INHERITANCE AND POLYMORPHISM - Introduction to Java Programming: Comprehensive Version - page 441

Use the private modifier to hide the members of the class completely so that they cannot
be accessed directly from outside the class. Use no modifiers (the default) in order to allow
the members of the class to be accessed directly from any class within the same package but
not from other packages. Use the protected modifier to enable the members of the class to
be accessed by the subclasses in any package or classes in the same package. Use the public
modifier to enable the members of the class to be accessed by any class.

T ABLE 11.2

Data and Methods Visi bility

Modifier
on members
in a class

Accessed
from the
same class

Accessed
from the
same package

Accessed from
a subclass in a
different package

Accessed
from a different
package

public

✓ ✓ ✓ ✓

protected

-

✓ ✓ ✓

- -

default (no modifier)

✓ ✓

- - -

private

✓

package p1 ;

public class C1 {
public int x;
protected int y;
int z;
private int u;

public class C2 {
C1 o = new C1();
can access o.x;
can access o.y;
can access o.z;
cannot access o.u;

protected void m() {
} can invoke o.m();

} }

package p2;

public class C3
extends C1 {
can access x;
can access y;
can access z;
cannot access u;

public class C4
extends C1 {
can access x;
can access y;
cannot access z;
cannot access u;

public class C5 {
C1 o = new C1();
can access o.x;
cannot access o.y;
cannot access o.z;
cannot access o.u;

can invoke m(); can invoke m(); cannot invoke o.m();

} } }

F IGURE 11.5

Visibility modifiers are used to control how data and methods are accessed.

Your class can be used in two ways: (1) for creating instances of the class and (2) for defin-
ing subclasses by extending the class. Make the members private if they are not intended
for use from outside the class. Make the members public if they are intended for the users of
the class. Make the fields or methods protected if they are intended for the extenders of the
class but not for the users of the class.
The private and protected modifiers can be used only for members of the class.
The public modifier and the default modifier (i.e., no modifier) can be used on members of
the class as well as on the class. A class with no modifier (i.e., not a public class) is not acces-
sible by classes from other packages.