menerima parameter dan melaksanakan kod. Mereka boleh ditulis sekali dan digunakan kemudian. Tidak seperti kaedah atau fungsi standard, penutupan boleh menangkap dan menggunakan pembolehubah daripada konteks sekelilingnya. Walaupun secara teknikal, tidak terdapat banyak perbezaan antara objek dan penutupan, penutupan meningkatkan kebolehbacaan dan fleksibiliti kod dengan ketara.

Penutupan panggilan

Penutupan groovy boleh digunakan dalam dua cara.

• Boleh dipanggil seperti fungsi biasa.
• Menggunakan kaedah .call() untuk Penutupan.

def sumTwoNums = {
    a,b -> 
    println "Adding ${a} and ${b}"
    return a+b
}

println sumTwoNums(2,4)
println sumTwoNums.call(5,2)

Output

6

def updateCounter = {
    def counter = 0
    return {
        return counter = counter + 1;
    }
}

def updateCounterFunc = updateCounter.call()

println updateCounterFunc()
println updateCounterFunc()

Output

1
2

Dalam program di atas, updateCounter mentakrifkan pembilang pembolehubah setempat dan mengembalikan penutupan lain. Penutupan yang dikembalikan mempunyai akses kepada pembolehubah kaunter kerana cara penutupan menangkap konteks sekelilingnya yang diterangkan kemudian dalam blog ini.

Apabila updateCounter.call() dilaksanakan, ia memulakan pembilang kepada 0 dan mengembalikan penutupan baharu yang menambah pembilang sebanyak 1 setiap kali ia dipanggil.

Ciri-ciri Penutupan

Untuk memahami sepenuhnya penutupan secara groovy, kita perlu memahami apakah ini dan pemilik penutupan.

ini

Dalam groovy, kata kunci ini merujuk kepada kelas yang disertakan. Sebagai contoh, jika kita mengakses ini di dalam penutupan yang terdapat di dalam kelas sebut Pengguna, maka ini akan merujuk kepada kelas Pengguna.

Jika kita menggunakan ini di dalam penutupan yang bersarang dalam penutupan lain dan kedua-dua penutupan ini terdapat di dalam kelas, maka ini merujuk kepada kelas luar yang terdekat.

pemilik

Pemilik penutupan adalah serupa dengan ini, tetapi kata kunci pemilik merujuk kepada objek penutup atau penutupan penutupan.

Mari kita lihat contoh untuk memahami dengan jelas pemilik dan penutupan ini.

class Example{
    def outerClosure = {
        def innerClosure = {
            println "Inner closure ---> $this"
        }
        innerClosure()
        println "Outer closure ---> $this"
    }

    def printCurrentObject(){
        println "Current object ---> $this"
    }
}

Example example = new Example()

example.outerClosure.call()

example.printCurrentObject()

Output

Penutupan dalaman ---> Contoh@6e57e95e
Penutupan luar ---> Contoh@6e57e95e
Objek semasa ---> Contoh@6e57e95e

Dalam penutupan bersarang di atas diisytiharkan, walaupun berbilang lapisan penutupan terlibat, rujukan kepada objek semasa (ini) masih menunjuk kepada contoh kelas luar. Ini membenarkan akses kepada sifat dan kaedah kelas yang disertakan dari dalam mana-mana penutupan bersarang.

class Example{
    def outerClosure = {
        def innerClosure = {
            println "Inner closure owner ---> " + getOwner()
        }
        innerClosure()
        println "Outer closure owner ---> " + getOwner()
    }

    def printThis(){
        println "Current object ---> $this"
    }
}

Example example = new Example()

example.outerClosure.call()

example.printThis()

Output

Pemilik penutup dalaman ---> Contoh$_closure1@410954b
Pemilik penutup luar ---> Contoh@46cc127b
Objek semasa ---> Contoh@46cc127b

Inner Closure Owner:
The innerClosure is enclosed within the outerClosure, so getOwner() in the innerClosure returns the outerClosure.

