05设计模式-kotlin-单例模式Singleton

什么是单例模式

一句话说: 在程序中只存在一个实例.

直接代码

/**
 * Created by silen on 2018/7/7 23:30
 * Copyright (c) 2018 in FORETREE
 */

//懒汉式
class S1 private constructor() {
    companion object {
        private var mInstance: S1? = null

        fun getInstance(): S1? {
            if (mInstance == null) {
                mInstance = S1()
            }
            return mInstance
        }
    }
}
//线程安全
class S2 private constructor() {

    companion object {
        private var mInstance: S2? = null

        @Synchronized fun getInstance(): S2? {
            if (mInstance == null) {
                mInstance = S2()
            }
            return mInstance
        }
    }
}

//饿汉式
class S3 private constructor() {
    companion object {
        @JvmStatic private val instance = S3()

        fun getInstance(): S3 {
            return instance
        }
    }
}

//双重检测 DCL
class SDCL private constructor() {
    companion object {
        private var instance: SDCL? = null

        fun getInstance(): SDCL? {
            if (instance == null) {
                synchronized(SDCL::class.java) {
                    if (instance == null) {
                        instance = SDCL()
                    }
                }
            }
            return instance
        }
    }
}

//静态内部类
class Sin private constructor() {
    companion object {
        fun getInstance():Sin {
            return SHolder.holder
        }
    }

    class SHolder private constructor() {
        companion object {
            val holder = Sin()
        }
    }
}

fun main(args: Array<String>) {
    println("饿汉式 equal : ${S1.getInstance()==S1.getInstance()} ")
    println("线程安全 equal : ${S2.getInstance()==S2.getInstance()} ")
    println("懒汉式 equal : ${S3.getInstance()==S3.getInstance()} ")
    println("双重检测 equal : ${SDCL.getInstance()==SDCL.getInstance()} ")
    println("静态内部类 equal : ${Sin.getInstance()==Sin.getInstance()} ")
}

运行结果

饿汉式 equal : true 
线程安全 equal : true 
懒汉式 equal : true 
双重检测 equal : true 
静态内部类 equal : true 

注意的是构造方法一定要私有化.