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How to use the apache commons java library on Ubuntu?

I am a Java beginner and trying to figure out how to use the apache commons lib.
Here is a source file Randstr.java:
import org.apache.commons.lang3.RandomStringUtils;
class Randstr {
public static void main(String[] args) {
String s = RandomStringUtils.random(12);
System.out.println(s);
}
}
I have the commons-lang3-3.1.jar file in /usr/share/java/ and have created a symlink in the current dir. Then I compiled it like this: javac -cp commons-lang3-3.1.jar Randstr.java, the complilation was fine, but when I execute java Randstr, I got the following error:
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/lang3/RandomStringUtils
at Randstr.main(Randstr.java:5)
Caused by: java.lang.ClassNotFoundException: org.apache.commons.lang3.RandomStringUtils
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 1 more
And if I don't specify the jar file in the classpath, it will not even compile:
javac -cp . Randstr.java
# Randstr.java:1: error: package org.apache.commons.lang3 does not exist
# import org.apache.commons.lang3.RandomStringUtils;
# ^
# Randstr.java:5: error: cannot find symbol
# String s = RandomStringUtils.random(12);
# ^
# symbol: variable RandomStringUtils
# location: class Randstr
# 2 errors
javac -cp /usr/share/java/ Randstr.java
# Randstr.java:1: error: package org.apache.commons.lang3 does not exist
# import org.apache.commons.lang3.RandomStringUtils;
# ^
# Randstr.java:5: error: cannot find symbol
# String s = RandomStringUtils.random(12);
# ^
# symbol: variable RandomStringUtils
# location: class Randstr
# 2 errors
From reading other questions on stackoverflow, I see this can be solved by using an IDE, but I prefer a simple editor at the moment.

If you can compile it with
javac -cp commons-lang3-3.1.jar Randstr.java
then you can run it with
java -cp commons-lang3-3.1.jar:. Randstr
The JAR file has to be in the classpath.

Edit your profile file. vim ~/.bashrc
In your profile file add the following line:
export CLASSPATH=/usr/share/java/commons-lang3-3.1.jar:.
Log out and back in. Or source your profile file in the windows you have open. You can always add your classpath to every java and javac command you invoke but that becomes a pain. With the CLASSPATH environmental variable you don't have to add it on the command line any more. Note that if you are using an IDE such as NetBeans or Eclipse you still might have to add the library to your project's libraries within the IDE.

Clearly the contents of /usr/share/java/ don't automatically get added to the classpath - it's just a common location where APT packages put Java libraries. It's up the developer to reference them correctly.
JARs in the ext/ subdirectory of a Java installation do get added to the classpath automatically. However, do not put your own JARs in there. It's a terrible practice because it doesn't match how Java apps are deployed "in the real world".
The correct way is using the -cp parameter explicitly when compiling AND running your app. Java doesn't compile library code into your .class files, a .class file only refers to names of other classes which are then loaded as-needed from the class path when your app runs. The -cp parameter takes only .jar files, or directories with .class files in them. You can also use wildcards in the value of that parameter. For more information on wrangling the class path, check the tool documentation on setting the class path.
You using a build tool that sets it for you automatically, like an IDE or Maven or another build system with dependency management. (Gradle or Ant+Ivy.) If you're writing a Java app that uses third party libraries, I very strongly suggest you learn and use one of those. (Also, most IDEs can work with Maven's configuration files letting you use the same build settings in a team with people using mixed or no IDEs.) Generally if you're invoking a compiler directly you're not doing it right.

Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld

I've been working on this for about an hour and thumbing through Q&As on stackoverflow but I haven't found a proposed solution to my problem. I'm sorry if this is a duplicate, but I couldn't find any duplicate question with an answer that solved my specific problem.
I am trying to write and compile a java program from terminal for the first time (up until this point I have been using Eclipse for java and VIM for everything else, but I feel its time to switch entirely to VIM). Here is my current HelloWorld code:
package main;
public class HelloWorld {
public static void main(String args[]) {
System.out.println("Hello World!");
}
}
I compile and run using the following commands (specifying the classpath to ensure that isn't the problem):
javac -cp "./" HelloWorld.java
java -cp "./" HelloWorld
This gives me the following error message:
Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld (wrong name: main/HelloWorld)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:791)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:480)
I know it is seeing the file HelloWorld.class and trying to access the class HelloWorld because if I change the run command to:
java -cp "./" Foo
I get an entirely different error message:
Error: Could not find or load main class Foo
I have tried several dozen pages worth of troubleshooting and come up short, including the following:
Exception in thread "main" java.lang.NoSuchMethodError: main
http://introcs.cs.princeton.edu/java/15inout/mac-cmd.html
java -version yields:
java version "1.7.0_07"
Java(TM) SE Runtime Environment (build 1.7.0_07-b10)
Java HotSpot(TM) Client VM (build 23.3-b01, mixed mode)
My operating system is LinuxMint and uname -a yields:
Linux will-Latitude-D620 2.6.38-8-generic #42-Ubuntu SMP Mon Apr 11 03:31:50 UTC 2011 i686 i686 i386 GNU/Linux