Outer Closure Owner:
The outerClosure itself is enclosed within the instance of the Example class. Therefore, getOwner() in the outerClosure returns the Example class instance

Delegation

In Groovy, delegation is a mechanism that allows an object to pass on method calls to another object (known as the delegate). This concept is particularly useful when working with closures. Groovy provides the delegate property in closures to allow you to specify another object that will handle method calls not defined within the closure.

The below is an example of how delegation works in groovy

class ServiceLogger{
    def log(message){
        println "Service: $message"
    }
}

class DatabaseLogger{
    def log(message){
        println "Database: $message"
    }
}

def logMessage = {
    log(it)
}

logMessage.delegate = new ServiceLogger()     -> 1

logMessage("User created successfully")

logMessage.delegate = new DatabaseLogger()

logMessage("User fetched from DB successfully")

Output

Service: User created successfully
Database: User fetched from DB successfully

In the above example, there are two classes ServiceLogger and DatabaseLogger and a closure named logMessage.

First we are assigning the ServiceLogger as a delegate for the closure. So when the closure logMessage is called then the delegate's (log) function is invoked. Later when we change the delegate of the closure to DatabaseLogger the log method present inside the DatabaseLogger is invoked.

Let's see another example to understand delegation in detail.

class MediaPlayer{
    def fileName
    def play = { "Playing ${fileName}" }
}

class VideoPlayer{
    def fileName
}

MediaPlayer mediaPlayer = new MediaPlayer(fileName:"theme-music.mp3")
VideoPlayer videoPlayer = new VideoPlayer(fileName:"trailer.mp4")

println mediaPlayer.play()

mediaPlayer.play.delegate = videoPlayer

println mediaPlayer.play()

Initially, when mediaPlayer.play() is called, it uses the fileNamefrom the MediaPlayer instance, resulting in the output: Playing theme-music.mp3. Even after changing the delegate of the closure to VideoPlayer, the play closure still prints the MediaPlayer file name. This behaviour is due to the default delegation strategy in Groovy closures. To understand this, let's explore the different delegation strategies in Groovy closures.

Delegation Strategy

In Groovy, the delegation strategy defines how a closure resolves method calls or property references that are not explicitly defined within the closure itself.

Groovy provides several delegation strategies that dictate how a closure resolves calls to methods or properties:

Closure.OWNER_FIRST (default): The closure first tries to resolve the call in the owner, then the delegate.
Closure.DELEGATE_FIRST: The closure first looks for the method/property in the delegate, and if not found, it checks in the owner.
Closure.OWNER_ONLY: The closure only looks for method/property in the owner and ignores the delegate.
Closure.DELEGATE_ONLY: The closure only resolves method/property in the delegate and ignores the owner.

So in the above program though we have changed the delegate of the closure while executing the closure will use its owner's methods or properties. Here the owner of the closure play is MediaPlayer.

class MediaPlayer{
    def fileName
    def play = { "Playing ${fileName}" }
}

class VideoPlayer{
    def fileName
}

MediaPlayer mediaPlayer = new MediaPlayer(fileName:"theme-music.mp3")
VideoPlayer videoPlayer = new VideoPlayer(fileName:"trailer.mp4")

println mediaPlayer.play()

mediaPlayer.play.resolveStrategy = Closure.DELEGATE_FIRST
mediaPlayer.play.delegate = videoPlayer

println mediaPlayer.play()

Output

Playing theme-music.mp3
Playing trailer.mp4

Here we have changed the resolution strategy of the closure to DELEGATE_FIRST, now the closure uses the delegate's methods and properties.

Another advantage of using Closures is lazy evaluation of strings. Here is an example

def name = "Walter"
def greetingMsg = "Welcome! ${name}"

name = "White"

println greetingMsg

Output

Welcome! Walter

def name = "Walter"
def greetingMsg = "Welcome! ${->name}"

name = "White"

println greetingMsg

Output

Welcome! White

In the first script, the GString ${name} is evaluated when greetingMsg is defined, capturing the value of name at that moment, which is "Walter".

In the second script, the GString ${->name} uses a closure. The closure is evaluated at the moment of printing, not when greetingMsg is defined. Since name has changed to "White" by the time the closure is executed, it reflects the updated value.

