Kotlin Interfaces

An interface is a type that defines a set of methods and properties that a class can implement. It provides a way to define a contract between the implementing class and the calling code. An interface can be thought of as a blueprint for a class, where the class must implement all the methods and properties defined in the interface.

Creating An Interface

This is how the basic syntax of an interface can be created:

interface Name {
  // Properties and functions go here in the body.
}

Example

In the following code example, an interface named MyListener is defined and a class named Name which inherits it:

fun main() {
  var myObject = Name()
  println(myObject.name)

  myObject.name ="XYZ"
  println(myObject.name)

  myObject.EmptyFn()
}

interface Mylistener {
  var name: String  // The normal properties are by default abstract in nature it cannot be given a body.

  fun jump() {
    print("World")
  } // The function's body shows that its `open` in nature.

  fun EmptyFn() // Methods are by default `open` and `public` in nature so it can give the body for the function or call it in other class and override it.
}

class Name : Mylistener {
  override var name: String = "Hello"

  override fun EmptyFn() {
    println("Override Text")
  }

  override fun jump() {} // Optional to override.
}

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In the code above, the Mylistener interface declares a property and two functions:

• name is a read-write property of type String.
• jump() is a function with a default implementation that prints the text "World".
• EmptyFn() is a function without a body.

The Name class implements the Mylistener interface and overrides its two functions and property. The name property is initialized to "Hello" and is made writable in the Name class. The EmptyFn() function is also overridden with a new implementation that prints the text "Override Text". The jump() function is optional to override but is done so here, so the print("World") in the interface will not run.

The output for the above code will be:

Hello
XYZ
Override Text

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