How to compile a .java file on Ubuntu?

  • 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.

  • rɑːdʒɑ

    rɑːdʒɑ Correct answer

    8 years ago

    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?.

    umm.. no. `javac java_test.java` finishes successfully, but there is no `java_test` file to be found. only a `g.class`

    @Blauhirn yes, but if you still just run `java filename` it will work, even though the file is not there.

    If `javac` generates `Program.class` then run it with `java Program`

    If someone get a `java.lang.ClassNotFoundException`, try `java -cp . filename`.

  • 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
      

    NOTE

    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.

    "Error: Could not find or load main class"

    step 4 should be "java [class_name]

  • 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.

    I would say your original version was better, since `#` is the comment character in shells.

  • 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.

  • 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.

    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 `install`ing packages from the Terminal.

    7 is only present in 12.04. 6 makes the answer more generic

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Content dated before 6/26/2020 9:53 AM