Question: Can Singleton Class Be Serialized?

How can we avoid serialization in Singleton?

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..

Can a singleton class be inherited?

Unlike static classes, Singleton classes can be inherited, can have base class, can be serialized and can implement interfaces. You can implement Dispose method in your Singleton class.

Why do we need Singleton class?

The purpose of the singleton class is to control object creation, limiting the number of objects to only one. The singleton allows only one entry point to create the new instance of the class. … Singletons are often useful where we have to control the resources, such as database connections or sockets.

What is singleton class example?

Singleton Class in Java. In object-oriented programming, a singleton class is a class that can have only one object (an instance of the class) at a time. After first time, if we try to instantiate the Singleton class, the new variable also points to the first instance created.

When a singleton is not Singleton in Java?

A singleton (in Java land) wouldn’t work as a singleton if a given class is loaded by multiple class-loaders. Since a single class can exist (or can be loaded) in multiple classloaders, it’s quite possible to have “multiple” instances of a “supposedly” singleton class for a given JVM instance.

Where is singleton class used?

Singleton classes are used for logging, driver objects, caching and thread pool, database connections. An implementation of singleton class should have following properties: It should have only one instance : This is done by providing an instance of the class from within the class.

How can we avoid Singleton by reflection serialization and cloning?

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. Cloning: Cloning is a concept to create duplicate objects. Using clone we can create copy of object.

Is string serializable in Java?

The String class and all the wrapper classes implement the java. io. Serializable interface by default.

How can we prevent immutable class from serialization?

If an immutable object was serialized, its raw bytes could be modified so that upon deserialization the object is no longer the same. This can’t be prevented completely. Encryption, checksums, and CRC’s will help to prevent this though. You should read Effective Java written by Joshua Bloch.

How do you make a class singleton in Java?

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.More items…

Which method can help you serialize Singleton class such that object returned by DeSerialization process is in same state as it was during serialization time in Java?

Can you Serialize Singleton class such that object returned by Deserialization process is in same state as it was during Serialization time (regardless of any change made to it after Serialization)? Defining readResolve() method ensures that we don’t break singleton pattern during DeSerialization process.

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.

Why is Singleton bad?

By using singletons in your project, you start to create technical debt. Singletons tend to spread like a virus because it’s so easy to access them. It’s difficult to keep track of where they’re used and getting rid of a singleton can be a refactoring nightmare in large or complex projects.

What is readResolve method in Java?

For Serializable and Externalizable classes, the readResolve method allows a class to replace/resolve the object read from the stream before it is returned to the caller. By implementing the readResolve method, a class can directly control the types and instances of its own instances being deserialized.

How can we prevent Singleton class from cloning?

It is necessary if your Singleton class extends a class that has a visible clone() method defined in its hierarchy. You can avoid cloning by giving already created object by clone method.

Why is serialization required?

Serialization is usually used When the need arises to send your data over network or stored in files. By data I mean objects and not text. … Serialization is the translation of your Java object’s values/states to bytes to send it over network or save it.

Can we clone singleton class in Java?

clone() is protected method and as every class in java by default extends Object class, object of any class including our Singleton class can call clone() method. If somebody will call instance. … So, if we are not implementing Cloneable interface in our Singleton class, then we do not require to prevent cloning.

How can we prevent immutable class from reflection?

How to Make Classes ImmutableDefine class as final.Make all fields private and final.Make the constructor private, and use public factory methods.Make sure all setter methods are made private or remove them altogether.