How can we prevent singleton from reflection using enum?
How to prevent Reflection API from breaking Singleton
- private ReflectionSingleton() { if (instance != null ) {
- throw new IllegalStateException( “instance already created.” ); }
- System.out.println( “Singleton instance is being created.” ); }
How do I make a singleton class?
To create the singleton class, we need to have static member of class, private constructor and static factory method.
- Static member: It gets memory only once because of static, itcontains the instance of the Singleton class.
- Private constructor: It will prevent to instantiate the Singleton class from outside the class.
How is a singleton related to a class?
A singleton is an instance of a class, managed in such a way that only one instance is possible to create. A static variable is similarly tied to exactly one (static) instance of a class, but could be assigned with not only a class instance but any data type such as a scalar.
How to prevent breaking a singleton class pattern in Java?
To overcome the above issue, we need to implement/override the clone () method and throw an exception CloneNotSupportedException from the clone method. If anyone tries to create a clone object of Singleton, it will throw an exception, as shown in the below code.
What happens when you de-serialize a singleton class?
Then if you de-serialize that object it will create a new instance and hence break the singleton pattern. As you can see, hashCode of both instances is different, hence there are 2 objects of a singleton class. Thus, the class is no more singleton.
How to instantiate a singleton class in Java?
In the main class, we instantiate the singleton class with 3 objects x, y, z by calling static method getInstance(). But actually after creation of object x, variables y and z are pointed to object x as shown in the diagram. Hence, if we change the variables of object x, that is reflected when we access the variables of objects y and z.