4. Access from a Different Class within a package

A java program may consist of a number of packages.
A package may have a number of classes. For the time being, our program is made of only one package, which is nameless package.

Access Control is to control access to a member in a class. The control is given on two stages. One is on a class. The other is on a member.

This access control is provided by giving access modifiers to member and to class. For a class there are two kinds of modifier, public or no-modifier. For a member, there are four modifiers, public, no-modifier, protected and private. For the time being, we do not consider protected.

To access to a member in a class from other packages, both of class and member must be public. Access to a public member in a public class is always possible. It is possible from anywhere.

To access to a member in a class from a different class in the same package, class and member must be either with public or no-modifier. Access to a member in a class from within the same class is always possible. This means that to prohibit access to a member in a class from a different class, the member must be private.

Here is a sample program to demonstrate the access control.
B.java

class A{
	public int X;
	private int Y;
	void setY(int yy) {
		Y=yy;
	}
	void show(){
		System.out.println("X=" + X + "Y="+Y);
	}
}
class B{
	public static void main(String args[]) {
		A a1=new A();
		a1.X=1;
		//a1.Y=2;
		a1.setY(2);
		a1.show();
	}
}
/*
X=1Y=2
Since X in A is public, a1.X=1 is possible.
But Y in A is private, so a1.Y=2 is not allowed.
Therefore void setY(int yy) is made to set Y in A. 
*/

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