Java is a rapidly growing programming language amongst developers. Even as one of the oldest languages, it is still a required skill for most software development jobs. One of the reasons being that it can be used for both frontend and backend development. Also, Java is considered to be a ‘write once run everywhere’. In other words, a Java program that is run and compiled in a given environment can be run on other computers irrespective of its architecture or host operating system. The figure below shows how Java stands with other programming languages based on TIOBE’s index. 

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Notice that Java (in green) has continually maintained a top spot for many years and still does. So yes, learning Java looks like a good programming language decision. However, if you are looking to become a Java developer, there is a wide range of things to study. Perhaps, the end goal is that you master everything. This is certainly not what you need to do before you say you are job-ready, as Java can be perceived as complicated yet broad. Amongst the plethora of concepts in Java, some stand out to be critically important. 

More often than not, interview questions stem from these core concepts. It would be wise therefore to ensure you master them as it would not only boost your learning rate but also help you crack interviews. 

In this article, you will discover what these concepts are, get an intuition on what they are about, and understand why you need to learn them. Meanwhile, if you wish to get an in-depth understanding of these concepts, you should consider enrolling in an online Java certification course. Without further ado, let’s blast off. 

The fundamentals of Java

You must understand some of the fundamentals of Java. For instance, what data types are, control flow, conditional statements, etc. These form the basics of Java. You’d be surprised about how for loops and if statements can write powerful codes. Also, it is critical to know the different kinds of data types, strings, int, floats, boolean, long, short, etc. You should know when to use long or short when to use a list or set and so on.

Data structures and Algorithms

Data structures and algorithms are arguably the most important concept to understand as a programmer. By definition, data structures are entities that allow you to store data. Algorithms on the other hand are processes that allow you to manipulate the data and produce a desired result. Every code you write in Java involves data structures and algorithms. The knowledge of these concepts gives you to make an informed decision on which method is most efficient to perform a given task. You also get an intuition as to whether your code will scale well; a key consideration if you are building a project for a business or startup. 

Not using the right data structures and algorithms can cripple your code at some point – rendering all your effort useless. This is why employers are keen on ensuring that you understand data structures and algorithms. 

Object-Oriented Programming

Java is an object-oriented programming language. In other words, virtually everything is an object – just the way we were taught in high school physics that everything can be called a body. In order to write strong Java codes, you need to understand OOP. But what exactly is an object? An object is an instance of a Java class, characterized by three major things: an identity, a state, and a behavior

Let me give a real-world illustration. A motor car can be seen as an object. While there are various cars, a car is known to be a four-wheeled entity (state) that can move from one place to another (behavior) and has a location that is uniquely identified from every other car in the universe (identity). 

In Java, an object has arguments that define its state, a function that defines its behavior, and a memory location that defines its identity

Understanding OOP generally enables you to write better codes. Codes that are generally reusable and can be built upon. In a nutshell, OOP results in cleaner and more efficient codes. 

Multithreading and Multiprocessing 

Multithreading is a technique in Java where more than one block of code can run concurrently. This saves a lot of time especially in cases where there is a delay between output and input. Let’s say you want to perform two separate computations and print the result. Normally, Java runs the first block of code successfully before beginning the second, taking a lot more time to complete. With multithreading, the second code can run while the first is still running. This saves a lot of computational time and makes your code more efficient. 

Multiprocessing is an extension of multithreading. Sometimes, the computing power of your machine may not be able to simultaneously process various information. In such cases, multithreading is of no use. Multiprocessing involves the use of more than one processor running simultaneously to augment the computing power of your machine. 

These two terms are vital concepts in Java and are typically asked in Java interviews. 

Regular Expressions

Regular expressions are an important concept in Java. It allows you to search for and retrieve patterns in a corpus. This is very important when you are particular about the format of the input you’d be getting from a user. Take, for instance, you want to ensure that a user enters a strong password that contains an uppercase letter, a lower case letter, punctuations, and numbers. Regular expressions allow you to write such commands. Typically, it is also used in building local search engines. For instance, find all emails or phone numbers in a text. 

Some common networking protocols 

Let’s face it. As a Java developer, you’d be building applications that would be accessed via the internet. It is thus critical to understand how the internet works and some popular network protocols such as File Transfer Protocol (FTP), Simple mail transport Protocol (SMTP), HyperText Transfer Protocol Secure (HTTPS), HyperText Transfer Protocol (HTTP), and so on. Protocols are defined rules by which computers send and receive information. You can literally impress your hiring manager by demonstrating that you have a decent knowledge of this field. 

Wrapping up

We have seen some concepts that are important when preparing for a Java interview. The list is inexhaustible as there are other worthy mentions such as XML processing, JUnit, GOF design patterns, garbage collection, java collection frameworks, working with date and time, Java best practices, and so on. If you are looking to learn all this, check out for a reputable online Java training.