Kotlin is better than Java in terms of syntax simplicity, reducing boilerplate code, supporting empty security, type inference and extension functions, and improving development efficiency; 2. The two are close to Spring ecological integration. Spring Boot officially supports Kotlin, but Java is more "native"; 3. The performance differences are extremely small, the JVM executes bytecode consistent, and the performance gap can be ignored in actual projects; 4. Java has obvious advantages in community, library support and recruitment, and Kotlin is catching up quickly, especially in emerging frameworks; 5. Kotlin coroutines provide a more concise asynchronous programming model compared to Java's CompletableFuture, which is suitable for high-concurrency I/O-intensive scenarios; Selection suggestions: If a new project and the team is willing to learn, choose Kotlin, maintain the legacy system or the team uses Java. Mainly, continue to use Java. Both can build efficient back-end services, which depends on the team's technology stack and business needs.

Java and Kotlin are both JVM languages widely used in modern backend development, and occupy an important position in enterprise-level services and Android development. With the rise of Kotlin, more and more teams have begun to choose it in new projects, but Java is still in the mainstream with its mature ecosystem. The following is a practical back-end development comparison of the two from multiple dimensions.

1. Syntax simplicity and development efficiency

Kotlin clearly won .

One of Kotlin's design goals is to reduce boilerplate code in Java, which makes back-end development more efficient and less error-making.

• Data class : Defining a simple DTO in Java may require writing getter , setter , toString , equals , hashCode , while Kotlin only requires one line:

   data class User(val id: Long, val name: String)

• Empty security : Kotlin handles null pointer problems during compilation period. The type system distinguishes between nullable and non-nullable types, reducing runtime crashes.

   var name: String = "Alice"
  var nickname: String? = null // Explicit declaration can be null

• Intelligent type inference : val list = listOf("a", "b") , no need to explicitly declare the type.
• Extended functions : You can add methods to the class without modifying it, which is very useful for tool classes and DSL construction.

In contrast, although Java has improved in newer versions (such as var and records ), the overall syntax is still verbose.

? Summary: Kotlin is more suitable for rapid development and reduce errors, especially in the API layer and service logic.

2. Integration with the Spring Ecosystem

The two are almost the same, but Kotlin's support is getting better and better .

Spring Boot is the de facto standard for Java backends, and it provides first-class support for Kotlin.

• The official Spring Boot template supports Kotlin.
• Kotlin's coroutines can be used with Spring WebFlux for responsive programming.
• When using Kotlin Spring Data JPA, the data class works well with the entity class.
• But note: When using @Configuration or @Bean , Kotlin's final default behavior may affect the CGLIB proxy, and skills such as open or using @JvmOverloads are required.

Java is still the most "native" choice, especially in large traditional enterprise projects, where all libraries and documents are built around Java.

?? Note: If your team is familiar with Java, it will take a certain learning cost to migrate to Kotlin, especially the usage habits of empty security and scoped functions ( apply , let , etc.).

3. Performance and runtime performance

The actual difference is minimal and the performance is almost flat .

Although Kotlin generates slightly more bytecode after compilation (such as synthesis methods and default parameter processing), in real backend services:

• The JVM executes bytecode, and both end up running on the JVM.
• JIT compilation optimization treats both equally.
• There was no significant difference in memory footprint, throughput, and GC performance.

In microbenchmarks, Java may be several percentage points faster in some extreme scenarios, but it is far less of an impact than code design, database optimization, and caching strategies.

? Actual project advice: Don't reject Kotlin due to performance concerns, unless you are doing high-frequency trading or extreme performance-sensitive systems.

4. Community, library support and team collaboration

Java has obvious advantages, and Kotlin is catching up .

• Library Compatibility : Kotlin is fully Java compatible and can call any Java library. But in turn, Java calls to Kotlin's advanced features (such as default parameters, coroutines) may require @JvmOverloads or wrappers.
• Documents and tutorials : Java has richer learning resources, especially in terms of enterprise architecture, security, monitoring, etc.
• Team Recruitment : There are far more Java developers than Kotlin, especially in small and medium-sized cities or traditional industries.
• Long-term maintenance : Java has strong support from Oracle and OpenJDK communities, and the version update is stable. Kotlin is driven by JetBrains and, while active, is still small in size.

However, in emerging technology stacks (such as Ktor, Micronaut, Quarkus), Kotlin's support is more natural, and the coroutine model is more suitable for asynchronous programming.

5. Coroutine vs. Thread Model

Kotlin coroutines are a major advantage of back-end asynchronous programming .

Java mainly relies on the thread pool CompletableFuture to implement asynchronously, and the code is easy to become complicated:

 CompleteFuture.supplyAsync(() -> fetchUser())
                 .thenApply(user -> enrichUser(user))
                 .thenAccept(System.out::println);

And Kotlin coroutines make asynchronous code look synchronous and easier to read:

 suspend fun processUser() {
    val user = fetchUser()
    val enriched = enrichUser(user)
    println(enriched)
}

With kotlinx.coroutines , lightweight concurrency can be easily achieved, especially suitable for I/O-intensive services (such as calling external APIs and database queries).

? Recommended scenarios: high concurrency, inter-microservice calls, event-driven architecture.

Summary: How to choose?

? Basically that's it. If you are starting a new backend project and the team is willing to learn, Kotlin is a more modern and efficient choice ; if you are maintaining large legacy systems or the team mainly uses Java, it is completely fine to continue using Java . Both can build high-performance, scalable back-end services, and the key is to rely on team and business needs.

The above is the detailed content of Java vs. Kotlin: A Comprehensive Backend Comparison. For more information, please follow other related articles on the PHP Chinese website!