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I am reviewing the concept of inner classes in java. so far from what I've understood and applied java inner classes has a link or access to the methods and fields of its outer/ enclosing class.
My Question:
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The main advantages of a nested (inner) class are: It shows a special type of relationship, in other words, it has the ability to access all the data members (data members and methods) of the main class including private. They provide easier code because it logically groups classes in only one place.
Inner classes are used to develop a more readable and maintainable code because they logically group classes and interfaces in one place. Easy access, as the inner object, is implicitly available inside an outer Code optimization requires less code to write. It can avoid having a separate class.
Inner classes are a security mechanism in Java. We know a class cannot be associated with the access modifier private, but if we have the class as a member of other class, then the inner class can be made private. And this is also used to access the private members of a class.
It can access any private instance variable of the outer class. Like any other instance variable, we can have access modifier private, protected, public, and default modifier. Like class, an interface can also be nested and can have access specifiers.
Inner classes are best for the purpose of logically grouping classes that are used in one-place. For example, if you want to create class which is used by ONLY enclosing class, then it doesn't make sense to create a separate file for that. Instead you can add it as "inner class"
As per java tutorial:
Compelling reasons for using nested classes include the following:
- It is a way of logically grouping classes that are only used in one place.
- It increases encapsulation.
- It can lead to more readable and maintainable code.
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A classic use for an inner class is the implementation of an iterator inside a container (ArrayList, for example - look for class Itr). All the container wants to expose to the rest of the world is an Iterator. However, it has to create some concrete implementation of that iterator, possibly familiar with the internals of the container. Using an inner class hides the implementation, while keeping it close to the container's implementation. And being inner (i.e. non-static), it is bound to a specific instance of that container, which lets it access private container members.
There are a few types of inner classes - non-static nested class, local classes and anonymous classes. Each one has a somewhat different purpose, so when asking about an inner class, you should specify what kind are you talking about.
Assuming you're referring to non-static inner classes, I'd say the reason to use them is the same as using regular classes (namely abstraction and dividing code into logical units), but there's no reason to make this use of classes visible to the rest of the world. You can also make nested classes public, of course, in which case you'd make them nested instead of independent in order to express their tight relation with the outer class.
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