[移动开发]kotlin 单例

实现方式1

class KLazilyDCLSingleton private constructor() : Serializable {//private constructor()构造器私有化

    fun doSomething() {
        println("do some thing")
    }

    private fun readResolve(): Any {//防止单例对象在反序列化时重新生成对象
        return instance
    }
    
    companion object {
        //通过@JvmStatic注解，使得在Java中调用instance直接是像调用静态函数一样，类似KLazilyDCLSingleton.getInstance(),
        //如果不加注解，在Java中必须这样调用: KLazilyDCLSingleton.Companion.getInstance().
        @JvmStatic
        //使用lazy属性代理，并指定LazyThreadSafetyMode为SYNCHRONIZED模式保证线程安全
        val instance: KLazilyDCLSingleton by lazy(LazyThreadSafetyMode.SYNCHRONIZED) { KLazilyDCLSingleton() }
    }
}

实现方式2

class KOptimizeSingleton private constructor(): Serializable {//private constructor()构造器私有化
	
    companion object {
        @JvmStatic
        fun getInstance(): KOptimizeSingleton {//全局访问点
            return SingletonHolder.mInstance
        }
    }

    fun doSomething() {
        println("do some thing")
    }
    
    private object SingletonHolder {//静态内部类
        val mInstance: KOptimizeSingleton = KOptimizeSingleton()
    }
    
    private fun readResolve(): Any {//防止单例对象在反序列化时重新生成对象
        return SingletonHolder.mInstance
    }
}

方式3：静态方法调用

class TopLevelClass {

    companion object {
        fun doSomeStuff() {
            ...
        }
    }

    object FakeCompanion {
        fun doOtherStuff() {
            ...
        }
    }
}

fun testCompanion() {
    TopLevelClass.doSomeStuff()
    TopLevelClass.Companion.doSomeStuff()
    TopLevelClass.FakeCompanion.doOtherStuff()
}