February 9, 2023

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Kotlin vs. Java: All-purpose Makes use of and Android Apps

11 min read

It’s true that Java misplaced the Android battle to Kotlin, which is now Google’s most popular language and due to this fact higher suited to new cellular apps. However each Kotlin and Java provide many strengths as general-purpose languages, and it’s necessary for builders to know the language variations, for functions similar to migrating from Java to Kotlin. On this article, we’ll break down Kotlin’s and Java’s variations and similarities so you may make knowledgeable selections and transfer seamlessly between the 2.

Are Kotlin and Java Comparable?

Certainly, the 2 languages have loads in frequent from a high-level perspective. Each Kotlin and Java run on the Java Digital Machine (JVM) as a substitute of constructing on to native code. And the 2 languages can name into one another simply: You possibly can name Java code from Kotlin and Kotlin code from Java. Java can be utilized in server-side functions, databases, internet front-end functions, embedded techniques and enterprise functions, cellular, and extra. Kotlin is equally versatile: It targets the JVM , Android, JavaScript, and Kotlin/Native, and will also be used for server-side, internet, and desktop growth.

Java is a way more mature language than Kotlin, with its first launch in 1996. Although Kotlin 1.0 was launched a lot later, in 2016, Kotlin shortly turned the official most popular language for Android growth in 2019. Exterior of Android, nevertheless, there isn’t any advice to interchange Java with Kotlin.

Yr

Java

Kotlin

1995–2006

JDK Beta, JDK 1.0, JDK 1.1, J2SE 1.2, J2SE 1.3, J2SE 1.4, J2SE 5.0, Java SE 6

N/A

2007

Venture Loom first commit

N/A

2010

N/A

Kotlin growth began

2011

Java SE 7

Kotlin undertaking introduced

2012

N/A

Kotlin open sourced

2014

Java SE 8 (LTS)

N/A

2016

N/A

Kotlin 1.0

2017

Java SE 9

Kotlin 1.2; Kotlin help for Android introduced

2018

Java SE 10, Java SE 11 (LTS)

Kotlin 1.3 (coroutines)

2019

Java SE 12, Java SE 13

Kotlin 1.4 (interoperability for Goal-C and Swift); Kotlin introduced as Google’s most popular language for builders

2020

Java SE 14, Java SE 15

N/A

2021

Java SE 16, Java SE 17 (LTS)

Kotlin 1.5, Kotlin 1.6

2022

Java SE 18, JDK 19 EAB (Venture Loom)

Kotlin 1.7 (alpha model of Kotlin K2 compiler)

Kotlin vs. Java: Efficiency and Reminiscence

Earlier than detailing Kotlin’s and Java’s options, we’ll look at their efficiency and reminiscence consumption as these elements are usually necessary concerns for builders and purchasers.

Kotlin, Java, and the opposite JVM languages, though not equal, are pretty related when it comes to efficiency, no less than when in comparison with languages in different compiler households like GCC or Clang. The JVM was initially designed to focus on embedded techniques with restricted assets within the Nineties. The associated environmental necessities led to 2 essential constraints:

  • Easy JVM bytecode: The present model of JVM, wherein each Kotlin and Java are compiled, has solely 205 directions. Compared, a contemporary x64 processor can simply help over 6,000 encoded directions, relying on the counting methodology.
  • Runtime (versus compile-time) operations: The multiplatform strategy (“Write once and run anywhere”) encourages runtime (as a substitute of compile-time) optimizations. In different phrases, the JVM interprets the majority of its bytecode into directions at runtime. Nonetheless, to enhance efficiency, it’s possible you’ll use open-source implementations of the JVM, similar to HotSpot, which pre-compiles the bytecode to run sooner by the interpreter.

With related compilation processes and runtime environments, Kotlin and Java have solely minor efficiency variations ensuing from their distinct options. For instance:

  • Kotlin’s inline capabilities keep away from a perform name, bettering efficiency, whereas Java invokes extra overhead reminiscence.
  • Kotlin’s higher-order capabilities keep away from Java lambda’s particular name to InvokeDynamic, bettering efficiency.
  • Kotlin’s generated bytecode comprises assertions for nullity checks when utilizing exterior dependencies, slowing efficiency in comparison with Java.

