How to Compile and Run your first Java Program?

High-level languages like Java, C, C++, etc. compile a program to its equivalent low-level code which can be understood and executed by the machine. In this blog, we will discuss how to write, compile and run a java program.

The first step is to create a folder, create a Java Class and write a Java Program. When we write a Java program, javac (Java Compiler) translates the java source code to the bytecode i.e. .class file. Bytecode is machine language of the Java Virtual Machine (JVM). Bytecode is also referred to as the magic code of Java which is the platform-independent.

An important step after installing Java into the system is to set a path. You can refer to this ‘How to set a path in Java?’ article to know the exact procedure. 

Let’s create a simple java program. 

Create a java file as HelloWorld.java

public class HelloWorld {
	public static void main(String args[]) {
		System.out.println("Hello World");
	}
}

To compile this program type the command shown below on your command prompt and press enter.

javac HelloWorld.java

This runs javac.exe, the compiler. The generalized command to compile any Java program.

javac <Java_file_name>.java

Once you hit enter, the HelloWorld .class file will be generated. You will find both HelloTesters.java and HelloTesters.class among the files in your working directory.

When we compile java program using javac tool, generally java compiler performs below steps:

• Syntax checking

• Adding extra code

• Converting source code to byte code i.e. from .java file to .class file

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So, when I say compiler adds extra code at the time of compilation, for instance, if you have not written any constructor into your program then the compiler will add one default constructor to your program.

So the main purpose of the java compilation is to produce .class file of a program which the machine understands.

Note: Java requires each class placed in its own source file must be same as class name with extension Java. 

When we start compiling the source code, each class is placed in its own .class file that contains bytecode. Suppose, if you want to compile multiple Java files at a time, then you can use below command:

javac *.java

This command will convert all java files to .class file.

With this, we come to an end of this article on the Java Compilation process. I hope you understood how to compile a java program and are clear about each and every aspect that I have discussed above.

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