Java Package Class Path and Access protection

How to Set the Class Path:

The classpath is a user defined environment variable that is used by Java to determine where predefined classes are located. It tells the java tools and applications where to find user-defined classes. The syntax to set the classpath is shown as:

C:> set CLASSPATH=%classpath%;classpath1;classpath2.....

You can set multiple path entries that are separated by semi-colons.
To make this thing more understandable, let's put the "HelloWorld" class along with its package "mypackage" under the "C:\mainpackage" directory. Thus the directory structure for this package is shown as:




Now we have changed the location of the package from C:\mypackage\HelloWorld.java to C:\mainpackage\mypackage\HelloWorld.java. Then the CLASSPATH  needs to be changed to point the new location of the package mypackage accordingly shown as:

set CLASSPATH = .;C:\mainpackage;

Although in such condition, Java will look for java classes from the current directory instead of the "C:\mainpackage" directory.


Access protection in packages:

Access protection	Discription
No modifier (default)	The classes and members specified in the same package are accessible to all the classes inside the same package.
public	The classes, methods and member variables under this specifier can be accessed from anywhere.
protected	The classes, methods and member variables under this modifier are accessible by all subclasses, and accessible by code in same package.
private	The methods and member variables are accessible only inside the class.

Access to fields in Java at a Glance:

Access By	public	protected	default	private
The class itself	Yes	Yes	Yes	Yes
A subclass in same package	Yes	Yes	Yes	No
Non sub-class in the same package	Yes	Yes	Yes	No
A subclass in other package	Yes	Yes	No	No
Non subclass in other package	Yes	No	No	No