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Java Classpath

Learn how to set classpath in Java either as an environment variable and pass as the command-line argument. During runtime of any Java application, the CLASSPATH is a parameter that tells the JVM where to look for classes and packages.

• The default value of the classpath is “ . ” (dot) , meaning that only the current directory is searched for dependencies.
• Specifying either the CLASSPATH environment variable or the -cp command line switch overrides this value.
• The order in which you specify multiple classpath entries is important. The Java interpreter will look for classes in the directories in the order they appear in the classpath variable.

Java Classpath separators are OS specific.

Windows – ; [Semicolon]Linux/Unix – : [Colon]

1. Setting CLASSPATH as Environment Variable

When you have set the location of jar files that are always required during the application runtime, then it’s probably best to add them in the machine’s environment variable ‘CLASSPATH’ .

During application runtime, application class loader will always scan the jar files and classes at specified paths in this variable.

To set CLASSPATH environment variable, find the location of user environment variables in your machine and add all paths where Jar files are stored. Use the separator between different two folders, jar files or classes.

You can find the user environment variables window by –

1. From the desktop, right-click the Computer icon.
2. Choose Properties from the context menu.
3. Click the Advanced system settings link.
4. Click Environment Variables. In the section System Variables, find the CLASSPATH environment variable and select it. Click Edit. If the CLASSPATH environment variable does not exist, click New .
5. Add all folders separated with a separator. Click OK. Close all remaining windows by clicking OK.

If you are creating CLASSPATH for the first time, you need to specify the name for the variable name in Windows 10. Use ‘.’ (dot) to denote the current directory.

2. Setting CLASSPATH from Command Line

Use -classpath argument to set classpath from command prompt/console. Use the following command to set the classpath for different requirements.

Let’s say we have a folder named dependency where JAR files and other classes are placed.

2.1. Add a Single Jar in CLASSPATH

Below syntax examples will add single jar file in classpath.

//WINDOWS $ set CLASSPATH=.;C:\dependency\framework.jar //Linux/Unix $ export CLASSPATH=.:/dependency/framework.jar

2.2. Add Multiple Jars in CLASSPATH

Below syntax examples will add more than one jar file in classpath. To do so, simply use the delimiter for your operating system (either ; or : ) as a separator between the locations specified for the CLASSPATH.

To add all JAR files present in a directory, use wildcard character ( ‘*’ ).

//WINDOWS $ set CLASSPATH=C:\dependency\framework.jar;C:\location\otherFramework.jar $ set CLASSPATH=C:\dependency\framework.jar;C:\location\*.jar //Linux/Unix $ export CLASSPATH=/dependency/framework.jar:/location/otherFramework.jar $ export CLASSPATH=/dependency/framework.jar:/location/*.jar

2.3. Add Multiple Classes in CLASSPATH

Many times, you may need to add individual classes in classpath as well. To do so, simply add the folder where classfile is present. e.g. let’s say there are five .class files are present in location folder which you want to include in classpath.

//WINDOWS $ set CLASSPATH=C:\dependency\*;C:\location //Linux/Unix $ export CLASSPATH=/dependency/*:/location

As a best practice, always organize all JAR files and application classes inside one root folder. This may be the workspace for the application.

Please note that subdirectories contained within the CLASSPATH would not be loaded. In order to load files that are contained within subdirectories, those directories and/or files must be explicitly listed in the CLASSPATH.

If your CLASSPATH environment variable was set to a value that is not correct, then you can unset CLASSPATH by specifying an empty value to it.

3. Executing Programs with ‘-classpath’ or ‘-cp’ Option

Apart from setting the classpath to the environment variable, you can pass an additional classpath to Java runtime while launching the application using –classpath option or –cp option.

Use the . (dot) to include the current path in the classpath where the .class file has been generated.

$ javac –classpath C:\dependency\framework.jar MyApp.Java $ java –classpath .;C:\dependency\framework.jar MyApp

4. Print Current CLASSPATH Value

Anytime you wish to verify all path entries in CLASSPATH variable, you can verify using the echo command.

//Windows c:/> echo %CLASSPATH% //Linux/Unix $ echo $CLASSPATH

If CLASSPATH is not set you will get a CLASSPATH: Undefined variable error (Solaris or Linux) console or simply %CLASSPATH% printed in the windows command prompt.

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PATH and CLASSPATH

This section explains how to use the PATH and CLASSPATH environment variables on Microsoft Windows, Solaris, and Linux. Consult the installation instructions included with your installation of the Java Development Kit (JDK) software bundle for current information.

After installing the software, the JDK directory will have the structure shown below.

The bin directory contains both the compiler and the launcher.

Update the PATH Environment Variable (Microsoft Windows)

You can run Java applications just fine without setting the PATH environment variable. Or, you can optionally set it as a convenience.