package main;
This means that your class resides in the main package, and its canonical name is main.HelloWorld.
Java requires that package names should also be mirrored in the directory structure. This means that:
Your HelloWorld.java file should be in a directory named main
You should execute javac and java from the directory containing main, not from main itself
The classpath should contain the directory where the main directory is, not main itself
java expects the canonical name of the class to execute, so main.HelloWorld
So, to recap:
You should have something like myproject/main/HelloWorld.java
From myproject, run javac main/HelloWorld.java
From myproject, run java -cp ./ main.HelloWorld

You've put your class in a package named "main", but you're trying to treat it like it isn't in a package. Since you put package main; at the top of your source file, you need to put HelloWorld.java in ./main, then run javac ./main/HelloWorld.java, followed by java -cp . main.HelloWorld.
These commands will get you the working example you're trying to build:
mkdir main
echo 'package main; public class HelloWorld { public static void main(String... args) { System.out.println("Hello World"); } }' > main/HelloWorld.java
javac main/HelloWorld.java
java -cp . main.HelloWorld

As a beginner you might encounter a very similar scenario where the error output is the same. You try to compile and run your simple program(without having any package set) and you do this:
javac HelloWorld.java
java HelloWorld.class
This will give you the same java.lang.NoClassDefFoundError since java thinks HelloWorld is your package and class your class name. To solve it just use
javac HelloWorld.java
java HelloWorld
See the Java page - Lesson: Common Problems (and Their Solutions)

Problem:
Basically, the Exception in thread "main" java.lang.NoClassDefFoundError:
means, that the class which you are trying to run was not found in the classpath.
Solution: you need to add the class or .jar file which contains this class into the java classpath. When you are running a java class from the command line, you need to add the dot (.)
java YourSingleClass -cp .
into the classpath which tells the JVM to search for classes in actual directory.
If you are running a class from a .jar file, you need to add this jar file into the classpath:
java org.somepackage.SomeClass -cp myJarWithSomeClass.jar

ClassNotFoundException despite class in the classpath

The ClassNotFoundException questions are found by the dozens on SO but even so I did not find the answer to my problem in past answers :(
Basically I get a ClassNotFoundException while trying to run a large open source program from the command line using a command prompt that is provided in the project's doc. The prompt is as follow:
java -cp "target/classes/*;../../Algotrader/code/target/classes/*;../../lib/*;../../target/*" -Dsimulation=true -DdataSource.dataSet=1year com.algoTrader.starter.SimulationStarter simulateWithCurrentParams
(note: the original command actually says java.exe but I changed it to java as java.exe is not recognised as a command on my Mac)
The exception is thrown for the SimulationStarter class as shown by the stack trace:
Exception in thread "main" java.lang.NoClassDefFoundError: com/algoTrader/starter/SimulationStarter
Caused by: java.lang.ClassNotFoundException: com.algoTrader.starter.SimulationStarter
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
From Eclipse I can see that SimulationStarter.class is in AlgoTrader/code/target/classes/com/algoTrader/starter, which looks in line with the path provided in the command prompt.
So my question is: what could be the cause(s) for this exception other than the class being incorrectly placed in the classpath?
Also not sure this makes any difference but the project is kept under svn and Maven and I am running it on a Mac.
CORRECT CLASSPATH
In the end the classpath given in the command prompt was at fault. The correct paths (at least ones that solve the problem) are:
java -cp "target/classes/:../../Algotrader/code/target/classes/:target/*" -Dsimulation=true -DdataSource.dataSet=1year com.algoTrader.starter.SimulationStarter simulateWithCurrentParams
The main differences with the original prompt is the removal of the stars except for the folder that contains the jar files and the shortening of the base classpath paths to capture only the base directories. Also ":" should be used instead of ";" on Macs and Linux as per
#reprogrammer answer

Are you sure you need all the * there?
Usually, you will want to give the base directories of the classpath, not subfolders.
E.g. when building your application into "bin", you would use java -cp bin mainclass, not java -cp bin/*! The support for * is generally a bit flaky, as it is a shell metacharacter, and you need to get quoting right. It can really screw you if you have an incorrect classpath. I've seen people have issues because they added README.TXT to their classpath.

The classpath syntax is OS-dependent. The classpath separator in Linux and Mac OS X is : not ;.

running java from command line

I have been mostly using eclipse so far. Now I'm trying to run java from terminal but I have a problem with packages.
This is my Main.java file:
package main;
class Main {
public static void main(String[] args) {
System.out.println("it's working");
}
}
I compile this using javac Main.java and then run with java Main which gives me:
java Main
Exception in thread "main" java.lang.NoClassDefFoundError: Main
Caused by: java.lang.ClassNotFoundException: Main
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
Could not find the main class: Main. Program will exit.
When I remove package Main everything works fine. What am I missing?
java -version gives:
java version "1.6.0_24"
OpenJDK Runtime Environment (IcedTea6 1.11.4) (6b24-1.11.4-1ubuntu0.12.04.1)
OpenJDK 64-Bit Server VM (build 20.0-b12, mixed mode)

You need to run the java command up one directory level and give it in the fully qualified package name, eg: java main.Main
See How the Java Launcher Finds User Classes to learn how this works.

