How Do You Break A Singleton?

Can we serialize Singleton class?

Conclusion: Singleton class can also be serialized by keeping readResolve() method in the Singleton class.

This may be a familiar solution but just in case for reference.

So if we execute above code we will get following behaviour: “it has created two objects and one static reference for INSTANCE..

Where is Singleton pattern used?

In terms of practical use Singleton patterns are used in logging, caches, thread pools, configuration settings, device driver objects. Design pattern is often used in conjunction with Factory design pattern. This pattern is also used in Service Locator JEE pattern.

What is lazy and early loading of Singleton?

Both these refer to when the Singleton object gets created in the application. In lazy loading it is created only when the method creating the instance is first called. In early loading the instance is created once the class is loaded.

How can we avoid serialization in Singleton?

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. Overcome serialization issue:- To overcome this issue, we have to implement method readResolve() method. Above both hashcodes are same hence no other instance is created.

Can we override Singleton class?

The only way to override a singleton is to have a singleton that expects to be overridden. The simplest way to do this is to provide Singleton that implements an interface (or is otherwise fully abstract itself) that internally instantiates an injected singleton upon the first use of getInstance() .

Is Singleton class immutable?

A singleton can be mutable or immutable; a non-singleton can be mutable or immutable. … Your Student class is approximately singleton, but not immutable: any class where you have a setter method that mutates a member variable cannot be immutable.

Why is lazy vs eager initialization preferred?

Lazy initialization is technique were we restrict the object creation until its created by application code. This saves the memory from redundant objects which some time may be very big/heavy. In other way eager initialization creates the object in advance and just after starting the application or module.

What is lazy Singleton?

Lazy Initialization is a technique where one postpones the instantiation of a object until its first use. In other words the instance of a class is created when its required to be used for the first time. The idea behind this is to avoid unnecessary instance creation.

How do you break a singleton with reflection?

As it is not possible to call enum constructor from the program, it is not possible for us to access them by Reflection also. Hence, reflection can’t break singleton property in case of enums. Enum Singleton cannot be broken using Serialization and Enums are also by default thread-safe.

What are the ways to break Singleton?

Deserialization. In serialization, we can save the object of a byte stream into a file or send over a network. Suppose if you serialize the Singleton class, and then again de-serialize that object, it will create a new instance, hence deserialization will break the Singleton pattern.

Why is Singleton bad for testing?

While they provide a quick and easy solution, singletons are considered bad because they make unit testing and debugging difficult. … This property allows you to substitute alternate implementations for collaborators during testing to achieve specific testing goals (think mock objects).

What is eager instantiation and lazy loading in spring?

By default, Spring “application context” eagerly creates and initializes all ‘singleton scoped’ beans during application startup itself. It helps in detecting the bean configuration issues at early stage, in most of the cases.