1.objenesis
About
Objenesis is a small Java library that serves one purpose:
- To instantiate a new object of a particular class.
When would you want this?
Java already supports this dynamic instantiation of classes using Class.newInstance(). However, this only works if the class has an appropriate constructor. There are many times when a class cannot be instantiated this way, such as when the class contains:
- Constructors that require arguments.
- Constructors that have side effects.
- Constructors that throw exceptions.
As a result, it is common to see restrictions in libraries stating that classes must require a default constructor. Objenesis aims to overcome these restrictions by bypassing the constructor on object instantiation.
Typical uses
Needing to instantiate an object without calling the constructor is a fairly specialized task, however there are certain cases when this is useful:
- Serialization, Remoting and Persistence - Objects need to be instantiated and restored to a specific state, without invoking code.
- Proxies, AOP Libraries and Mock Objects - Classes can be subclassed without needing to worry about the super() constructor.
- Container Frameworks - Objects can be dynamically instantatiated in non-standard ways.