Kotlin String - toString() Function

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The Kotlin string toString() function is used in kotlin when we override the "toString()" method in a class. It helps us to provide the custom string representation of object of that class.

When to use open override fun toString()

There are the following use cases of this function −

• Customize Object Description: Overriding toString() is useful when we want object of a class to return a meaningful representation.
• Inheritance Support: We need to mark the toString() class as open. If you want the subclass to inherit the string representation of the parent class.

Syntax

Following is the syntax of the Kotlin string toString() function −

open override fun toString(): String

Syntax and Usage

• open: This keyword helps the subclass to override the toString() function. A function cannot be overridden without the "open" keyword.
• override: This keyword helps to specify that the function is overriding a method from the parent class.

Parameters

This function does not accepts any parameters.

Return value

This function returns a string.

Example 1: Default Behaviour vs. Overridden Behaviour

Let us use the default toString() function in Kotlin −

class Example
fun main() {
   val example = Example()
   println(example.toString())
}

Output

If you do not override the toString() function, it will return the class name and the hash code of the object −

Example@3941a79c

Here, let's use the overridden toString() function −

class Example(val name: String, val age: Int, val city: String) {
    // Overriding the toString() method
    override fun toString(): String {
        return "Person(name='$name', age=$age, city='$city')"
    }
}

fun main() {
    val person = Example("Aman", 25, "Hyderabad")
    println(person.toString()) 

    // `toString()` is called implicitly when printing objects
    println(person)
}

Output

If we use overridden toString() Provides meaningful details about the object, making the output human-readable.

Person(name='Aman', age=25, city='Hyderabad')
Person(name='Aman', age=25, city='Hyderabad')

Example 2: Custom implementation of toString()

In this example, we create two classes overriding the class using the toString() function, displaying the details of both classes.

open class Animal(val name: String, val species: String) {
   open override fun toString(): String {
      return "Animal(name='$name', species='$species')"
   }
}

class Dog(name: String, species: String, val breed: String) : 
Animal(name, species) {
   override fun toString(): String {
      return "Dog(name='$name', species='$species', breed='$breed')"
   }
}

fun main() {
   val animal = Animal("Lion", "Mammal")
   println(animal.toString())

   val dog = Dog("Buddy", "Canine", "Golden Retriever")
   println(dog.toString())
}

Output

Following is the output −

Animal(name='Lion', species='Mammal')
Dog(name='Buddy', species='Canine', breed='Golden Retriever')