Command line execution in Java

Introduction

Command line execution lets you run your Java programs by typing commands. It helps you test and use your programs outside of an editor.

You want to run a Java program you wrote without using an IDE.

You need to test small Java programs quickly.

You want to share your program with others who can run it from their terminal.

You are learning Java and want to understand how programs run.

You want to automate running Java programs in scripts.

Syntax

Java

javac FileName.java
java FileName

javac compiles your Java code into bytecode.

java runs the compiled bytecode.

Examples

Compile and run a simple program named HelloWorld.java.

Java

javac HelloWorld.java
java HelloWorld

Run MyProgram with two command line arguments arg1 and arg2.

Java

javac MyProgram.java
java MyProgram arg1 arg2

Sample Program

This program prints "Hello, world!" to the screen. You compile it with javac HelloWorld.java and run it with java HelloWorld.

Java

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

Important Notes

Make sure your file name matches the public class name exactly, including capitalization.

Run the java command without the .class extension.

If you get errors, check your Java installation and your current folder.

Summary

Use javac to compile Java files.

Use java to run compiled programs.

Command line execution helps you run Java programs outside an editor.