after surfing the web I realized that I should set the class path the path File of the connecter jar file in system environment variables I did so and in commandline by entering this command I have this:
C:\Users\User>echo %classpath%
D:\classpath\mysql-connector-java-5.1.22-bin.jar
but when I wrote a java program to show me the class path:
System.out.println(System.getProperty("java.class.path"));
it shows me this one:
C:\Users\User\Documents\NetBeansProjects\JavaApplication3\build\classes;C:\Users\User\Documents\NetBeansProjects\JavaApplication3\src
I want to connect to a database how should I install my connector?
The JDBC driver does not need any "installation".
You should not set the system wide CLASSPATH environment variable, that only leads to confusion.
When starting your program, simply provide the location of the file to the Java command:
java -cp myapp.jar;D:\classpath\mysql-connector-java-5.1.22-bin.jar MyMain
To use it inside your NetBeans project, add the jar file in the "Libraries" section of your project.
Just add *D:\classpath* to the CLASSPTH using set command (set CLASSPATH=%CLASSPATH%;D:\classpath;) on the command prompt or by defining a CLASSPATH environment variable using UI.
来源：https://stackoverflow.com/questions/12601879/how-to-install-mysqlconnecter-java-correctly