2. Difference between Java and Kotlin.

What Java has that Kotlin does not.

  • Kotlin doesn’t have checked exceptions: It means that you can’t use the word throws in a function to make sure that when someone use this function the exception will be checked by a try-catch block.
  • Primitive types: In Kotlin all are classes, including the primitive types.
  • Static members: Kotlin doesn’t have static methods.
  • Non-private fields: You can’t declare a field as non-private.
  • Wildcard-types: Kotlin doesn’t have wildcard types. The wildcard type (?) in Java is used to set any type as a parameter in a generic type.
  • Ternary-operator: Kotlin doesn’t have the ternary operator: a ? b : c

What Kotlin has that Java does not.

Here you have a list of properties that Kotlin has but Java does not. I’ll not explain them yet, but I’ll do when we see the syntax of properties.

  • Lambda expressions + Inline functions = performant custom control structures.
  • Extension functions.
  • Null-safety.
  • Smart casts.
  • String templates.
  • Primary constructors.
  • First-class delegation.
  • Type inference for variable and property types.
  • Declaration-site variance & Type projections.
  • Range expressions.
  • Operator overloading.
  • Companion objects.
  • Data classes.
  • Separate interfaces for read-only and mutable collections.

Here you have the list which redirect you to the topics:

https://kotlinlang.org/docs/reference/comparison-to-java.html

Issues of Java addressed in Kotlin.

  • Null references are controlled by the type system. Kotlin’s type system is aimed to avoid the danger of null references, also known in java like NullPointerException (NPE).
  • No raw types: Kotlin is designed to run calling code from Java in a natural way and Java can run calling code from Kotlin as well, using getters and setters in the right way, avoiding the keywords and with the safety of null references.
  • Arrays in Kotlin are invariant, that has get() and set() functions.
  • Kotlin has proper function types, as opposed to Java’s SAM-conversions: The functions in Kotlin are high levelled than Java.
  • Use-site variance without wildcards: It is very convenient to declare a type parameter T as out and avoid trouble with subtyping on the use site.
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