Clojure Functional Programming & JVM Backend Development · Pelajaran

Memanggil Java dari Clojure

Temukan cara memanggil metode Java, mengakses bidang, dan membuat instans objek langsung dari kode Clojure

Memanggil Java dari Clojure adalah pelajaran Clojure Functional Programming & JVM Backend Development gratis di CoddyKit. Ini adalah pelajaran 1 dari 4. Kamu bisa membaca pelajaran lengkapnya di bawah secara gratis — lalu praktikkan langsung di browser dengan editor kode bawaan dan tutor AI 24/7. Ini adalah bagian dari jalur belajar Clojure Functional Programming & JVM Backend Development, dan progresmu tersinkronisasi di web dan aplikasi CoddyKit. Kursus Clojure Functional Programming & JVM Backend Development mencakup 4 pelajaran total.

Bagian dari pelajaran ini belum diterjemahkan dan ditampilkan dalam bahasa Inggris.

Clojure & Java: Best Friends!

Clojure runs on the Java Virtual Machine (JVM), which means it can use all the amazing Java libraries directly! This is called Java Interop.

Access Java classes and methods.
Leverage the vast Java ecosystem.
Combine Clojure's power with Java's stability.

This lesson will show you how to call Java code from Clojure.

Creating Java Objects

To use a Java class, you often need to create an instance of it. In Clojure, you can do this using a special syntax.

Use (new ClassName args) or the shorthand (ClassName. args).
The . after the class name is a convenient way to call a constructor.

Example: (java.util.Date.) creates a new Date object.

Demo: New Date Object

Try creating a new java.util.Date object. It will represent the current date and time.

(ns my-app.core
  (:gen-class))

(defn -main
  "Creates and prints a new Java Date object."
  [& args]
  (let [current-date (java.util.Date.)]
    (println "Current date:" current-date)))

Calling Static Java Methods

Static methods belong to the class itself, not to a specific object instance. You can call them directly on the class.

Syntax: (ClassName/staticMethodName args)
The / separates the class name from the static method name.

Example: (java.lang.Math/random) calls the random static method of the Math class.

Demo: Math.random()

Let's get a random number using Java's Math/random static method. It returns a double between 0.0 (inclusive) and 1.0 (exclusive).

(ns my-app.core
  (:gen-class))

(defn -main
  "Generates and prints a random number using Java's Math/random."
  [& args]
  (let [rand-num (java.lang.Math/random)]
    (println "Random number:" rand-num)))

Calling Instance Java Methods

Once you have an object, you can call its instance methods. These methods operate on that specific object's data.

Syntax: (.methodName instance args) or (. instance methodName args).
The . before the method name indicates an instance method call.

Example: (.getTime my-date) calls the getTime method on the my-date object.

Demo: Date.getTime()

Create a Date object and then call its getTime() method. This method returns the number of milliseconds since January 1, 1970, 00:00:00 GMT.

(ns my-app.core
  (:gen-class))

(defn -main
  "Creates a Date object and calls its getTime() method."
  [& args]
  (let [current-date (java.util.Date.)
        time-in-millis (.getTime current-date)]
    (println "Current date:" current-date)
    (println "Milliseconds since epoch:" time-in-millis)))

Accessing Java Fields

Java objects can have fields (variables) that store data. You can access these fields directly from Clojure.

Syntax: (.-fieldName instance) for getting a field's value.
For static fields, use (.-staticFieldName ClassName).

Example: (.-out System) accesses the out static field of the System class, which is a PrintStream.

Demo: System.out Field

The java.lang.System class has a static field named out, which is a PrintStream object. We can access it to print to the console.

(ns my-app.core
  (:gen-class))

(defn -main
  "Accesses System.out and prints a message using its println method."
  [& args]
  (let [out-stream (.-out java.lang.System)]
    (.println out-stream "Hello from System.out!")))

Quick Check: Java Interop

You've learned how to interact with Java classes. Which Clojure expression uses the ClassName. shorthand to instantiate a java.io.File object for the path "myfile.txt"?

Recap: Java Interop Basics

Great job! You've learned the fundamentals of interacting with Java from Clojure:

Instantiate objects: Use (ClassName. args) or (new ClassName args).
Call static methods: Use (ClassName/staticMethodName args).
Call instance methods: Use (.methodName instance args) or (. instance methodName args).
Access fields: Use (.-fieldName instance).

This powerful capability allows you to leverage the entire Java ecosystem within your Clojure projects. Next, we'll explore implementing Java interfaces.

Pertanyaan yang Sering Diajukan

Apakah pelajaran “Memanggil Java dari Clojure” gratis?

Ya — teks lengkap “Memanggil Java dari Clojure” gratis dibaca di sini di web. Untuk praktiknya secara interaktif (editor kode bawaan dan tutor AI 24/7) dan buka sisa kursus Clojure Functional Programming & JVM Backend Development, upgrade ke CoddyKit PRO. Kursus Clojure Functional Programming & JVM Backend Development mencakup 4 pelajaran total.

Apa yang akan aku pelajari di “Memanggil Java dari Clojure”?

Temukan cara memanggil metode Java, mengakses bidang, dan membuat instans objek langsung dari kode Clojure Kamu berlatih Clojure Functional Programming & JVM Backend Development dengan kode praktik yang langsung kamu jalankan di browser, dan tutor AI 24/7 menjawab pertanyaanmu saat kamu mengerjakan pelajaran ini.

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