1、使用object声明类似java中的静态内部类

interface Moveable{
      fun move(){
      }
}

class Outer{
         private var a:String?=null
          //被编译成静态内部类
          object c:Moveable{
                  override fun move() {
                       //接口的默认实现
                        super.move()
                        //静态内部类无法访问外部内非静态变量
                        //print(a)
                    }
            }
}

编译后生成的class文件

使用 jad 将class文件转java
jad -s .java Outer.class

public final class Outer
{
    public static final class c
        implements Moveable
    {

        public void move()
        {
            Moveable.DefaultImpls.move(this);
        }

        public static final c INSTANCE = (c)this;

        static 
        {
            new c();
        }

        private c()
        {
        }
    }


    public Outer()
    {
    }

    private String a;
}

jad -s .java Moveable.class

public interface Moveable
{
    public static final class DefaultImpls
    {

        public static void move(Moveable moveable)
        {
        }
    }
    public abstract void move();
}

jad -s .java Moveable$DefaultImpls.class

public static final class Moveable$DefaultImpls
{

    public static void move(Moveable moveable)
    {
    }
}

jad -s .java Outer$c.class

public static final class Outer$c
    implements Moveable
{

    public void move()
    {
        .DefaultImpls.move(this);
    }

    public static final Outer$c INSTANCE = (Outer$c)this;

    static 
    {
        new Outer$c();
    }

    private Outer$c()
    {
    }
}

2、使用object声明类似java中的匿名内部类

interface Moveable{
   fun move(){

   }
}


class Outer{
   private var a:String?=null
   //被编译成匿名内部类
   private var c = object:Moveable {
       override fun move() {
           //接口的默认实现
           super.move()
           print(a)
       }
   }
}

编译后生成的class文件

public static final class Outer$c$1
    implements Moveable
{

    public void move()
    {
        efaultImpls.move(this);
        String s = Outer.access$getA$p(Outer.this);
        System.out.print(s);
    }

    final Outer this$0;

    Outer$c$1(Outer $outer)
    {
        this$0 = $outer;
        super();
    }
}

public final class Outer
{

    public Outer()
    {
        c = new Moveable(this) {

            public void move()
            {
                Moveable.DefaultImpls.move(this);
                String s = a;
                System.out.print(s);
            }

            final Outer this$0;

            
            {
                this$0 = $outer;
                super();
            }
        }
;
    }

    private String a;
    private c._cls1 c;


}

3、使用object声明单例对象

object Singleton{
    fun f1() {

    }

    fun f2() {

    }
}

java代码

public final class Singleton
{

    public final void f1()
    {
    }

    public final void f2()
    {
    }

    private Singleton()
    {
    }

    public static final Singleton INSTANCE = (Singleton)this;

    static 
    {
        new Singleton();
    }
}