What is PATH and CLASSPATH in Java? Path vs ClassPath Example

What is PATH and CLASSPATH in Java
The PATH and CLASSPATH are the two most important environment variables of the Java environment which are used to find the JDK binaries used to compile and run Java in windows and Linux and class files which are compiled Java bytecodes. From my personal experience I can say that PATH and CLASSPATH are the two most problematic things for beginners in Java programming language due to two reasons; first because in most Java courses nobody tells details of what is a PATH and CLASSPATH, What do PATH and CLASSPATH do, What is meaning of setting PATH and CLASSPATH, What happens if we do not set them, Difference between PATH vs CLASSPATH in Java or simply How Classpath works in Java, etc. 

These basic question which answers most of the details about PATH and CLASSPATH in Java are mostly not answered until Java programmer itself acquire this knowledge, Things may be changed nowadays but important of PATH and CLASSPATH is still high. 

The most common cause of dreaded error like java.lang.NoClassDefFoundError and java.lang.ClassNotFoundException is either incorrect or misconfigured CLASSPATH in Java.

In this article, I'll tell you about the practical difference between PATH and CLASSPATH environment variables, where are they located, and how exactly they are used by the Java compiler and JVM. Once you know this basic detail, you would be able to solve most of the classpath-related problems by yourself.

Difference between PATH and CLASSPATH in Java

Here are some of the common differences between PATH vs CLASSPATH in Java :

1. The main difference between PATH and CLASSPATH is that  PATH is an environment variable that is used to locate JDK binaries like the "java" or "javac" command used to run java program and compile the java source file. On the other hand, CLASSPATH, an environment variable is used by System or Application ClassLoader to locate and load compile Java bytecodes stored in the .class file.

2.  In order to set PATH in Java, you need to include JDK_HOME/bin directory in PATH environment variable while in order to set CLASSPATH in Java you need to include all those directories where you have put either your .class file or JAR file which is required by your Java application.

3. Another significant difference between PATH and CLASSPATH is that PATH can not be overridden by any Java settings but CLASSPATH can be overridden by providing command-line option -classpath or -cp to both "java" and "javac" commands or by using Class-Path attribute in Manifest file inside JAR archive.

4. PATH environment variable is used by the operating system to find any binary or command typed in the shell, this is true for both Windows and Linux environments while CLASSPATH is only used by Java ClassLoaders to load class files.

These were some notable differences between PATH vs CLASSPATH in Java and they are worth remembering to debug and troubleshoot Java-related issues. Though, I highly recommend you to join these best Java Programming courses to build your fundamentals in Java.

How to set PATH and CLASSPATH in Windows and Unix?

If you are familiar with DOS operating system and how to use command prompt in Windows or shell in Linux setting PATH and CLASSPATH is a trivial exercise. Both PATH and CLASSPATH are environment variables and can be set using the export command in Linux and using set keyword in DOS and Windows as shown below:

Command to set PATH in Windows

set PATH=%PATH%;C:\Program Files\Java\JDK1.6.20\bin

Command to set PATH in UNIX/Linux

export PATH = ${PATH}:/opt/Java/JDK1.6.18/bin

Look at the difference between the two commands, in Linux use a colon(:) as a separator, and Windows uses a semi-colon(;) as a separator.

Command to set CLASSPATH in windows

set CLASSPATH=%CLASSPATH%;C:\Program Files\Java\JDK1.6.20\lib

Command to set CLASSPATH in Unix/Linux

export CLASSPATH= ${CLASSPATH}:/opt/Java/JDK1.6.18/lib


Also, don't forget to include the current directory, denoted by a dot(.) to include in CLASSPATH, this will ensure that it will look first in the current directory and if it found the class it will use that even if that class also exists in another directory which exists in CLASSPATH. 

If you using Windows 8 or Windows 10 then you can also follow the steps given here in this article to set up the JAVA_HOME, PATH, and CLASSPATH for Java programs.

It will look something like this in Windows 10 Operating System :

In short, PATH is used by operating system to find the Java binaries. For example, when you type "java" in command line then OS search for java.exe or equivalent Linux executable to execute the Java runtime. On the other hand, Classpath is used to locate the class files which your Java program need. If any class is not find in the Classpath then ClassNotFoundException or NoClassDefFoundError is thrown. 


Other Java setup related articles for beginners:

• How to set PATH in Mac OS X 10.10 Yosemite? (guide)
• How to fix 'javac' is not recognized as an internal or external command? (solution)
• How to set the JAVA_HOME environment variable in Java? (guide)
• How to set java.library.path  in Eclipse IDE (guide)
• How to run a HelloWorld Java program from command prompt (guide)
• How to debug a Java program in Eclipse IDE (guide)

Thanks for reading this article so far. If you found my explanation of PATH and ClassPath useful and you are able to understand the difference between PATH and Classpath then please share this tutorial with your friends and colleagues. If you have any questions, feel free to ask.