Run java class windows

java command examples

In this Java tools tutorial, I will guide you how to use the java command provided in JDK (Java Development Kit) to execute Java programs.

Table of content:

java command syntax:

java [options] file.class [arguments. ]

java [options] -jar file.jar [arguments. ]

The first syntax is for executing a class file, and the second one is for executing a JAR file.

Type java -help to consult the available options or browse Oracle’s Java documentation for detailed description and explanation of the options. The arguments, if specified, will be passed into the running program.

• • A Java class must have the public static void main(String[] args) method in order to be executed by the Java launcher.
  • An executable JAR file must specify the startup class in by the Main-Class header in its manifest file.

  1. Run a Java program from a .class file

  If you have a source file called MyProgram.java and it is compiled into MyProgram.class file, type the following command:

  If the class MyProgram.java is declared in the package net.codejava , change the working directory so that it is parent of the net\codejava directory, then type:

  java net.codejava.MyProgram

  If we have a JavaMail-based program that depends on mail.jar library. Assuming the jar file is at the same directory as the class file, type:

  java -cp mail.jar;. PlainTextEmailSender

  NOTES: There must be a dot (.) after the semicolon. If the jar file is inside a directory called lib :

  java -cp lib/mail.jar;. PlainTextEmailSender

  java -cp mail.jar;anotherlib.jar;. MyProgram

  The following example passes two arguments “code” and “java” into the MyProgram:

  If the argument has spaces, we must enclose it in double quotes, for example:

  java MyProgram "code java" 2013

  That will pass two arguments “code java” and “2013”.

  2. Run a Java program from an executable JAR file

  Here the MyApp.jar file must define the main class in the header Main-Class of its manifest file MANIFEST.MF . The header is usually created by the jar tool.

  NOTES: if the jar file depends on other jar files, the reference jar files must be specified in the header Class-Path of the jar’s manifest file. The -cp option will be ignored when using -jar flag.

  Pass two arguments “code” and “java” to the program:

  java -jar MyApp.jar code java

  If the argument contains space, enclose it in double quotes like this:

  java -jar MyApp.jar "code java" 2013

  3. Specify splash screen

  For Swing-based application, we can use the -splash:imagePath flag to show a splash screen at program’s startup. For example:

  java -splash:SplashScreen.png MyProgram

  Here the image SplashScreen.png is loaded as splash screen at startup.

  4. Set system properties

  We can use the -Dproperty=value option to specify a system property when running a program:

  java -Dupload.dir=D:\Uploads MyProgram

  if the property’s value contains spaces, enclose it in double quotes:

  java -Dupload.dir="D:\My Uploads" MyProgram

  java -Dupload.dir=D:\Uploads -Ddownload.dir=D:\Downloads MyProgram

  We can override the predefined system properties. For example, the following command overrides the system property java.io.tmpdir :

  java -Djava.io.tmpdir=E:\Temp MyProgram

  5. Specify memory size

  java -Xms32M -Xmx1024M MyProgram

  Other Java Tools Tutorials:

  About the Author:

  

  Nam Ha Minh is certified Java programmer (SCJP and SCWCD). He started programming with Java in the time of Java 1.4 and has been falling in love with Java since then. Make friend with him on Facebook and watch his Java videos you YouTube.

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  How to Execute and Run Java Code from the Terminal

  

  Md. Fahim Bin Amin

  

  If you work with Java, you’ve probably used one of the well known text editors like Sublime Text, VS Code, Brackets, Atom, and Notepad++ as well as IDEs like Apache NetBeans and IntelliJ IDEA.

  Running code in your IDE is straightforward, but you don’t often get to see how it executes your code (even though you can check the command in the terminal of course!).

  However, it is good practice to know how your code actually executes and provides the output it gives you.

  Many of you might have heard that experienced professional programmers also use the terminal to execute the programs. This gives them better clarity and helps them understand how the code is working, where it is returning the desired value, where the bug might be, and so on.

  Whatever your purpose may be, executing Java code directly from the terminal is a very easy task.

  In this article, I will show you how you can execute Java directly from your favorite terminal window. Fear not! The procedure is quite easy, and after reading the entire article you should be able to run your own Java code in the terminal.

  How to Run Java Code in the Terminal

  The process I am going to show you in this article is applicable to any operating system whether that is Windows, MacOS, or Linux.

  I will be using the following Java code in the next step.

  📦 Step 1 – Go to the directory where your source code is

  If you have already written your Java code in an editor, then simply go into that directory. You can go straight into the directory through your file manager if you want.

  How to go into the directory where the source code is: for Windows 🪟

  Suppose I have the source code ( Main.java ) inside This PC > Documents folder. I can simply go there through my file explorer.

  

  Or, if I want, I can also go there using my terminal. I need to use cd to indicate that I want to change directory.

  In this case, I can use cd «C:\Users\Md. Fahim Bin Amin\Documents» . As my user name contains white spaces, I have used » » to enclose them.

  Then if I check all the files under that directory, then I will get the Main.java file as well.

  I placed the Main.java file under my D drive this time. So I went in that directory using the cd command.

  

  I get my Java file in the terminal as well.

  How to go into the directory where the source code is: for Linux 🐧

  You can go into the directory where you have kept your source code either by following the typical GUI way or from the terminal using the cd command as well.

  

  🧑‍💻How to Compile the Java Code

  Before running our Java code, we need to compile it first. To compile a Java code/program, we get the class file. Then we need to execute/run the class file.

