What types of constructors exist in Kotlin and how are they used in classes?

In Kotlin, there are two main types of constructors:

• Primary constructor — declared in the class header and initializes the main parameters of the class.
• Secondary constructors — declared inside the class body using the constructor keyword and can be used for additional initialization.

Example:

class User(val name: String, var age: Int) { // primary constructor
    constructor(name: String) : this(name, 0) { // secondary constructor
        println("User created with name $name and default age")
    }
}

The primary constructor is usually used for mandatory parameters, while the secondary is for creating objects with different sets of parameters.