Kotlin的5种单利写法和java对比

​​​​​​主要单例模式实现如下：

• 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

一，饿汉式实现

（1）java恶汉式

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

（2）Kotlin饿汉式

//kotlin单例
object Singleton{

}

 

二，懒汉式实现

（1）java懒汉式

//Java实现
public class Singleton {
    private static Singleton instance;
    private Singleton(){}

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

（2）kotlin懒汉式

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

 

三，线程安全的懒汉式

（1）java线程安全的懒汉式

//Java实现
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;
    }
}

（2）kotlin线程安全的懒汉式

//Kotlin实现
class Singleton private constructor() {
    companion object {
        private var instance: Singleton? = null
            get() {
                if (field == null) {
                    field = Singleton()
                }
                return field
            }
        @Synchronized   //引入 org.jetbrains.kotlin:kotlin-stdlib-jdk7
        fun get(): Singleton{
            return instance!!
        }
    }
}

 

四，双重校验锁式

（1）java双重校验锁式

//Java实现
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;
    }
}

（2）kotlin双重校验锁式

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

 

五，静态内部类式

（1）java静态内部类式

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

    private Singleton() {
        System.out.println("Singleton has loaded");
    }

    public static Singleton getInstance() {
        return SingletonHolder.instance;
    }
}

（2）kotlin静态内部类式

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

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