  How to compile Java code using the terminal

  We need to use the command javac file_name_with_the_extension . For example, as I want to compile my Main.java , I will use the command javac Main.java . The c in javac indicates compile.

  

  If the compilation process is successful, then we will not get any errors.

  

  This will create the class file we need under the same directory.

  

  Keep in mind that we run the class file, not the .java file.

  The same process is applicable for all of the operating systems out there.

  

  🖥️ How to Run the Java Code

  We run the .class file to execute the Java programs. For that, we use the command java class_file_name_without_the_extension . Like, as our .class file for this is Main.class , our command will be java Main .

  

  The Java program has been executed successfully!

  The exact same procedure is also applicable for the other operating systems as well.

  

  🏅Bonus: How to Run a Java Program with Packages

  A package basically means a folder. Earlier, I showed you how to use any regular Java code using the terminal. There, I did not use any packages inside the Java code.

  Now I will show you how you can run any Java code that has packages declared within it. This time, I will be using the following Java code.

  package myJavaProgram.Source; public class Main < public static void main(String[] args) < System.out.println("Hello, World!"); >>

  In the first line, I have written the package as package myJavaProgram.Source . This indicates that I want to create a folder named myJavaProgram . Then, I want to create another folder under that named Source . Finally, I want to create the class file of my Java code inside the Source folder.

  The directory tree looks like this: myJavaProgram > Source.

  For compiling this type of Java code with the packages, we use the command javac -d . file_name_with_the_extension .

  As for now, I am using the Main.java file, so I will apply the command javac -d . Main.java . This will create a folder named myJavaProgram, then create another folder named Source under the myJavaProgram folder under the directory where my source file is now.

  

  • The_Directory_Where_I_Have_Kept_My_Source_Code
    • myJavaProgram folder
      • Source folder

  It instantly creates the myJavaProgram folder.

  

  Within the folder, it creates the Source folder.

  

  Inside the Source folder, it creates our .class file. We need this file to run the Java program.

  

  Now if we want to run the .class file, then we need to change the command a little, as we need to provide the directory of the .class file in the terminal window.

  We use the command to run the Java program with packages, java directory_of_the_class_file.the_class_file_name_without_the_extension .

  As I am using Main.java and I need to run the Main.class file, my command will be java myJavaProgram.Source.Main . It will run the Java code like below.

  

  If you’re wondering why we are changing the command now, it’s because earlier, we did not declare any packages. So the Java compiler created the .class file within the directory where our source code was. So, we could get the .class file directly from there and execute the class file as well.

  But if we declare packages inside the source code like this, then we are telling the compiler to create the .class file in another place (not within the directory where our source code currently is). This means that we do not get the class file directly there.

  As we want to run the class file, we need to tell the compiler explicitly where the class file currently is so that it can get the class file and execute it.

  If you think that you might mess up this step, then you can copy the directory directly from your Java code.

  

  In line 1, we have declared the package directory (where we want the class file to be generated). So if we simply copy the directory and add the .class file name without the extension ( .class ) later with a period ( . ), then it satisfies the condition for executing any Java code that has packages declared in the source code.

  The same process is also applicable for the other operating systems as well. I am providing screenshots from a Linux OS here:

  

  Great job! 👏 You can now run any Java code/programs directly using a terminal. 🥳

  I have also created a video where I have shown all the processes mentioned above. You can check that out here. 😁

  💁‍♂️ Conclusion

  I hope this article helps you run your Java programs just using the terminal.

  ➡️ If you want to know how to install a Java compiler for your Windows operating system, then you can check out this article.

  ➡️ If you want to know how to install C and C++ compilers for your Windows operating system, then you can check out this article.

  ➡️ If you want to know how to install Python on your Windows OS, then you can check out this article.

  Thanks for reading the entire article. If it helps you then you can also check out other articles of mine at freeCodeCamp.

  If you want to get in touch with me, then you can do so using Twitter, LinkedIn, and GitHub.

  You can also SUBSCRIBE to my YouTube channel (Code With FahimFBA) if you want to learn various kinds of programming languages with a lot of practical examples regularly.

  If you want to check out my highlights, then you can do so at my Polywork timeline.

  You can also visit my website to learn more about me and what I’m working on.

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  Run Java .Class Files From Command Line

  

  Executing a Java class file from the command prompt is an easy process; make sure you have installed the JDK and follow the process mentioned in this article. This tutorial demonstrates how to execute Java class files from the command line.

  Execute Java Class From the Command Line

  Java class files are compiled Java files that the Java Virtual Machine executes. Let’s try to run the following Java class through the command prompt.

  package delftstack;  public class Demo   public static void main(String[] args)   System.out.println("Hello! This is demo.class example from Delftstack.");  >  > 

  Follow the steps one by one:

  To execute the .java class files, open the Windows command prompt or the macOS terminal.

  

  Go to the Demo.java file directory or any directory where you want to run a Java file.

  

  Run javac , in our case javac Demo.java .

  

  The next step is to run the class; enter java Demo.java in the command prompt; this should output:

  Hello! This is demo.class example from Delftstack. 

  

Sheeraz is a Doctorate fellow in Computer Science at Northwestern Polytechnical University, Xian, China. He has 7 years of Software Development experience in AI, Web, Database, and Desktop technologies. He writes tutorials in Java, PHP, Python, GoLang, R, etc., to help beginners learn the field of Computer Science.

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