What keyword is used when a child derived class want to access or call function or properties of its parent base )? Kotlin?

Inheritance can be defined as the process where one class acquires the members (methods and properties) of another class. With the use of inheritance the information is made manageable in a hierarchical order.

Table of Contents Show

Overriding Methods
Overriding Properties
Derived Class Initialization Order
Access Super Class Members
Overriding rules
How do you access the variable of a parent class?
How do you use outer class variables in inner class Kotlin?
How do you access the variables of an extended class?
How do I use Kotlin inheritance?
How do you access the parent class members from the subclass?
Can child class access instance variables of parent class?
How do you access the variable of an outer class from an inner class?
Can inner class use variables from outer class?
How do I access inner class Kotlin?
How do you access an inherited class from base class?

A class which inherits the members of other class is known as subclass (derived class or child class) and the class whose members are being inherited is known as superclass (base class or parent class).

Inheritance is one of the key features of object-oriented programming which allows user to create a new class from an existing class. Inheritance we can inherit all the features from the base class and can have additional features of its own as well.

All classes in Kotlin have a common superclass called Any, which is the default superclass for a class with no supertypes declared:

class Example // Implicitly inherits from Any

Kotlin superclass Any has three methods: equals(), hashCode(), and toString(). Thus, these methods are defined for all Kotlin classes.

Everything in Kotlin is by default final, hence, we need to use the keyword open in front of the class declaration to make it inheritable for other classes. Kotlin uses operator ":" to inherit a class.

Example:

Take a look at the following example of inheritance.

open class ABC { fun think () { println("Hey!! i am thiking ") } } class BCD: ABC(){ // inheritence happend using default constructor } fun main(args: Array<String>) { var a = BCD() a.think() }

When you run the above Kotlin program, it will generate the following output:

Hey!! i am thiking

Overriding Methods

Now, what if we want to override the think() method in the child class. Then, we need to consider the following example where we are creating two classes and override one of its function into the child class.

open class ABC { open fun think () { println("Hey!! i am thinking ") } } class BCD: ABC() { // inheritance happens using default constructor override fun think() { println("I am from Child") } } fun main(args: Array<String>) { var a = BCD() a.think() }

When you run the above Kotlin program, it will generate the following output:

I am from Child

A member marked with keyword override is itself open, so it may be overridden in subclasses. If you want to prohibit re-overriding it then you must make it final as follows:

class BCD: ABC() { final override fun think() { println("I am from Child") } }

Overriding Properties

The overriding mechanism works on properties in the same way that it does on methods. Properties declared on a superclass that are then redeclared on a derived class must be prefaced with the keyword override, and they must have a compatible type.

open class ABC { open val count: Int = 0 open fun think () { println("Hey!! i am thinking ") } } class BCD: ABC() { override val count: Int init{ count = 100 } override fun think() { println("I am from Child") } fun displayCount(){ println("Count value is $count") } } fun main(args: Array<String>) { var a = BCD() a.displayCount() }

When you run the above Kotlin program, it will generate the following output:

Count value is 100

You can also override a val property with a var property, but not vice versa. This is allowed because a val property essentially declares a get method, and overriding it as a var additionally declares a set method in the derived class.

We can also can use the override keyword as part of the property declaration in a primary constructor. Following example makes the use of primary constructor to override count property, which will take default value as 400 in case we do not pass any value to the constructor:

open class ABC { open val count: Int = 0 open fun think () { println("Hey!! i am thinking ") } } class BCD(override val count: Int = 400): ABC() { override fun think() { println("I am from Child") } fun displayCount(){ println("Count value is $count") } } fun main(args: Array<String>) { var a = BCD(200) var b = BCD() a.displayCount() b.displayCount() }

When you run the above Kotlin program, it will generate the following output:

Count value is 200 Count value is 400

Derived Class Initialization Order

When we create an object of a derived class then constructor initialization starts from the base class. Which means first of all base class properties will be initialized, after that any derived class instructor will be called and same applies to any further derived classes.

