What Languages Are Used in Android App Development? Choosing Between Kotlin and Java

When you set out to start Android app development, the first thing you must decide is "which programming language to write in." Android development today is dominated by two languages, Kotlin and Java, and there is also the option of cross-platform development. This article organizes the languages used in Android app development and then explains, by purpose, how to choose between the mainstream Kotlin and Java in an easy-to-understand way.

Main Languages Used in Android App Development

There is more than one way to develop an Android app. First, let's grasp the overall picture of which languages are used. They broadly split into two streams: "Android native development" and "cross-platform development."

The Leads in Native Development: Kotlin and Java

When developing an Android-only app (a native app), the central languages are Kotlin and Java. Both are officially supported by Google, and you develop using the integrated development environment (IDE) called Android Studio. Java was long the standard language originally, but in 2017 Google adopted Kotlin as an official language, and in 2019 it announced a "Kotlin-first" policy. In new development today, Kotlin has become the mainstream.

Languages Used in Cross-Platform Development

If you "want to build an app that runs on both Android and iPhone from a single codebase," cross-platform development is an option. Representative examples include Flutter, developed by Google (its language is Dart), and React Native, developed by Meta (its language is JavaScript/TypeScript).

• Flutter (Dart): Covers both Android and iOS from one codebase. Easy to build UI, with fast rendering
• React Native (JavaScript): Lets you leverage web-development knowledge. Good fit with existing web engineers
• Unity (C#): Centered on game development. The choice if you want to build 3D or 2D game apps

However, if you "want to fully use Android's features" or "want to learn one OS in depth first," native development (Kotlin/Java) is the basis. From here, let's look in detail at how to choose between the mainstream Kotlin and Java.

What Is Kotlin? The Mainstream Language for Android Development Today

Kotlin is a programming language developed by JetBrains. While maintaining 100% compatibility with Java, it is designed to be written more concisely and safely, and it has become the de facto standard language in Android development today.

Advantages of Kotlin

• Concise to write: You can write the same processing with less code than Java, and readability is high
• Null safety: The language mechanism makes it easy to prevent Null (no value) errors, a common cause of app crashes
• Recommended by Google: New APIs, sample code, and official documentation are provided on a Kotlin-first basis
• Can coexist with Java: It can be mixed with existing Java code, so gradual migration is also possible

Disadvantages of Kotlin

Because it is a relatively new language, the accumulated volume of information and older explanatory articles is smaller than for Java. Even so, learning materials have rapidly expanded in recent years, so it is unlikely to be a major obstacle for those learning from now on.

What Is Java? The Standard Language with History and Track Record

Java is a long-established language that appeared in 1995 and was used as the standard language for a long time from the early days of Android. Many Android apps written in Java still run today, and its strengths are its legacy assets and the abundance of information.

Advantages of Java

• Abundant information and materials: Because it has been used for many years, books, explanatory articles, and troubleshooting tips have accumulated enormously
• High versatility: Beyond Android, Java is widely used in areas such as web apps and server-side development
• Affinity with legacy assets: Maintaining and modifying apps previously built in Java requires Java knowledge

Disadvantages of Java

Compared with Kotlin, the same processing tends to be more verbose to write. Also, because the mechanism for preventing Null-related errors is weak at the language level, you need to write carefully. The fact that Google's latest samples are centered on Kotlin is also a factor that can make information feel harder to find for new learners.

Comparing the Differences Between Kotlin and Java

The two are compatible, so "you can build Android apps with either," but they differ in writing style and design philosophy. The main differences can be organized as follows.

• Code volume: Kotlin is concise; Java tends to be verbose
• Null safety: Kotlin addresses it in the language spec; Java relies on the developer's caution
• Information volume: Java has abundant accumulation from long use; Kotlin is newer but rapidly increasing
• Google's policy: Recommends Kotlin. New development assumes Kotlin
• Ease of learning: For newcomers, Kotlin is simple and less likely to cause frustration

[By Purpose] How to Choose Between Kotlin and Java

In conclusion, if you are learning Android development from now on, Kotlin is the first choice. However, depending on the situation, Java may be more suitable. Let's organize the choice by purpose.

Learning Newly from Now On -> Kotlin

If you are starting Android development newly, there is no problem choosing Kotlin without hesitation. Because Google recommends it and new information is provided on a Kotlin-first basis, the knowledge you learn applies directly to the latest development. Its simple syntax, which makes it less likely for beginners to stumble, also makes it excellent as a first language.

Maintaining/Modifying Existing Java Apps -> Java

If you are taking over an app already built in Java, or your team operates in Java, you need Java knowledge. It is realistic to align with the existing on-site code, and there is no need to forcibly migrate to Kotlin.

If You Already Know Java -> Either Is Fine (Kotlin Recommended)

If you have Java experience, you can continue developing in Java by leveraging that knowledge, and migrating to Kotlin is also easy. Because Kotlin can be learned on the premise of Java knowledge, the hurdle to acquire it is low. In the long run, shifting toward Kotlin is a choice that also aligns with Google's policy.

Conclusion: Kotlin for New Development, Java for Maintenance as the Basis

The languages used in Android app development are mainly Kotlin and Java for native development, and if you aim to cover both OSes, there are also options such as Flutter (Dart) and React Native (JavaScript). The basic framing is: for native development, Kotlin (recommended by Google) is the first choice when learning from now on, and Java when handling existing Java assets.

You can start developing with either language for free in Android Studio. First, clarify your purpose (new development or modifying an existing app) and start building from a small app in the language suited to it.