Java classes are usually organized in packages which group together
related classes. The classes in the package are placed under the some
directorory. Related packages are usually organized hierarchically, i.e.,
as directory tree. E.g., class javax.servlet.http.Cookie
is a part of javax.servlet.http package,
and its bytecode resides in the file:
/some/dir/javax/servlet/http/Cookie.class.
If the Cookie class is needed by your Java
application/servlet/applet, you need to either refer to it by its full name:
javax.servlet.http.Cookie or place
an import statement at the top of your source file:
package my.java.utils;
import javax.servlet.http.Cookie;
...
Cookie saveId = new Cookie("User", userId);
But how the
java or
javac
knows where the
/some/dir/javax/servlet/http/Cookie.class is
located? From the
CLASSPATH which either lists
top directories for packages (in example above:
/some/dir) or
jar files.
