How can we break a Singleton class?

Question

Accepted Answer

Singleton class can be broken using reflection, serialization, cloning, and multi-threading.

Reflection can be used to access the private constructor and create multiple instances.
Serialization can create multiple instances when the object is deserialized.
Cloning can create a new instance of the Singleton class.
Multi-threading can create multiple instances if not synchronized properly.

Accepted Answer

We can break a singleton class using any of the below mentioned ways:
Cloning: By utilizing the clone() method, one can create a duplicate of the singleton object, thereby violating its intended uniqueness.

Reflection: Accessing the private constructor through the getDeclaredConstructor() method and setting it to accessible with setAccessible(true) allows for the creation of a new instance, effectively breaking the singleton property.

Serialization/Deserialization: Implementing the Serializable interface enables the serialization of the singleton object, followed by deserialization, which can result in the creation of an additional instance.

Multithreading: In an unsynchronized singleton implementation, multiple threads can concurrently access the getInstance() method. If they do so while the instance is still null, this can lead to the creation of multiple instances, undermining the singleton pattern.