| Null Safety |
By default, all sorts of variables in Kotlin are non-nullable (that is, we can't assign null values to any variables or objects). Kotlin code will fail to build if we try to assign or return null values. If we absolutely want a null value for a variable, we can declare it as follows: value num: Int? = null |
NullPointerExceptions are a big source of annoyance for Java developers. Users can assign null to any variable, however, when accessing an object reference with a null value, a null pointer exception is thrown, which the user must manage. |
| Coroutines Support |
We can perform long-running expensive tasks in several threads in Kotlin, but we also have coroutines support, which halt execution at a given moment without blocking threads while doing long-running demanding operations. |
The corresponding thread in Java will be blocked anytime we launch a long-running network I/0 or CPU-intensive task. Android is a single-threaded operating system by default. Java allows you to create and execute numerous threads in the background, but managing them is a difficult operation. |
| Data Classes |
If we need to have data-holding classes in Kotlin, we may define a class with the keyword "data" in the class declaration, and the compiler will take care of everything, including constructing constructors, getter, and setter methods for various fields. |
Let's say we need a class in Java that only holds data and nothing else. Constructors, variables to store data, getter and setter methods, hashcode(), function toString(), and equals() functions are all required to be written explicitly by the developer. |
| Functional Programming |
Kotlin is procedural and functional programming (a programming paradigm where we aim to bind everything in functional units) language that has numerous useful features such as lambda expressions, operator overloading, higher-order functions, and lazy evaluation, among others. |
Java does not allow functional programming until Java 8, however it does support a subset of Java 8 features when developing Android apps. |
| Extension Functions |
Kotlin gives developers the ability to add new functionality to an existing class. By prefixing the name of a class to the name of the new function, we can build extended functions. |
In Java, we must create a new class and inherit the parent class if we want to enhance the functionality of an existing class. As a result, Java does not have any extension functions. |
| Data Type Inference |
We don't have to declare the type of each variable based on the assignment it will handle in Kotlin. We can specify explicitly if we want to. |
When declaring variables in Java, we must declare the type of each variable explicitly. |
| Smart Casting |
Smart casts in Kotlin will take care of these casting checks with the keyword "is-checks," which checks for immutable values and conducts implicit casting. |
We must examine the type of variables in Java and cast them appropriately for our operation. |
| Checked Exceptions |
We don't have checked exceptions in Kotlin. As a result, developers do not need to declare or catch exceptions, which has both benefits and drawbacks. |
We have checked exceptions support in Java, which enables developers to declare and catch exceptions, resulting in more robust code with better error handling. |
