Is the mechanism that protects data and code within an object from misuse by other routines

OOP basics

Adopting object-orientated programming starts with learning to clearly identify objects and define their relationships through data modeling and class designations. This requires developers to understand the following three main components of OOP:

• Objects. Collections of data and procedures that are grouped into single, reusable entities. Objects feature two major characteristics: data (describes an object's state and its unique characteristics) and behavior (indicates how it interacts with other objects).
• Methods. Developers invoke methods to manipulate data and perform specific tasks. Developers can also invoke methods that make code more compact and reusable.
• Classes. These define the state, behavior and identity of every object. Classes help developers understand the set of properties associated with an object or shared among a group of objects.

Let's look at an example of how these components interact. In Java, class designation instructs the Java virtual machine (JVM) environment to build an object. Using a single class definition, a programmer can build multiple objects into a software program. This allows for faster parallel development, modular class reuse and a higher degree of maintainability.

OOP principles

Object-oriented programming is better defined as a set of guiding concepts than as a technical method. Specifically, there are four overarching OOP principles:

1. Inheritance

Developers can simultaneously reuse common logic among unique objects, but only if they assign hierarchic relationships and subclasses to those objects. If a particular class is able to inherit fields and methods from a superior class, programmers can better manage the integration of all the objects involved.

Class inheritance moves from the top of the hierarchy down, with the top made up of superclasses (also called parent classes). A superclass can maintain any number of subclasses, but a single subclass should never associate with more than one superclass.

2. Polymorphism

Polymorphism means that objects can adopt more than one form, depending on their context. The application should then be able to independently recognize the correct form and execute the code and run the object's associated methods. This creates clear boundaries between entities that share same name with signatures and declarations, and is the key OOP mechanism that allows components to share behavior.

It's worth noting that polymorphism takes two unique forms in Java coding:

• Compile time polymorphism, where objects can share the same static name, despite embodying different parameters; and
• Runtime polymorphism, which enables a subclass (or child class) to activate a method provided by one of its parent classes at runtime.

3. Reusability

When developers want to create a new class, but an existing class already contains the desired code, they can derive a new class from the old one. In OOP, these modular classes enable developers to reuse those classes in other applications and projects.

This reusability opens the door for programmers to perform fixed sets of operations on particular objects, and then add functionality as the application and codebase evolves. However, improper use of inheritance, such as leaving unused data in base classes, can lead to memory mismanagement and application failures.

4. Encapsulation

Encapsulation represents the mechanism for code to bind with the data it manipulates. This provides a shield that protects data from being accessed by any external code existing outside this shield. When that data is hidden, only a declared function within that class can access the variables or data. This will both prevent unauthorized objects, as well as contain failures that would otherwise spread to other components.

Java: The influential OOP language

Java embodies the best qualities of OOP, namely since it is defined as a "write once, run anywhere" language. Programmers can achieve high reusability from Java code, especially since the code can essentially run on any device or platform through the JVM interpreter. Once compiled, Java programs are converted into bytecode, which can be recompiled at each particular system platform.

For example, Java programmers can make it easier to maintain procedural code through basic OOP concepts. Since the language encourages a centralized code base, developers can quickly and easily access that data during upgrades. This centralization also improves programming security, since Java requires high levels of validation.

Finally, Java employs data abstractions that present only the essential details of an object to a particular user. By noting the properties and behaviors of objects, Java programmers can delineate similar types of objects from one another, and then implement interfaces and abstract classes. This leads to a situation where only the relevant operations will interact with certain data types.