Kotlin and Java are both programming languages that can be used for a variety of purposes, but they have some key differences, especially when it comes to Android app development.

Java is a mature and widely-used programming language that has been around for over two decades. It is known for its readability, reliability, and portability. Java is the primary language for developing Android apps and is supported by a large community of developers.

Kotlin, on the other hand, is a newer programming language that was first introduced in 2011. It is considered to be more expressive, concise, and safe than Java. Kotlin is fully compatible with Java and can run on the Java Virtual Machine (JVM). In 2017, Google announced that Kotlin is an officially supported language for Android development, making it a popular choice among Android developers.

In terms of all-purpose uses, Java is often used for building enterprise applications, web development, and big data. Java’s large and active community also leads to a vast number of libraries and frameworks that developers can use to speed up their development process.

Kotlin, on the other hand, is more often used for mobile app development, particularly for Android. It is also used for building back-end systems and server-side applications. Its concise and expressive nature make it a good choice for building complex applications with fewer lines of code.

In conclusion, both Kotlin and Java are powerful programming languages that can be used for a variety of purposes. However, Java is more widely used and has a larger community, while Kotlin is more popular among Android developers and is considered to be more expressive and safe. The choice of which one to use would depend on the specific requirements and goals of your project.