【Android,kotlin设计模式】Java的单例在Kotlin的5种实现

mozhimen

已于 2022-07-29 13:48:51 修改

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分类专栏： # Kotlin 文章标签： kotlin java

于 2021-12-22 14:26:05 首次发布

本文链接：https://blog.csdn.net/weixin_42473228/article/details/122084493

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本文介绍了Kotlin中实现单例模式的五种方法：饿汉式、懒汉式、线程安全的懒汉式、双重校验锁式及静态内部类式，并对比了相应的Java实现。

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1.饿汉式

Java

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

Kotlin

object Singleton {}

2.懒汉式

Java

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

Kotlin

//方法一
class Singleton private constructor() {
    companion object {
        private var instance: Singleton? = null
            get() {
                if (field == null) {
                    field = Singleton()
                }
                return field
            }
        fun get(): Singleton{
        	return instance!!
        }
    }
}

//方法二
class Singleton private constructor() {
    companion object {
        private var instance: Singleton? = null
            
        fun get(xx: String): Singleton{
        	if (instance== null) {
            	instance= Singleton(xx)
			}
        }
    }
	
	private constructor(xxx: String){
	}
}

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

3.线程安全的懒汉式

Java

public class Singleton {
    private static Singleton instance;
    
    private Singleton(){}
    
    public static synchronized Singleton getInstance(){//使用同步锁
        if(instance==null){
            instance=new Singleton();
        }
        return instance;
    }
}

Kotlin

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

4.双重校验锁式

Java

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

kotlin

//方式一
class Singleton private constructor() {
    companion object {
        val instance: Singleton by lazy(mode = LazyThreadSafetyMode.SYNCHRONIZED) {
			Singleton()
        }
    }
}

//方式二
class Singleton private constructor(private val xxx: String) {//这里可以根据实际需求发生改变
  
    companion object {
        @Volatile 
        private var instance: Singleton? = null
        
        fun getInstance(xx: String) =
                instance ?: synchronized(this) {
                    instance ?: Singleton(xx).also { instance = it }
                }
    }
}

静态内部类式

Java

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

kotlin

class Singleton private constructor() {
    companion object {
        val instance = SingletonProvider.holder
    }

    private object SingletonProvider{
        val holder= Singleton()
    }
}