[Kotlin] 单例的写法

// 单例关键字object，声明为单例类之后会立即在内存中创建单例对象，并一直存在。

object BigHeadSon:IWashBow {    

    override fun washBow() {

        println("洗碗赚100000000元钱")

    }

}



fun main(args: Array<String>) {

    BigHeadSon.washBow()

}

// Java实现

public class SingletonDemo {

    private static SingletonDemo instance = new SingletonDemo();

    private SingletonDemo(){



    }

    public static SingletonDemo getInstance(){

        return instance;

    }

}



// Kotlin实现

object SingletonDemo

// Java实现

public class SingletonDemo {

    private static SingletonDemo instance;

    private SingletonDemo(){}

    public static SingletonDemo getInstance(){

        if(instance == null){

            instance = new SingletonDemo();

        }

        return instance;

    }

}



// Kotlin实现

class SingletonDemo private constructor() {

    companion object {

        private var instance: SingletonDemo? = null

            get() {

                if (field == null) {

                    field = SingletonDemo()

                }

                return field

            }

        fun get() : SingletonDemo {

        // 细心的小伙伴肯定发现了，这里不用getInstance作为为方法名，是因为在伴生对象声明时，内部已有getInstance方法，所以只能取其他名字

         return instance!!

        }

    }

}