Now let’s flip to reminiscence. It’s true in idea that using objects for base sorts (i.e., Kotlin’s implementation) requires extra allocation than primitive information sorts (i.e., Java’s implementation). Nonetheless, in observe, Java’s bytecode makes use of autoboxing and unboxing calls to work with objects, which might add computational overhead when utilized in extra. For instance, Java’s String.format method solely takes objects as enter, so formatting a Java int will field it in an Integer object earlier than the decision to String.format.

On the entire, there are not any important Java and Kotlin variations associated to efficiency and reminiscence. It’s possible you’ll look at online benchmarks which present minor variations in micro-benchmarks, however these can’t be generalized to the dimensions of a full manufacturing software.

Distinctive Function Comparability

Kotlin and Java have core similarities, however every language affords completely different, distinctive options. Since Kotlin turned Google’s most popular language for Android growth, I’ve discovered extension capabilities and express nullability to be essentially the most helpful options. Alternatively, when utilizing Kotlin, the Java options that I miss essentially the most are the protected key phrase and the ternary operator.

From left to right are shown a white Variable oval, an equals sign, a green First Expression box, a question mark, a dark blue Second Expression box, a colon, and a light blue Third Expression box. The First Expression box has two arrows: one labeled “Is True” points to the Second Expression box, and the second labeled “Is False” points to the Third Expression box. Second Expression and Third Expression each have their own Return Value arrow pointing to the Variable oval.
The Ternary Operator

Let’s look at a extra detailed breakdown of options out there in Kotlin versus Java. It’s possible you’ll observe together with my examples utilizing the Kotlin Playground or a Java compiler for a extra hands-on studying strategy.

Function

Kotlin

Java

Description

Extension capabilities

Sure

No

Means that you can lengthen a category or an interface with new functionalities similar to added properties or strategies with out having to create a brand new class:

class Instance 

// extension perform declaration
enjoyable Instance.printHelloWorld()  println("Good day World!") 

// extension perform utilization
Instance().printHelloWorld()

Sensible casts

Sure

No

Retains observe of circumstances inside if statements, secure casting mechanically:

enjoyable instance(a: Any) 
  if (a is String) 
    println(a.size) // automated forged to String
  

Kotlin additionally supplies secure and unsafe forged operators:

// unsafe "as" forged throws exceptions
val a: String = b as String
// secure "as?" forged returns null on failure
val c: String? = d as? String

Inline capabilities

Sure

No

Reduces overhead reminiscence prices and improves velocity by inlining perform code (copying it to the decision web site): inline enjoyable instance().

Native help for delegation

Sure

No

Helps the delegation design pattern natively with using the by key phrase: class Derived(b: Base) : Base by b.

Kind aliases

Sure

No

Offers shortened or customized names for present sorts, together with capabilities and internal or nested courses: typealias ShortName = LongNameExistingType.

Non-private fields

No

Sure

Affords protected and default (also referred to as package-private) modifiers, along with public and personal modifiers. Java has all 4 access modifiers, whereas Kotlin is lacking protected and the default modifier.

Ternary operator

No

Sure

Replaces an if/else assertion with easier and extra readable code:

if (firstExpression)  // if/else
  variable = secondExpression;
 else 
  variable = thirdExpression;


// ternary operator
variable = (firstExpression) ? secondExpression : thirdExpression;

Implicit widening conversions

No

Sure

Permits for automated conversion from a smaller information kind to a bigger information kind:

int i = 10;
lengthy l = i; // first widening conversion: int to lengthy
float f = l; // second widening conversion: lengthy to drift

Checked exceptions

No

Sure

Requires, at compile time, a way to catch exceptions with the throws key phrase or handles exceptions with a try-catch block.

Word: Checked exceptions have been supposed to encourage builders to design strong software program. Nonetheless, they’ll create boilerplate code, make refactoring tough, and result in poor error dealing with when misused. Whether or not this characteristic is a professional or con is determined by developer choice.

