1、原始的单利方式（多线程并发，会重复new对象，不推荐使用）
Android

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

kotlin

class MyInstance {
    companion object{
        val instance by lazy(LazyThreadSafetyMode.NONE){
            MyInstance()
        }
    }
}

2、添加线程锁（实现了单例，但是效率降低了，不推荐使用）
Android

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

Kotlin

class MyInstance {
    companion object{
        private var instance:MyInstance?=null
         @Synchronized
        fun get():MyInstance{
            if(null==instance)instance=MyInstance()
            return instance as MyInstance
        }
    }
}

3、双层加锁判断，并且线程安全（推荐使用）

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

Kotlin

class MyInstance {
    companion object{
        val instance by lazy(LazyThreadSafetyMode.SYNCHRONIZED){
            MyInstance()
        }
    }
}