Kotlin中的单例模式与Java对比

Java基础

浏览数:190

2019-8-22

目前java中的单例模式有多种写法,kotlin中的写法更多一点,本篇会总结全部的到单例模式写法。

一、懒人写法(恶汉式)

java中

  public class Singleton{
        public static final Singleton instance = new Singleton();
        public Singleton getInstance() {
              return instance;
        }
  }

kotlin中

最简单的写法,直接用object声明

object Singleton{}

二、基本懒加载(未实现线程同步)

注:这种方式实现了懒加载,但是不是线程安全的,可能在多个线程中创建多个不同的实例

java中

public class Singleton {
      public static Singleton instance = null;
      private Singleton (){}
      public Singleton getInstance() {
            if (instance == null) {
                instance = new Singleton();
            }
            return instance;
       }
}

kotlin中

class Singleton private constructor{
    companion object {
          val intance by lazy(LazyThreadSafetyMode.NONE) { Singleton() }
    }
}

三、线程同步单例1

注:其实kotlin这种写法可以说是java直译过来的,虽说是线程安全的,但是太影响效率,主要看下面这种

java中

public class Singleton {
      private static Singleton instance = null;
      private Singleton (){}
      public static synchronized  Singleton getInstance() {
            if (instance == null) {
                instance = new Singleton();
             }
            return instance;
        }
 }

kotlin中

class Singleton private constructor(){
        companion object {
            lateinit var instance: Singleton
            @Synchronized
            fun get(): Singleton {
                    if (instance == null) {
                          instance = Singleton();
                     }
                return instance!!
            }
      }
}

四、线程同步单例2

注:线程同步,懒加载,无同步引起的效率问题

java中双检锁单例

public class Singleton {
      private static  Singleton instance = null;
      private Singleton (){}
      public static Singleton getInstance() {
            if (instance == null) {
            synchronized (Singleton.class) {
                  if (instance == null) {
                      instance = new Singleton();
                  }
             }
      }
      return instance;
  }
}

kotlin

class Singleton private constructor(){
      companion object {
          val intance by lazy(LazyThreadSafetyMode.SYNCHRONIZED) { Singleton() }
  }
}

五、静态内部类单例

java中

public class Singleton {
    private Singleton (){}
    private static class Holder {
    private static Singleton instance = new Singleton();
    }
    public static Singleton getInstance(){
        return Holder.instance;
    }
}

kotlin中

class Singleton private constructor(){
      companion object {
          fun getInstance(): Singleton {
              return Holder.instance
          }
      }
      private object Holder {
          val instance = Singleton()
      }
  }

最后,希望此篇博客对大家有所帮助,欢迎提出问题及建议共同探讨,如有兴趣可以关注我的博客,谢谢!

作者:会撒娇的犀犀利