kotlin单列

一、饿汉模式

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

//Kotlin实现
object SingletonDemo{}

二、懒汉模式

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

//kotlin实现
方式一、构造方法无参数
class Singleton private constructor(){
    companion object{
        val instance: Singleton by lazy { Singleton() }
    }
}
方式二、构造方法携带参数
class Singleton private constructor(id: String){
    companion object{
        private var mInstance: Singleton? = null

        fun getInstance(id: String): Singleton{
            return mInstance ?: Singleton(id).also { mInstance = it }
        }
    }
}

三、线程安全懒汉模式

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

//kotlin实现
方式一、构造函数无参数
class Singleton private constructor(){
    companion object{
        private val mInstance: Singleton by lazy { Singleton() }

        @Synchronized
        fun getInstance(): Singleton{
            return mInstance
        }
    }
}
方式二、构造函数有参数
class Singleton private constructor(id: String){
    companion object{
        private var mInstance: Singleton? = null

        @Synchronized
        fun getInstance(id: String): Singleton{
            return mInstance ?: Singleton(id).also { mInstance = it }
        }
    }
}

四、双重校验锁模式

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

//kotlin实现
方式一、构造函数无参数
class Singleton private constructor(){
    companion object{
        val instance: Singleton by lazy(mode = LazyThreadSafetyMode.SYNCHRONIZED) {
        Singleton() }
    }
}
方式二、构造函数有参数
class Singleton private constructor(id: String){
    companion object{
        private var mInstance: Singleton? = null

        fun getInstance(id: String): Singleton{
            return mInstance?: synchronized(this){
                mInstance?: Singleton(id).also { mInstance = it }
            }
        }
    }
}

五、静态内部类

//Java实现
public class Singleton {
    private static class SingletonHolder{
        private static Singleton instance=new Singleton();
    }
    private Singleton(){
    }
    public static Singleton getInstance(){
        return SingletonHolder.instance;
    }
}
//kotlin实现
class Singleton private constructor() {
    companion object {
        val instance = SingletonHolder.holder
    }

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

六、java调用kotlin单例

1、object创建的单例

Singleton.INSTANCE.test();

2、companion创建的单例

Singleton.Companion.getInstance().test();

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