There may be one matter I’ve deliberately excluded from this desk: null security in Kotlin versus Java. This matter warrants a extra detailed Kotlin to Java comparability.

Kotlin vs. Java: Null Security

For my part, non-nullability is likely one of the biggest Kotlin options. This characteristic saves time as a result of builders don’t should deal with NullPointerExceptions (that are RuntimeExceptions).

In Java, by default, you’ll be able to assign a null worth to any variable:

String x = null;
// Operating this code throws a NullPointerException
attempt 
    System.out.println("First character: " + x.charAt(0));
 catch (NullPointerException e) 
    System.out.println("NullPointerException thrown!");

In Kotlin, alternatively, now we have two choices, making a variable nullable or non-nullable:

var nonNullableNumber: Int = 1

// This line throws a compile-time error as a result of you'll be able to't assign a null worth
nonNullableNumber = null

var nullableNumber: Int? = 2

// This line doesn't throw an error since we used a nullable variable
nullableNumber = null

I exploit non-nullable variables by default, and decrease using nullable variables for greatest practices; these Kotlin versus Java examples are supposed to display variations within the languages. Kotlin novices ought to keep away from the entice of setting variables to be nullable with out a objective (this could additionally occur whenever you convert Java code to Kotlin).

Nonetheless, there are a number of circumstances the place you’d use nullable variables in Kotlin:

State of affairs

Instance

You’re looking for an merchandise in a listing that’s not there (often when coping with the information layer).

val record: Listing<Int> = listOf(1,2,3)
val searchResultItem = record.firstOrNull  it == 0 
searchResultItem?.let  
  // Merchandise discovered, do one thing 
 ?: run  
  // Merchandise not discovered, do one thing

You wish to initialize a variable throughout runtime, utilizing lateinit.

lateinit var textual content: String

enjoyable runtimeFunction()  // e.g., Android onCreate
  textual content = "First textual content set"
  // After this, the variable can be utilized

I used to be responsible of overusing lateinit variables after I first received began with Kotlin. Ultimately, I finished utilizing them nearly utterly, besides when defining view bindings and variable injections in Android:

@Inject // With the Hilt library, that is initialized mechanically
lateinit var supervisor: SomeManager

lateinit var viewBinding: ViewBinding

enjoyable onCreate()  // i.e., Android onCreate

  binding = ActivityMainBinding.inflate(layoutInflater, parentView, true)
  // ...

On the entire, null security in Kotlin supplies added flexibility and an improved developer expertise in comparison with Java.

Shared Function Variations: Transferring Between Java and Kotlin

Whereas every language has distinctive options, Kotlin and Java share many options too, and it’s essential to know their peculiarities with a view to transition between the 2 languages. Let’s look at 4 frequent ideas that function in another way in Kotlin and Java:

Function

Java

Kotlin

Knowledge switch objects (DTOs)

Java data, which maintain details about information or state and embody toString, equals, and hashCode strategies by default, have been out there since Java SE 15:

public document Worker(
  int id,
  String firstName,
  String lastName
) 

Kotlin information courses perform equally to Java data, with toString, equals, and copy strategies out there:

information class Worker(
  val id: Int,
  val firstName: String,
  val lastName: String
) 

Lambda expressions

Java lambda expressions (out there since Java 8) observe a easy parameter -> expression syntax, with parentheses used for a number of parameters: (parameter1, parameter2) -> code :

ArrayList<Integer> ints =
  new ArrayList<>();
ints.add(5);
ints.add(9);
ints.forEach( (i) ->
   System.out.println(i);  );

Kotlin lambda expressions observe the syntax parameter1, parameter2 -> code and are at all times surrounded by curly braces:

var p: Listing<String> =
  listOf("firstPhrase", "secondPhrase")
val isShorter =  s1: String,
  s2: String -> s1.size < s2.size 
println(isShorter(p.first(), p.final()))

Concurrency

Java threads make concurrency attainable, and the java.util.concurrency package deal permits for simple multithreading by its utility courses. The Executor and ExecutorService classes are particularly useful for concurrency. (Project Loom additionally affords light-weight threads.)

