饿汉式

public class SingletonOne {
    //1.创建类中私有构造
    private SingletoneOne(){
        
    }

    //2.创建该类型的私有静态实例
    private static SingletonOne instance = new singletonOne();
    
    //3.创建公有的静态方法返回静态实例对象
    public static SingletonOne getInstance(){
        return instance;
    }
}

懒汉式

public class SingletonOne {
    //1.创建类中私有构造
    private SingletoneOne(){
        
    }

    //2.创建该类型的私有静态实例
    private static SingletonOne instance = null;
    
    //3.创建公有的静态方法返回静态实例对象
    public static SingletonOne getInstance(){
        if (instance == null){
            instance = new SingletonOne();
        }
        return instance;
    }
}