The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
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.
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:
PATH
environment variable and select it. Click Edit. If the PATH
environment variable does not exist, click New
.PATH
environment variable. Click OK. Close all remaining windows by clicking OK.PATH
environment variable and select it. Click Edit. If the PATH
environment variable does not exist, click New
.PATH
environment variable. Click OK. Close all remaining windows by clicking OK.PATH
environment variable and select it. Click Edit. If the PATH
environment variable does not exist, click New
.PATH
environment variable. Click OK. Close all remaining windows by clicking OK.PATH
environment variable similar to the following when editing it from the Control Panel:
%JAVA_HOME%\bin;%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem
%
) 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):
echo %SystemRoot%
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:
% java -version
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:
For C shell (csh
):
% source ~/.cshrc % java -version
For ksh
, bash
, or sh
:
% . /.profile % java -version
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:
C:> echo %CLASSPATH%
On Solaris or Linux, execute the following:
% echo $CLASSPATH
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.