Zen Notes
Cogitatio materialis est

How to run java from command line?

10th Nov 2013 Tags: #development #java

This document instructs you on how to use the Linux shell with Java. Let's assume you have already installed Java and have java[c]* commands.

Compile & Run simple program

If you have simple Hello World in current directory,

$ ls
Hello.java

then compiling and runnig is pretty easy:

$ javac Hello.java
$ ls
Hello.class Hello.java
$ java Hello
Hello, Men!

NOTE #1: when you compile the src, include the .java extension!

NOTE #2: be sure to omit a trailing .class extension, when execute a program!

If you get an error during executin like

Exception in thread "main" java.lang.NoClassDefFoundError

try to use

java -cp . Hello

If it succeed, your java-classpath is set incorrectly.

Compile and Run a program with package

If you have a project, or java-file from eclipse with package, there is a small trick:
you should use fully qualified name (with package name and correct directory structure), otherwise you will get an error

Exception in thread "main" java.lang.NoClassDefFoundError: Hello (wrong name: com/bitthinker/Hello)
bla bla blah ...

So, to resolve it, let's assume your Hello.java in inside com.bitthinker pachage, so, you should have the following dir-structure:

/workspace
  /com
    /bitthinker
      Hello.java

Then, the whole trick if you are in workspace folder is (be patient):

$ javac com/bitthinker/Hello.java
$ java  com.bitthinker.Hello
Hello, Man!

For more information, see Useful links section :)

Useful links: