How to Run Java Programs in Ubuntu Terminal

If you are new to Linux and have no idea how to set up your system so you can code in Java, then this tutorial is just for you.

To run Java programs in Ubuntu command line, you have to follow 3 simple steps:

1. Install java compiler
2. Compile Java code
3. Run compiled code

Let's start with the installation of the Java compiler.

Step 1: Install the Java compiler

Unlike modern programming languages like Python, in Java, every program must be compiled (the approach is similar to running C programs in Ubuntu).

The first step is to check if you already have it installed or not using the following command:

javac --version

But if it throws you an error, it simply means the Java compiler is not installed and you have to install it manually.

The Java compiler is a part of the JDK (Java Development Kit) which means you need to install the JDK in Ubuntu to get the Java compiler.

To install JDK in Ubuntu, use the following command:

sudo apt install default-jdk

Step 2: Compile the Java program

Once you have the compiler installed, let's have a look at how you can compile a program.

I will be using a simple Hello World:

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

To compile a Java program, you'd have to use the javac command in the following manner:

javac Filename.java

I will be using the Hello.java file, so my command would look like this:

javac Hello.java

After the successful compilation, it will create a class file which is our compiled file and can be found by listing the contents of a directory:

ls

Step 3: Run the compiled Java program

Once you are done with the compilation, finally, you can run the Java file.

To run the compiled Java program, use the Java command along with the class file name (without using the .class extension):

java Filename

Yep, you don't have to specify the .class extension after the filename!

In my case, it looked like this:

There you have it!

Running Java in modern IDEs? Setup JAVA_HOME Variable

If you are running Java programs in modern IDEs like Eclipse, Netbeans, Maven, etc. then it will require you to set up the JAVA_HOME variable.

Want to know how you do it? Here's a detailed guide explaining how to set JAVA_HOME variable in Ubuntu:

How to Set JAVA_HOME Variable in Ubuntu Linux Correctly

If you are running Java programs on Ubuntu using Eclipse, Maven or Netbeans etc, you’ll need to set JAVA_HOME to your path. Otherwise, your system will complain that “java_home environment variable is not set”. In this beginner’s tutorial, I’ll show the steps to correctly set

It's FOSSAbhishek Prakash

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