Core Java - Part 1

Welcome to the first part of three Core Java tutorials. In this series, we’ll discuss the basics of Core Java with practical examples. So let’s get started.

Java is an object-oriented programming language(OOPS). Sun Microsystems developed it in 1995, and it was later acquired by Oracle. It is secure and platform-independent, which means its compiled programs can be run on any operating system. We can run our Java programs on a wide variety of computers using a range of OS (macOS, Windows, Linux, etc.). This is possible because our Java program doesn’t execute directly on our computers. It runs on a standardized hypothetical computer known as Java Virtual Machine (JVM). This JVM is implemented in our computer by a program called Java interpreter. Don’t get confused by the terminology. We will discuss everything in detail. Let’s start with these terms.

1. Java Virtual Machine (JVM) - It provides a runtime environment in which Java bytecode can be executed.

2. Java Compiler - It compiles the .java file into bytecode. Bytecodes are binary instructions for Java interpreter.

3. Java Interpreter - It reads the bytecode and converts it into machine code.

NOTE - Java is platform-independent, but JVM is not. According to the OS, you need to install it into your machine.

Installation

Go to https://java.com/en/download/ and download the Java development toolkit(JDK) based on your OS.

After installation, set the path variable.

For Windows users, go to System Properties then Environment Variables. In system variable go to path and enter the path to the bin folder inside your JDK in the variable value. Click OK.

You can confirm that you have installed Java by opening the terminal and running javac command.

Compiling a Java Program -

The below command is used to compile a Java program -

javac test.java

javac is the compiler that compiles our program and creates a file with the extension .class The class file contains bytecodes that are binary instructions for Java interpreter.

To run application program -

The command below is used to run a Java program -

java test

• A Java program is a collection of one or more classes. There is at least one class in every program.

• A Java program file must be saved with the .java extension.

• We must save the program file with the same name as that of the class defined within it.

• We must put the code for each public class in a separate file. (There can be only one public class in a file).

We will discuss what a class is and what is public in this series’s later parts.

Variables

A variable is known as a named value holder in primary memory. When a variable is declared, the compiler is able to check that it is not being used in a manner or context that is inappropriate to its type (type checking).

Example - int x = 10; Here x is a variable of integer type. We’ll discuss different data types later.

Variable Names

The name we choose for a variable is called an identifier, and an identifier can be of any length, although it must begin with a letter. The rest of the identifier can include digits. Operators and spaces are not allowed in identifiers. Java variables are case sensitive, which means name and NAME are two different identifiers.

We can’t use Java keywords as a name for something. Keywords are an essential part of the language and are meant for specific purposes.

Below are some examples of valid identifiers -

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2
3
4
max, Max, MAX
ab$123
$ab_123
_abcd

Below are some examples of invalid identifiers -

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7
ab + cd
ab - cd
ab @cd
ab cd
123 abcd
while
final

The last two while and final are reserved keywords.

In general, we follow camel case notation for variables, class, or method names in Java. Below is the example -

HelloWorld, calculateTotal, findMyAge().

That’s all for now for this part. We’ll continue in the next part with DataTypes, Type conversion, and more. Till then, happy coding :)