Kotlin 베이스 - object

1. Object 표현식

// Handler      
val handler: Handler = object: Handler() {
    override fun handleMessage(msg: Message?) {
        super.handleMessage(msg)
        when(msg?.what) {
            1 -> "Expression1"
            2 -> "Expression2"
        }
    }
}

/*
 *             ，         Anko        ；
 * TextView(ctx).setOnClickListener { 
 *     //...
 * }
 */
TextView(ctx).setOnClickListener(object: View.OnClickListener{
    override fun onClick(v: View?) {
        //...
    }
})

2. object 개체 선언

2.1 Object 객체 직접 선언

// Kt        ： object      ,            
object SingleObject {
    fun test() {
        //...
    }
}

//     ：  .   ()
class Main {
    fun test() {
        SingleObject.test() // class   ，      SingleObject.INSTANCE.test();    
    }
}

// ----------------          ---------------

//Kotlin      class    ：
public final class SingleObject {
   public static final SingleObject INSTANCE;

   public final void test() {
   }

   private SingleObject() {
      INSTANCE = (SingleObject)this;
   }

   static {
      new SingleObject();
   }
}

2.2 인터페이스(추상 클래스)의 대상 성명을 계승한다

// Kt     
object MyMachine: Machine() {
    override fun start() {
        //...
    }
}
abstract class Machine {
    abstract fun start()
    open fun stop() {}//   open           ，     final   ，     ；
}

// ----------------          ---------------

//         class  
public final class MyMachine extends Machine {
   public static final Single INSTANCE;

   public void start() {
      String var1 = "not implemented";
      throw (Throwable)(new NotImplementedError("An operation is not implemented: " + var1));
   }

   private MyMachine() {
      INSTANCE = (MyMachine)this;
   }

   static {
      new MyMachine();
   }
}

public abstract class Machine {
   public abstract void start();
   public void stop() {}
}

2.3 클래스 내 개체 선언

class Single {
    object Manage {//        ，   inner           
        fun execute() {
            //...
        }
    }
}

// ----------------          ---------------

public final class Single {
   //      
   public static final class Manage {
      public static final Single.Manage INSTANCE;

      public final void execute() {}

      private Manage() {
         INSTANCE = (Single.Manage)this;
      }

      static {
         new Single.Manage();
      }
   }
}

3. 반려자 Companion Object

3.1 일반적인 반생 대상

class MyClass {
    companion object Factory {
        val url = ""
        fun create(): MyClass = MyClass()
    }
}

//      ，       .        .   
MyClass.url
MyClass.create()

3.2 반생 대상에서 인터페이스 구현

interface Factory {
    fun create(): T
}

class MyClass {
    //         
    companion object : Factory {
        val url = ""
        //          
        override fun create(): MyClass = MyClass()
    }
}

//   
class Main {
    fun test() {
        setFactory(MyClass) //        MyClass  ，    MyClass     
    }

    fun  setFactory(factory: Factory) {
        factory.create()
    }
}

3.3 반생 대상의 확장

class MyClass {
    companion object Factory {
        fun create(): MyClass = MyClass()
    }
}

//       
fun MyClass.Factory.fun_name() = ...    ...

//   
MyClass.Factory.fun_name()