(13) Kotlin object expressions and object declarations

Source: Internet
Author: User
Tags anonymous
Kotlin Object expressions and object declarations

Kotlin uses object expressions and object declarations to implement an object that creates a class that makes minor changes to a class, and does not need to declare a new subclass. an object expression

An object that implements an anonymous inner class through an object expression is used in the parameters of the method:

Window.addmouselistener (Object:mouseadapter () {
    override fun mouseclicked (e:mouseevent) {
    Override Fun Mouseentered (e:mouseevent) {

Objects can inherit from a base class, or implement other interfaces:

Open Class A (x:int) {public
    open val y:int = x

interface B {...}

Val ab:a = object:a (1), B {
    override val y = +

If the superclass has a constructor, you must pass the parameter to it. Multiple hyper-types and interfaces can be separated by commas.

Object expressions allow you to get an object directly over the definition of a class:

Fun Main (args:array<string>) {
    val site = object {
        var name:string = "Rookie Tutorial"
        var url:string = "Www.run Oob.com "
    println (site.name)
    println (site.url)

Note that anonymous objects can be used as types that are declared only on local and private scopes. If you use an anonymous object as the return type of a public function or as a type of a public property, the actual type of the function or property is the super-type of the anonymous object declaration, or any if you do not declare any of the superclass types. Members added in the anonymous object will not be accessible.

Class C {
    //private function, so its return type is anonymous object type
    private Fun foo () = object {
        val x:string = "x"

    //Public function, so its return type is a NY fun
    publicfoo () = object {
        val x:string = ' x '
    } Fun

    Bar () {
        val x1 = foo (). x        //No problem
        Val x2 = Publicfoo (). x  //error: Failed to resolve reference "X"

Other variables in the scope can be easily accessed in object representations:

Fun Countclicks (window:jcomponent) {
    var clickcount = 0
    var entercount = 0

    Window.addmouselistener (object: Mouseadapter () {
        override mouseclicked (e:mouseevent) {
        } override fun

        mouseentered ( e:mouseevent) {
Object Declaration

Kotlin uses the OBJECT keyword to declare an object.

In Kotlin we can easily get a singleton by object declaration.

Object Dataprovidermanager

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