Java

The basic concept in Java is known as core java, it comprises the single tire architecture, util, lang, art, io and net packages. Core java also covers the concept of oops, wrapper class, special operator, datatypes, exception handling, stack, linked list, queue, array and list.
Core java means stand

Since you aren't a complete novice, I think you're ready for C++, for the following reasons:
It's dangerous. Some may think this is a reason to avoid it, but these are things you are going to have to learn.
It's close to the hardware. This makes it fast and optimization and also suitable for tiny litt

Best books for JAVA -
Head First Java, 2nd Edition - OReilly Media
Thinking in Java (4th Edition)
Java: A Beginners Guide (Sixth Edition) by Herbert Schildt
Introduction to Programming in Java by Robert Sedgewick
Introduction to Object-Oriented Programming with Java by C.Thomas wu
Java in a Nutshell
Begin

For pursuing PhD after MCA, you need to qualify for GATE and NET exam with a valid score.

For a Java developer, having a strong understanding of Object-Oriented Programming is a must.
Master the core APIs- It doesn't matter how strong you are in terms of theoretical knowledge if you don't know the language constructs and core APIs.
Keep coding- Things look simpler when talking about them

Some questions for JAVA developers -
Which is the superclass of all classes?
Differentiate between J2SDK 1.5 and J2SDK 5.0?
What are wrapper classes?
What is the ThreadLocal class? How and why would you use it?
What is the volatile keyword? How and why would you use it?
What is runtime polymorphism or dy

Python is the older of the two languages. In programming language evolution, it is common to maintain backward compatibility indefinitely. This is not the case with Python. Python versions are largely compatible but have enough functionality- and syntax-breaking differences that they can be treated

MBA and a career in IT are two different domains, you need not to have an MBA for a successful career in IT. Most of the people do MBA to get managerial roles in IT companies after working for 3 to 4 years in the IT sector.

In 20 days, you can only brush up the basic part in Java, learning any language completely is not possible in just 20 days, but I would recommend you to go ahead and learn as much as you can in 20 days and then sneak out few hours on a weekly basis to master Java.