Currying in Groovy

Currying in Groovy is a technique that allows you to create a new closure by pre-filling some of the parameters of an existing closure. This effectively reduces the number of arguments needed to call the new closure, making it a convenient way to create specialized functions from a general one.

def getUsers = { groupId, role, status ->
    // Simulate fetching users from a database or API
    println "Fetching users from group ${groupId} with role ${role} and status ${status}"
}

def getHRUsers = getUsers.curry("HR")

getHRUsers("Admin", "Active")
getHRUsers("Viewer", "Inactive")

def getActiveUsers = getUsers.rcurry("ACTIVE")

getActiveUsers("Development", "Tester")

def getAllDevelopers = getUsers.ncurry(1, "Developer")

getAllDevelopers("IT", "Active")
getAllDevelopers("Marketing", "Suspended")

Output

Fetching users from group HR with role Admin and status Active
Fetching users from group HR with role Viewer and status Inactive
Fetching users from group Development with role Tester and status ACTIVE
Fetching users from group IT with role Developer and status Active
Fetching users from group Marketing with role Developer and status Suspended

In Groovy, there are three currying methods used to partially apply parameters to closures:

curry(): Fixes the leftmost parameters of a closure.

Example: closure.curry(value1) fixes value1 for the first parameter.
rcurry(): Fixes the rightmost parameters of a closure.

Example: closure.rcurry(valueN) fixes valueN for the last parameter.
ncurry(): Fixes parameters at a specific index in the closure.

Example: closure.ncurry(index, value) fixes the parameter at the given index.
These methods simplify repeated calls by pre-filling some arguments, improving code readability and maintainability.

Metaprogramming

In simple terms metaprogramming refers to writing code that can create, modify, generate and analyze other programs.It accepts other codes as its data and do some operations with it.

A best example for metaprogamming is the eval function in JavaScript, which accepts a string of JavaScript code and executes it.

Metaprograms are frequently used in everyday applications. For instance, integrated development environments (IDEs) like Visual Studio Code and IntelliJ IDEA use metaprogramming techniques to analyze code for syntax or compile-time errors even before the code is executed. The IDEs essentially act as programs that process and check the user's code for errors before runtime.

Metaprogramming in Groovy

Groovy supports two types of metaprogramming:

Runtime Metaprogramming:

Runtime metaprogramming in Groovy allows us to modify or extend the behaviour of classes and objects dynamically at runtime.

In Groovy, the invokeMethod() is a special method available in Groovy objects that is triggered when an undefined method is called on an object. By overriding invokeMethod(), we can customize how undefined method calls are handled.

Additionally, Groovy provides getProperty() and setProperty() methods. These methods intercept operations related to getting or setting properties in a class, allowing you to implement custom logic, such as validation, before retrieving or modifying property values.

class User{
    def name
    def age
    def email

    void setProperty(String name, Object value){
        if (value == null){
            value = ""
        }
        this.@"$name" = value.toString()
    }

    void print(){
        println "Name : ${name}, age : ${age}, email : ${email}"
    }
}

User user = new User()

user.name = "arun"
user.age = 2
user.email = null

user.print()

Output

Name : arun, age : 2, email :

Command Chains

Command chains in Groovy offer a concise and expressive way to call methods without using parentheses or dots (.) between method calls. This feature can make your code more readable, especially when you want to write more fluid and natural-looking expressions.

A command chain lets you call methods as if you were writing a sentence. Let’s look at an example:

class Car {
    def start() {
        println "Car started"
        return this
    }

    def drive() {
        println "Driving"
        return this
    }

    def stop() {
        println "Car stopped"
        return this
    }
}

def car = new Car()
car start drive stop

Output

Car started
Driving
Car stopped

In the above example, car start drive stop demonstrates a command chain where methods are called in sequence. Each method returns this, allowing the next method in the chain to be called on the same Car object.

In this blog, we explored various features of Groovy, from its metaprogramming capabilities and dynamic method handling to expressive features like command chains and delegation strategies. Groovy's ability to enhance code readability and flexibility through dynamic behaviour makes it a powerful tool for developers. By understanding and leveraging these features, you can write more intuitive and maintainable code.

If you have any questions, suggestions, or additional insights about Groovy or any other programming topics, please share your feedback in the comments below ?.

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