How can I compile a .java file?

What programs will I need? If I need the Java JDK I will also need help installing that. I'm very new to Ubuntu, so any program that I need to install I will need a tutorial on how to install them.


5 Answers 5


To compile the file, open your terminal and type

javac filename.java

To run the generated class file, use

java filename

But to do this you need to have the Java JDK installed in your computer. You can install it with the instructions in How do I install Java?.

  • 1
    umm.. no. javac java_test.java finishes successfully, but there is no java_test file to be found. only a g.class
    – phil294
    Jun 30, 2017 at 1:09
  • @Blauhirn yes, but if you still just run java filename it will work, even though the file is not there. Sep 22, 2017 at 20:23
  • 4
    If javac generates Program.class then run it with java Program
    – spencer.sm
    Aug 26, 2018 at 3:56
  • If someone get a java.lang.ClassNotFoundException, try java -cp . filename. Sep 5, 2019 at 1:07

OpenJDK works best for me. It's simple and I have never faced any problem with it. Just follow these simple steps:

  1. From Terminal install open jdk

    sudo apt-get install openjdk-7-jdk
  2. Write a java program and save the file as filename.java

  3. Now to compile use this command from the terminal

    javac filename.java

    If everything works well then a new "filename.class" file should be created.

  4. To run your program that you've just compiled type the command below in terminal:

    java filename


You can use any text editor (like gedit) ,

replace the filename with watever name you want

you need to be on same directory as the "present working directory" (got by running pwd) while running the command from terminal.

  • 6
    "Error: Could not find or load main class"
    – Dev
    Aug 28, 2018 at 11:54
  • step 4 should be "java [class_name] Apr 16, 2020 at 10:40

If for example your file is my_file.java:

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

You want to do:

javac my_file.java

and then

java MyClass # The name of the class, not file

However, it is a common convention to give classes and files the same name.

  • 1
    I would say your original version was better, since # is the comment character in shells.
    – muru
    Nov 3, 2014 at 1:58

You need to install a JDK, Java Development Kit. Ubuntu contains a metapackage default-jdk, which depends on currently prefered JDK. Now it is openjdk-6-jdk.

To compile a Java file to runnable .class file you can run

javac filename.java

and run it

java file

It is the most simple use-case and mostly it doesn't work because java classes mostly depends on other java classes placed in libraries.

So you would probably like to use some more sophisticated solutions. Most text editors supports Java syntax highlighting, for example jEdit, kate or vim, but they don't solve your compilation issue.

You have another option - you can install a full featured Java IDE. Ubuntu comes with both main OpenSource Java IDEs - NetBeans and Eclipse.

  • For a first installation, default-jdk is a must and openjdk-X-jdk is not enough.
    – JohnRos
    Feb 15, 2014 at 22:35

Just type sudo apt-get update, followed by sudo apt-get install openjdk-7-jdk for a quick installation for java7, then you can play games with java :-)

For more detailed official Java documentation, please visit this link.

  • 2
    I'd suggest that people starting to learn Java now would be best off learning the latest version, Java 7 (sudo apt-get install openjdk-7-jdk). Also, it's best to run sudo apt-get update before installing packages from the Terminal. Jun 3, 2012 at 3:56
  • 7 is only present in 12.04. 6 makes the answer more generic Jun 3, 2012 at 6:39

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