A type of programming in which programmers define not only the data type of a data structure, but also the types of operations (functions) that can be applied to the data structure. In this way, the data structure becomes an object that includes both data and functions. In addition, programmers can create relationships between one object and another. For example, objects can inherit characteristics from other objects.
One of the principal advantages of object-oriented programming techniques over procedural programming techniques is that they enable programmers to create modules that do not need to be changed when a new type of object is added. A programmer can simply create a new object that inherits many of its features from existing objects. This makes object-oriented programs easier to modify.
To perform object-oriented programming, one needs an object-oriented programming language (OOPL). Java, C++ and Smalltalk are three of the more popular languages, and there are also object-oriented versions of Pascal.
In a Simple way ..
As per the definition of Object Oriented Programming, a language can be categorized as PURE OOP based on following criteria:
The language must have inbuilt support for encapsulation and abstraction.
The language must have inbuilt support for Inheritance.
The language must have inbuilt support for Polymorphism.
All system defined types must be objects.
All user defined types must be object.
The only way of communication between objects is through the methods exposed on the same.
Criteria 1 to 3 are self explanatory and don’t require further clarification. So I am escaping those. Now consider criteria 4.
Criteria 4 states that all predefined types in the systems must be objects only. This means there can’t be anything other than objects defined by system. This is the first requirement where Java fails to fulfill the criteria to be categorized as pure Object Oriented Programming. Java has primitive types, which are not objects and thus violates this rule.
Criteria 5 suggests that all user defined types must also be objects only. This means users can’t define or create anything other than objects. This restriction is not applicable in using system defined types. Java successfully follows this rule where user can’t create or define anything other than objects.
Criteria 6 suggest that whenever objects communicate with each other, they communicate using the methods exposed on other objects. And this should be the only way of communication. Java violets this rule by using various operators. Consider the ‘+’ operator on String literals which can be used to add 2 or more string objects. By using this operator java violets the rule of object communication using methods. This holds true for other operators on primitive types as well.
Summing up the above points, java fulfils the criteria 1,2,3,5 but fails in 4 and 6. Failing of these 2 criteria deprived java from being categorized as PURE Object Oriented Programming Language. But still the programming community categorizes Java as OOP (although not Pure). In theory such languages are called ‘Hybrid OOP’ languages.