Kotlin coroutines, from the kotlinx.coroutines library, facilitate concurrency and embody a separate library department for multithreading. Kotlin 1.7.20’s new memory manager reduces earlier limitations on concurrency and multithreading for builders shifting between iOS and Android.

Static conduct in courses

Java static members facilitate the sharing of code amongst class situations and be certain that solely a single copy of an merchandise is created. The static key phrase might be utilized to variables, capabilities, blocks, and extra:

class Instance 
    static void f() /*...*/
 

Kotlin companion objects provide static conduct in courses, however the syntax is just not as easy:

class Instance 
    companion object 
        enjoyable f() /*...*/
    

After all, Kotlin and Java even have various syntaxes. Discussing each syntax distinction is past our scope, however a consideration of loops ought to provide you with an thought of the general state of affairs:

Loop Kind

Java

Kotlin

for, utilizing in

for (int i=0; i<=5; i++) 
  System.out.println("printed 6 occasions");
for (i in 0..5) 
  println("printed 6 occasions")

for, utilizing till

for (int i=0; i<5; i++) 
  System.out.println("printed 5 occasions");
for (i in 0 till 5) 
  println("printed 5 occasions")

forEach

Listing<String> record = Arrays.asList("first", "second");

for (String worth: record) 
  System.out.println(worth);
var record: Listing<String> =
  listOf("first", "second")

record.forEach 
  println(it)

whereas

int i = 5;
whereas (i > 0) 
  System.out.println("printed 5 occasions");
  i--;
var i = 5
whereas (i > 0) 
  println("printed 5 occasions")
  i--

An in-depth understanding of Kotlin options will help in transitions between Kotlin and Java.

Android Venture Planning: Further Issues

We’ve examined many necessary elements to consider when deciding between Kotlin and Java in a general-purpose context. Nonetheless, no Kotlin versus Java evaluation is full with out addressing the elephant within the room: Android. Are you making an Android software from scratch and questioning in the event you ought to use Java or Kotlin? Select Kotlin, Google’s most popular Android language, unquestionably.

Nonetheless, this query is moot for present Android functions. In my expertise throughout a variety of purchasers, the 2 extra necessary questions are: How are you treating tech debt? and How are you caring for your developer expertise (DX)?

So, how are you treating tech debt? In case your Android app is utilizing Java in 2022, your organization is probably going pushing for brand new options as a substitute of coping with tech debt. It’s comprehensible. The market is aggressive and calls for a quick turnaround cycle for app updates. However tech debt has a hidden impact: It causes elevated prices with every replace as a result of engineers should work round unstable code that’s difficult to refactor. Corporations can simply enter a endless cycle of tech debt and value. It could be price pausing and investing in long-term options, even when this implies large-scale code refactors or updating your codebase to make use of a contemporary language like Kotlin.

And the way are you caring for your builders by DX? Builders require help throughout all ranges of their careers:

  • Junior builders profit from correct assets.
  • Mid-level builders develop by alternatives to guide and educate.
  • Senior builders require the ability to architect and implement lovely code.

Consideration to DX for senior builders is very necessary since their experience trickles down and impacts all engineers. Senior builders like to study and experiment with the most recent applied sciences. Maintaining with newer tendencies and language releases will enable your workforce members to succeed in their biggest potential. That is necessary whatever the workforce’s language alternative, although completely different languages have various timelines: With younger languages like Kotlin, an engineer engaged on legacy code can fall behind tendencies in lower than one yr; with mature languages like Java, it’s going to take longer.

Kotlin and Java: Two Highly effective Languages

Whereas Java has a variety of functions, Kotlin has undeniably stolen its thunder as the popular language for the event of latest Android apps. Google has put all of its efforts into Kotlin, and its new applied sciences are Kotlin-first. Builders of present apps would possibly take into account integrating Kotlin into any new code—IntelliJ comes with an automated Java to Kotlin tool—and may look at elements that attain past our preliminary query of language alternative.


The editorial workforce of the Toptal Engineering Weblog extends its gratitude to Thomas Wuillemin for reviewing the code samples and different technical content material introduced on this article.

Additional Studying on the Toptal Engineering Weblog:

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