Encapsulation is the process of wrapping up of data (properties) and behavior (methods) of an object into a single unit; and the unit here is a Class (or interface). Encapsulate in plain English means to enclose or be enclosed in or as if in a capsule. In Java, everything is enclosed within a class or interface, unlike languages such as C and C++ where we can have global variables outside classes. 

Inheritance describes the parent child relationship between two classes.

A class can get some of its characteristics from a parent class and then add more unique features of its own. For example, consider a Vehicle parent class and a child class Car. Vehicle class will have properties and functionalities common for all vehicles. Car will inherit those common properties from the Vehicle class and then add properties which are specific to a car.

The ability to change form is known as polymorphism. Java supports different kinds of polymorphism like oveloading and overriding.

Overloading

The same method name (method overloading) or operator symbol (operator overloading) can be used in different contexts.

In method overloading, multiple methods having same name can appear in a class, but with different signature. And based on the number and type of arguments we provide while calling the method, the correct method will be called.

Let us quickly see object oriented analysis, object oriented design, object oriented implementation using a 'Library Management System' example.

Object-Oriented Development uses "objects" to model real world objects. A car or a laptop can be considered as object. While traditional programming views software as a collection of functions, an object oriented system concentrates on the objects that combines data and functionality together.

The traditional approach mostly focussed on structured system development and the technique used was usually referred to as the Structured Analysis and Design Technique (SADT).