java Command in Linux

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Java is a high-level programming language commonly used for web application development. It is available and compatible with all major operating systems like Linux, macOS, and Windows. In Linux operating systems, the "java" command is used to run or start a Java application. However, these applications must be compiled, which can be done using the javac command.

Table of Contents

Here is a comprehensive guide to the options available with the java command −

• How Does java Command Work?
• Syntax of java Command
• Options java Command
• How to Check if java Command is Installed?
• How to Use java Command in Linux?

How Does java Command Work?

The java command in Linux allows us to run a compiled Java application. When we execute this command, it initiates the Java Virtual Machine (JVM) in the background, loads the specified class, and invokes the main() method of that class. However, its important to note that the main() method must be declared public and static, must accept a String array as a parameter, and doesnt return any value.

Syntax of java Command

You can use the following syntax to run a Java application from a Linux terminal −

java [ options ] className [ argument ... ]
java [ options ] -jar fileName.jar [ argument ... ]

The first syntax runs a compiled Java class file while the other one executes a Java application packaged in a JAR (Java Archive) file. Here, the options represent command-line options, className is the class to be invoked, and fileName indicates the JAR file that needs to be run. Moreover, the argument represents the arguments to be passed to the main() method.

Options java Command

Linux java command supports several options that are listed in the following table along with the description −

Apart from these options, the java command supports some other options as well. You can access the manual page of the java command to learn more about it and its option −

man java

How to Check if java Command is Installed?

You can verify the existence of the Linux java command by checking its version. If the command shows the Java version. This means Java is installed on your Linux system −

java -version

If Java is not installed on your system, you will encounter a command not found error. In such a case, you can the following command to install Java on your Linux system −

#for Ubuntu or Debian
sudo apt install default-jdk
#for RHEL/CentOS/Fedora
sudo yum install java-11-openjdk
#For Arch Linux
sudo pacman -S jdk-openjdk

How to Use java Command in Linux?

Lets go through the following steps to learn the use of a java command in Linux −

Step 1: Create a Java File

Lets create a simple Java file in any editor like Nano −

nano javaExample.java

Now paste the following code into this file to print a greeting message on the console −

public class ExampleClass{
   public static void main(String[] args) {
      System.out.println("Hi Geeks, Welcome to Tutorialspoint!");
   }
}

Save the file and exit it.

Step 2: Compile the Java File

Now use the javac command to compile the javaExample.java −

javac javaExample.java

This command will create a compiled file with the ".class" extension, as shown below −

Step 3: Run the Java File

Now you can run the compiled Java using the java command, as shown below −

java javaExample.class

On successful execution of this command, you will get the desired output, as follows −

Similarly, you can use the java command to run a JAR file. However, in that case, you must specify the -jar option before the class name, as shown below −

java -jar fileName.jar

Thats all about the use of java command in Linux.

Conclusion

Java is a powerful, high-level programming language that is widely used for web application development across various operating systems, including Linux. The java command is a useful utility for developers that allows them to run compiled Java applications efficiently. The java command initiates the Java Virtual Machine (JVM), loads the specified class, and executes the main() method.

In this tutorial, we covered the basic syntax of the java command, its various options, how to check for Java installation, and provided a step-by-step guide on creating, compiling, and running a Java program in a Linux environment.