Kotlin Getting Started Notes (6) Interface and Function Visibility Modifiers

Preface: This tutorial is best learned on the basis of JAVA

1. Interface

Kotlin's interface is almost identical to Java's

Define an interface:

interface Study{
    fun readBooks()
    fun doHomework()
}

Implement this interface with Student:

class Student(name : String , age : Int) :  Study {
    override fun readBooks() {
        println(name + " is reading.")
    }
    override fun doHomework(){
        println(name + " is doing homework.")
    }
}

Those who are familiar with Java must specify that Java inherits from extends   and implements interfaces from implements   , while Kotlin uses : (colon) uniformly .

Now we can write the following code in the main() function to call the functions in these two interfaces

fun main() {
    val student = Student("Jack",19)
    doStudy(student)
}
fun doStudy(study : Study) {
    study.readBooks()
    study.doHomework()
}

But Kotlin also adds a feature:

        Allows default implementations for functions defined in interfaces.

Not much to say, the code:

interface Study {
    fun readBooks()
    fun doHomework() {
        println("do homework default implementation.")
    }
}

 At this time, you will find that the Student will only be required to implement the readBooks function.

Second, the visibility modifier of the function

Default modifiers:

               Java :  default

               Kotlin : public

Kotlin abandons the default in Java and introduces a new concept: internal , which means that it is only visible to classes in the same module. protected is also different in Java and Kotlin, as shown in the following table:

Java and Kotlin function visibility modifier comparison table

Modifier	Java	Kotlin
public	All classes are visible	All classes are visible (default)
private	The current class is visible	The current class is visible
protected	The current class, subclasses, and classes under the same package path are visible	The current class and subclasses are visible
default	Classes under the same package path are visible (default)	none
internal	none	Classes in the same module are visible

If you like this series, please give it a thumbs up! Thanks for watching!

reference:

        "The First Line of Code Android (Third Edition)" --- Guo Lin