In Java, an object stores its internal states in its instance variables (also known as member variables or fields). These instance variables represent the attributes of the object and can have different access levels (private, protected, public, or default) depending on the encapsulation requirements.
Mechanisms or structures typically used to represent and manage these states include:
1. Instance Variables (Fields):
These are declared inside a class but outside any method, and they are created when an object of the class is instantiated. Their values can be unique to each instance.
Constructors are special methods used to initialize objects, especially their internal states. They can be used to set default values or to set values provided during object instantiation.
3. Accessors (Getters) and Mutators (Setters):
These are methods used to retrieve (getters) and modify (setters) the values of instance variables. Using them helps maintain the principle of encapsulation, as it allows for controlled access to the internal states of an object.
Beyond getters and setters, objects can have other methods that act upon their internal states, providing behavior associated with the object.
Access modifiers (`private`, `protected`, `public`, and default) determine the visibility of instance variables and methods, helping in encapsulation and determining who can change or access the internal states.
6. Static Variables:
These are class-level variables that are shared among all instances of the class. While they can store a state, it's not unique to any single object instance.
7. Inner or Nested Classes:
Sometimes, an object's state might be best represented using another class. In these cases, one can use inner or nested classes to encapsulate that specific state and behavior within the outer class.
8. Enumerations (enums):
For states that have a predefined set of values, enums can be used. They provide a type-safe way to define and use constants.
9. Collections (e.g., Lists, Maps, Sets):
When an object's state consists of multiple values or when it needs to maintain a collection of other objects, Java's Collections Framework provides a rich set of interfaces and classes to store and manage such states.