You can use this command:
java main.Main
Make sure the main (lowercase) package directory is on the classpath.

It is possible that your classpath is not set correctly.
Since you gave your .java file a package it is unnamed no longer.
An example:
java -cp ./package1/ main.Main //from the current directory and
//if main package is contained in package1
You need to fully qualify the class name.
For future reference if you want to run from the command line you must stop the indirection (for lack of a better term) at the package level.
Say your class was in the package package1.package2.Main.java
I would run it like so java -cp /blah/blah package1.package2.Main

Compile
Windows:
javac main\Main.java
Mac:
javac main/Main.java
Run
java main.Main

If you add package Main, then you must put your source file in folder Main/Main.java. After that you can compile. When you run the program, go to Main folder using "cd", then write java -cp Main.Main
See my question similiar to yours noclassdeffounderror

try this...
In window , you just compile the code as
javac - d . Main.java
then a package(folder) with the name you specified in your class is created (in your code, package with name "main" is created) in the same path where your program reside...
Then you just run the program as
java main.Main
or
java main/Main

How do I run Java .class files?

I've compiled a HelloWorld program, and I'm using the command prompt to run it. The .class file is named HelloWorld2.class
The file is located in C:\Users\Matt\workspace\HelloWorld2\bin
Here's what I'm getting when I go to command prompt, and type "Java HelloWorld2" :
C:\Users\Matt>Java HelloWorld2
Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld2
Caused by: java.lang.ClassNotFoundException: HelloWorld2
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
Could not find the main class: HelloWorld2. Program will exit.
I was expecting to see a HelloWorld printed out. What am I doing wrong? I have the JDK installed.

If your class does not have a package, you only need to set the classpath to find your compiled class:
java -cp C:\Users\Matt\workspace\HelloWorld2\bin HelloWorld2
If your class has a package, then it needs to be in a directory corresponding to the package name, and the classpath must be set to the root of the directory tree that represents the package.
// Source file HelloWorld2/src/com/example/HelloWorld2.java
package com.example;
...
Compiled class file: HelloWorld2/bin/com/example/HelloWorld2.class
$ java -cp HelloWorld2/bin com.example.HelloWorld2

To run Java class file from the command line, the syntax is:
java -classpath /path/to/jars <packageName>.<MainClassName>
where packageName (usually starts with either com or org) is the folder name where your class file is present.
For example if your main class name is App and Java package name of your app is com.foo.app, then your class file needs to be in com/foo/app folder (separate folder for each dot), so you run your app as:
$ java com.foo.app.App
Note: $ is indicating shell prompt, ignore it when typing
If your class doesn't have any package name defined, simply run as: java App.
If you've any other jar dependencies, make sure you specified your classpath parameter either with -cp/-classpath or using CLASSPATH variable which points to the folder with your jar/war/ear/zip/class files. So on Linux you can prefix the command with: CLASSPATH=/path/to/jars, on Windows you need to add the folder into system variable. If not set, the user class path consists of the current directory (.).
Practical example
Given we've created sample project using Maven as:
$ mvn archetype:generate -DgroupId=com.foo.app -DartifactId=my-app -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false
and we've compiled our project by mvn compile in our my-app/ dir, it'll generate our class file is in target/classes/com/foo/app/App.class.
To run it, we can either specify class path via -cp or going to it directly, check examples below:
$ find . -name "*.class"
./target/classes/com/foo/app/App.class
$ CLASSPATH=target/classes/ java com.foo.app.App
Hello World!
$ java -cp target/classes com.foo.app.App
Hello World!
$ java -classpath .:/path/to/other-jars:target/classes com.foo.app.App
Hello World!
$ cd target/classes && java com.foo.app.App
Hello World!
To double check your class and package name, you can use Java class file disassembler tool, e.g.:
$ javap target/classes/com/foo/app/App.class
Compiled from "App.java"
public class com.foo.app.App {
public com.foo.app.App();
public static void main(java.lang.String[]);
}
Note: javap won't work if the compiled file has been obfuscated.

This can mean a lot of things, but the most common one is that the class contained in the file doesn't have the same name as the file itself. So, check if your class is also called HelloWorld2.

Go to the path where you saved the java file you want to compile.
Replace path by typing cmd and press enter.
Command Prompt Directory will pop up containing the path file like C:/blah/blah/foldercontainJava
Enter javac javafile.java
Press Enter. It will automatically generate java class file