Set the PATH environment variable if you want to be able to conveniently run the executables ( javac.exe , java.exe , javadoc.exe , and so on) from any directory without having to type the full path of the command. If you do not set the PATH variable, you need to specify the full path to the executable every time you run it, such as:

C:\Java\jdk1.7.0\bin\javac MyClass.java

The PATH environment variable is a series of directories separated by semicolons ( ; ). Microsoft Windows looks for programs in the PATH directories in order, from left to right. You should have only one bin directory for the JDK in the path at a time (those following the first are ignored), so if one is already present, you can update that particular entry.

The following is an example of a PATH environment variable:

C:\Java\jdk1.7.0\bin;C:\Windows\System32\;C:\Windows\;C:\Windows\System32\Wbem

It is useful to set the PATH environment variable permanently so it will persist after rebooting. To make a permanent change to the PATH variable, use the System icon in the Control Panel. The precise procedure varies depending on the version of Windows:

1. Select Start, select Control Panel. double click System, and select the Advanced tab.
2. Click Environment Variables. In the section System Variables, find the PATH environment variable and select it. Click Edit. If the PATH environment variable does not exist, click New .
3. In the Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable. Click OK. Close all remaining windows by clicking OK.

1. From the desktop, right click the My Computer icon.
2. Choose Properties from the context menu.
3. Click the Advanced tab (Advanced system settings link in Vista).
4. Click Environment Variables. In the section System Variables, find the PATH environment variable and select it. Click Edit. If the PATH environment variable does not exist, click New .
5. In the Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable. Click OK. Close all remaining windows by clicking OK.

1. From the desktop, right click the Computer icon.
2. Choose Properties from the context menu.
3. Click the Advanced system settings link.
4. Click Environment Variables. In the section System Variables, find the PATH environment variable and select it. Click Edit. If the PATH environment variable does not exist, click New .
5. In the Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable. Click OK. Close all remaining windows by clicking OK.

Note: You may see a PATH environment variable similar to the following when editing it from the Control Panel:

%JAVA_HOME%\bin;%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem

Variables enclosed in percentage signs ( % ) are existing environment variables. If one of these variables is listed in the Environment Variables window from the Control Panel (such as JAVA_HOME ), then you can edit its value. If it does not appear, then it is a special environment variable that the operating system has defined. For example, SystemRoot is the location of the Microsoft Windows system folder. To obtain the value of a environment variable, enter the following at a command prompt. (This example obtains the value of the SystemRoot environment variable):

Update the PATH Variable (Solaris and Linux)

You can run the JDK just fine without setting the PATH variable, or you can optionally set it as a convenience. However, you should set the path variable if you want to be able to run the executables ( javac , java , javadoc , and so on) from any directory without having to type the full path of the command. If you do not set the PATH variable, you need to specify the full path to the executable every time you run it, such as:

% /usr/local/jdk1.7.0/bin/javac MyClass.java

To find out if the path is properly set, execute:

This will print the version of the java tool, if it can find it. If the version is old or you get the error java: Command not found, then the path is not properly set.

To set the path permanently, set the path in your startup file.

For C shell ( csh ), edit the startup file (~/.cshrc ):

set path=(/usr/local/jdk1.7.0/bin $path)

For bash , edit the startup file ( ~/.bashrc ):

PATH=/usr/local/jdk1.7.0/bin:$PATH export PATH

For ksh , the startup file is named by the environment variable, ENV . To set the path:

PATH=/usr/local/jdk1.7.0/bin:$PATH export PATH

For sh , edit the profile file ( ~/.profile ):

PATH=/usr/local/jdk1.7.0/bin:$PATH export PATH

Then load the startup file and verify that the path is set by repeating the java command:

% source ~/.cshrc % java -version

Checking the CLASSPATH variable (All platforms)

The CLASSPATH variable is one way to tell applications, including the JDK tools, where to look for user classes. (Classes that are part of the JRE, JDK platform, and extensions should be defined through other means, such as the bootstrap class path or the extensions directory.)

The preferred way to specify the class path is by using the -cp command line switch. This allows the CLASSPATH to be set individually for each application without affecting other applications. Setting the CLASSPATH can be tricky and should be performed with care.

The default value of the class path is «.», meaning that only the current directory is searched. Specifying either the CLASSPATH variable or the -cp command line switch overrides this value.

To check whether CLASSPATH is set on Microsoft Windows NT/2000/XP, execute the following:

On Solaris or Linux, execute the following:

If CLASSPATH is not set you will get a CLASSPATH: Undefined variable error (Solaris or Linux) or simply %CLASSPATH% (Microsoft Windows NT/2000/XP).

To modify the CLASSPATH , use the same procedure you used for the PATH variable.

Class path wildcards allow you to include an entire directory of .jar files in the class path without explicitly naming them individually. For more information, including an explanation of class path wildcards, and a detailed description on how to clean up the CLASSPATH environment variable, see the Setting the Class Path technical note.

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