【Android】Java的单例在Kotlin的5种实现

深碍√TFBOYSˉ_ 2022-09-17 06:20 7阅读 0赞

### Java的单例在Kotlin的5种实现 ###

*  饿汉式
 *  懒汉式
 *  线程安全的懒汉式
 *  双重校验锁式
 *  静态内部类式

# 饿汉式 #

`Java`

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

`Kotlin`

object Singleton

# 懒汉式 #

`Java`

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

`Kotlin`

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

# 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 = SingletonDemo()
                    }
                    return field
                }
                
            @Synchronized
            fun get(): SingletonDemo{
                return instance!!
            }
        }
    }

# 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`

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

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 SingletonHolder{
            private static Singleton instance=new Singleton();
        }
        
        private Singleton(){}
        
        public static SingletonDemo getInstance(){
            return SingletonHolder.instance;
        }
    }

`kotlin`

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