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Learn Core Java, in 30 days as an Absolute Beginner

a roadmap...

 Core Java can be Overwhelming, in the beginning!

Let's see what are those topics you should cover and what you can skip in Core Java.
1. Theoretical Concepts (2 days)

- Features of Java
- JVM, JRE & JDK
- Memory areas in Java
- Basics of how Garbage Collection Works.
2. OOP Concepts (3 days)

- Objects and Classes
- Inheritance
- Polymorphism
- Encapsulation

This topic forms the basis of your Java learning. Spent enough time on this topic and understanding it using real-world examples and some practicals.
https://t.co/VFImq1o2uW
3. Primitives data types, Operators & Arrays (3 days)

- Various primitives/non-primitives data types, operators
- What is their use, How to use them
- Various sizes of data types
- Arrays, practice a few of its problems
- 2D/3D arrays and their use cases, practice a few problems
4. Packages and Access Modifiers (2 days)

- Default package, Normal package and its use case
- Various access modifiers and how they behave in different types of packages.
- Write a few programs to practice

https://t.co/kCrMArRhmC
5. Conditional Statements and Loops (2 days)

- While/Do While
- For loops
- If/else conditions
- Switch case
6. Objects, Classes & Interface (4 days)

- Objects
- Abstract Class/Concrete Class
- Constructors, Methods
- Interface
- What is Inheritance through classes and interfaces
- Method Overloading/Overriding
- static, final keywords
7. Basics of Multithreading (2 days)

- What is threads, How do create them.
- Thread class, hierarchy
- Learn to create simple threads using Thread class and using Runnable.
- Various methods of Thread class
- Write some program to practice

https://t.co/C7JfpMCgdV
8. Exception Handling (3 days)

- Problem solved by Exception Handling
- Exception Hierarchy
- Checked/Unchecked Exception
- How to create custom exception
- throw, throws, throwable, try-catch, finally
9. Collections (5 days)

- Basics of Collections
- Classes/Interface with its hierarchy in Collection framework.
- All about List, Set & Map, their differences, internal data structures and internal working.
- Collections util class
10. Lambda & Streams (3 days)

- What are lambda functions & why is it introduced
- Functional Interface and Functional Programming
- Write programs to practice
- Streams API and its methods.
- Stream pipelines and their methods

https://t.co/XqJlbBdpb6
Tips:

1. Skip these Topics:
- Advance Multithreading Concepts
- Swing/Applet
- Java. util package
- Java. io package

2. Prepare a daily plan, and spent 5-8 hrs daily to achieve this goal.

3. Don't fall into tutorial hell, write programs at every stage.
Conclusion:

Don't hardwire that these are the only topics you should know in Core Java, the rest is garbage.

No. That's not true!

But as an absolute beginner, you should at least know this much while the rest of the topics you will discover as and when you need.

More from Vikas Rajput

Vikas Rajput
Vikas Rajput
@vikasrajputin
Java: Acess Modifiers

a thread...

(Cheatsheet Included)

What is an access modifier?

Access Modifiers are a way of providing limited visibility to methods, variables, classes.

Different access modifiers provide different visibility due to which our program because less prone to unwanted changes.

Java has four access modifiers, let's see each one by one

public:
It's the least restrictive access modifier when any class, method, or variable is defined as public then it is accessible from anywhere.

protected:
Protected methods & variables can be accessed within the same package and also accessible to all child classes.

default:
When no access modifier is specified then java treats it as default. With default methods & variables are accessible within the same package.

private:
It's the most restrictive access modifier, when given to any methods & variable it is only accessible within the same class.
ACCESS MODIFIERS
Vikas Rajput
Vikas Rajput
@vikasrajputin
Ultimate Backend Development Roadmap in 2022:

📂Basics
📄Internet
📄Client-Server Architecture
📂Any Language & Framework
📄Java + Spring
📄Python + Django
📄JS + Node
📂Git
📂SQL/NoSQL
📂Basic DevOps
📄CI/CD, Cloud Hosting (AWS, etc)
📄Docker, Kubernetes
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Vikas Rajput
Vikas Rajput
@vikasrajputin
Java: Why do we use getter and setter methods?

a thread...

In Java classes, we normally create the getter and setter methods to read and update class level fields respectively.

Let's find out why do we following this practice.

Consider a class "Account", having fields like accountName and accountBalance - to show the name and balance of the account.

As a common practice, both the variables are private and define the public getter and setter method to read and write their values.

Eg:


Using the above example, let's see different use-cases where having getter and setter methods can be game-changing.

1. Validation:

The public getter and setter method act as a single door to access the private fields.

Before updating the value we can run any validation in the setter method and accordingly allow field modification.

Eg:
GETTERSANDSETTERS
Vikas Rajput
Vikas Rajput
@vikasrajputin
Java: Beginner Guide to Multithreading

a thread...

Multithreading is a concept of applying multitasking in Java.

Java supports thread-based multitasking.

Java program can be divided into several threads and those threads can be executed in parallel to support multi-tasking.

Two ways to create a thread in Java:

1. By Implementing Runnable Interface
2. By extending the Thread class

Let's create a thread by implementing the "Runnable" interface:

Steps:
1. Implement Runnable Interface
2. Override the run() method, and put your code inside it.
3. Pass the instance of your class to the Thread class constructor.
4. Call the start() method to run your thread.


Let's create a thread by extending the "Thread" class:

Steps:
1. Extend your class with Thread class
2. Override the run() method, and put your code inside it.
3. Instantiate your class.
4. Call the start() method to run your thread.
MULTITHREADING
Vikas Rajput
Vikas Rajput
@vikasrajputin
Five Different Ways to Create Objects in Java

a thread...

1. Using a new keyword.

It's the most popular one. We create an object by using a new operator followed by a constructor call.

Eg:


2. Using the newInstance() method of class "Class":

Eg:


3️. Using the newInstance() method in class "Constructor":

Eg:


Note:

Both the above ways (Shown in 2 and 3),
are known as reflective ways of creating objects.

Fun-fact:

Class's newInstance() method internally uses Constructor's newInstance() method.
CREATIONOBJECTJAVA

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