How to set the Java classpath

by Larry Arnoldy

These classes must first be installed on your PC. Use How to Install the Predefined Wu Classes for instructions on downloading and installing these classes to your PC. Make sure you have noted the exact location on your PC where you installed these files. This location will be needed in Steps 7 and 8 below.

Click the Windows Start button and then Control Panel in the box which appears.

The dialog box below has an area in the top half for user defined environment variables. The bottom half is for maintaining and viewing the values of Windows system environment variables. Click on the upper New to define a new variable, namely the classpath.

In the Variable name field, enter the word classpath. This is the name of the new environment variable. In the Variable value field, enter .; (a dot and a semicolon). Do not press OK yet. The classpath is a list of file and directory locations separated by semicolons. The dot is the symbol for the current directory. If there is no classpath variable defined, Java will simply use the classes in the current directory and Java's own built in classes. If a classpath variable is defined, Java will not use the current directory unless it is included in the value of classpath. Therefore we start with a dot. In the next step we will add one of Wu's predefined packages.

One of the predefined packages from the Wu textbook is the javabook package. It is in the file javabookEd3.zip. Zip files can also be used in the classpath. Here is the hard part: You must know exactly its location on your PC. On my PC it is located at D:\Data\00-UMUC-Wu-Java\WuClasses\javabookEd3.zip . Your location will probably be different, but the end part must be javabookEd3.zip . Enter the full value of the location in the Variable value field after the dot semicolon. Be sure to use the same upper and lower case values that your file explorer shows. Do not click on OK yet. We need to add another value to the classpath.

After javabookEd3.zip enter a semicolon and then the full directory location of the directory in which the galapagos directory is located. Do not include the name of the galapagos directory. On my PC, the galapagos directory is located in the directory D:\Data\00-UMUC-Wu-Java\WuClasses. Add this path to the end of the existing value for classpath. Do not forget the semicolon to separate this value from the previous. Do not include the galapagos directory.

On my PC the full classpath is the following.

.;D:\Data\00-UMUC-Wu-Java\WuClasses\javabookEd3.zip;D:\Data\00-UMUC-Wu-Java\WuClasses

Yours will be different if you put javabookEd3.zip and galapagos in different directories.

You can now see the (start of the) classpath variable in the upper display window. Click on OK until the last dialog box closes. If you later wish to change the classpath, follow the same procedure, but highlight the classpath line and then click on Edit.

You will most likely have to exit your Java editing environment, (DOS window, jGrasp, Textpad, or whatever) in order to make the new classpath available to Java.

You should now be able to use class from the javabook or galapagos packages in your Java applications. You must also include an import statement at the beginning of your source code. You only need the import statement for the package that your application needs. If you were going to use only classes from the javabook package and none from the galapagos project, then it would only be necessary to include the javabook line below.

// Beginning comments import javabook.*; import galapagos.*; // rest of program code

The classpath must contain the exact location of the predefined class on your PC. The import statement must also be correct.  If you mistype either one or made any other mistake with them, you will see errors similar to those below. In that case check the values of the classpath and import statements. Correct them as needed, and try again.

----jGRASP exec: javac -g D:\Data\00-UMUC-Wu-Java\Wu-Stuff\Solutions\Ch02\Exercise2_23.java         Exercise2_23.java:11: package galapagos does not exist     import galapagos.*;     ^     Exercise2_23.java:17: cannot resolve symbol     symbol  : class Turtle     location: class Exercise2_23         Turtle turtle;             ^     Exercise2_23.java:18: cannot resolve symbol     symbol  : class Turtle     location: class Exercise2_23         turtle = new Turtle();                          ^     3 errors