What is List interface ?

List is an ordered collection of objects.

Considering the basic properties of Vector and ArrayList, where will you use Vector and where will you use ArrayList?

The basic difference between a Vector and an ArrayList is that, vector is synchronized while ArrayList is not. Thus whenever there is a possibility of multiple threads accessing the same instance, one should use Vector. While if not multiple threads are going to access the same instance then use ArrayList. Non synchronized data structure will give better performance than the synchronized one.

Explain the Polymorphism principle.

The meaning of Polymorphism is something like one name many forms. Polymorphism enables one entity to be used as as general category for different types of actions. The specific action is determined by the exact nature of the situation. The concept of polymorphism can be explained as "one interface, multiple methods".

Explain the Inheritance principle.

Inheritance is the process by which one object acquires the properties of another object.

Explain the Encapsulation principle.

Encapsulation is a process of binding or wrapping the data and the codes that operates on the data into a single entity. This keeps the data safe from outside interface and misuse. One way to think about encapsulation is as a protective wrapper that prevents code and data from being arbitrarily accessed by other code defined outside the wrapper.

What is OOPS?Describe the principles of OOPS.

OOPS is the common abbreviation for Object-Oriented Programming.There are three main principals of oops which are called Polymorphism, Inheritance and Encapsulation.

Explain the usage of Java packages.

This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. Packages access level also allows you to protect data from being used by the non-authorized classes.