This means that when the base class constructor is executed, the properties declared or overridden in the derived class have not yet been initialized.

open class Base { init{ println("I am in Base class") } } open class Child: Base() { init{ println("I am in Child class") } } class GrandChild: Child() { init{ println("I am in Grand Child class") } } fun main(args: Array<String>) { var a = GrandChild() }

When you run the above Kotlin program, it will generate the following output:

I am in Base class I am in Child class I am in Grand Child class

Access Super Class Members

Code in a derived class can call its superclass functions and properties directly using the super keyword:

open class Base() { open val name:String init{ name = "Base" } open fun displayName(){ println("I am in " + this.name) } } class Child(): Base() { override fun displayName(){ super.displayName() println("I am in " + super.name) } } fun main(args: Array<String>) { var a = Child() a.displayName() }

When you run the above Kotlin program, it will generate the following output:

I am in Base I am in Base

Overriding rules

If a child class inherits multiple implementations of the same member from its immediate superclasses, then it must override this member and provide its own implementation.

This is different from a child class which inherits members from a single parent, in such case case it is not mandatory for the child class to provide the implementation of all the open members.

open class Rectangle { open fun draw() { /* ... */ } } interface Polygon { fun draw() { /* ... */ } // interface members are 'open' by default } class Square() : Rectangle(), Polygon { // The compiler requires draw() to be overridden: override fun draw() { super<Rectangle>.draw() // call to Rectangle.draw() super<Polygon>.draw() // call to Polygon.draw() } }

It's fine to inherit from both Rectangle and Polygon, but both of them have their implementations of draw() method, so you need to override draw()in Square and provide a separate implementation for it to eliminate the ambiguity.

How To Use Variables From Parent Class In Kotlin With Code Examples

In this post, we will examine how to solve the How To Use Variables From Parent Class In Kotlin problem using examples from the programming language.

//add open to the inheirted variable open class A{ open var x=5 } class B:A(){ override var x=2*super.x }

We were able to fix the How To Use Variables From Parent Class In Kotlin problemcode by looking at a number of different examples.

How do you access the variable of a parent class?

Use of super with variables. This scenario occurs when a derived class and base class has the same data members.
Use of super with methods. This is used when we want to call the parent class method.
Use of super with constructors. The super keyword can also be used to access the parent class constructor.

How do you use outer class variables in inner class Kotlin?

Kotlin Inner Class Example

class outerClass{
private var name: String = "Ashu"
inner class innerClass{
var description: String = "code inside inner class"
private var id: Int = 101.
fun foo(){
println("name is ${name}") // access the outer class member even private.
println("Id is ${id}")

How do you access the variables of an extended class?

If you have a member in the subclass with the same name as the superclass, you can use super. var to access the superclass variable.

You don't need the super keyword. – mre.
That's right.
You would only need the super keyword if the field was hidden by a field in the subclass.
Also right 🙂 .

How do I use Kotlin inheritance?

Everything in Kotlin is by default final, hence, we need to use the keyword open in front of the class declaration to make it inheritable for other classes. Kotlin uses operator ":" to inherit a class.

How do you access the parent class members from the subclass?

Accessing Parent Class Functions This is really simple, you just have to call the constructor of parent class inside the constructor of child class and then the object of a child class can access the methods and attributes of the parent class. # how parent constructors are called.02-Jul-2020

Can child class access instance variables of parent class?

You inherit the following from the parent class. This means, the child class has all of the public methods that the parent class has. It has all of the instance variables. The only unusual aspect is that, within child class method definitions, you can't directly access parent class instance variables.

How do you access the variable of an outer class from an inner class?

Since inner classes are members of the outer class, you can apply any access modifiers like private , protected to your inner class which is not possible in normal classes. Since the nested class is a member of its enclosing outer class, you can use the dot ( . ) notation to access the nested class and its members.

Can inner class use variables from outer class?

Method Local inner classes can't use a local variable of the outer method until that local variable is not declared as final. For example, the following code generates a compiler error.24-Feb-2022

How do I access inner class Kotlin?

In Kotlin, to access the member function of nested class, we need to create the object for nested class and call the member function using it.05-Oct-2021

How do you access an inherited class from base class?

To access an element of a base class from an inherited class, you need to use the base keyword. The base keyword is used in inherited classes in the following cases: when from the constructor of a derived class you need to call the constructor of the base class.20-Mar-2020