INHERITANCE AND POLYMORPHISM - Java Programming: From Problem Analysis to Program Design - page 661

between package access and protected accesses of a member. If a member of a class has a
package access, that member can be directly accessed in any class contained in that package,
but not in any class that is not contained in that package even if a subclass is derived from
the class containing that member and the subclass is not contained in that package. On the
other hand if a member of a class is protected , that member can be directly accessed in any
subclass even if the subclass is contained in a different package.
Consider the following class definition:
public class Rectangle
{

double length;
double width;

public Rectangle()
{

length = 0;
width = 0;

}

double area()
{

return length * width;

}
.
.
.

}
In this class definition, the data members length and width and the method area have
package access.

1
0

class Object
In Chapter 8, we defined the class Clock and later included the method toString to
return the time as a string. When we included the method toString , we noted that every
Java class (built-in or user-defined) is automatically provided the method toString .Ifa
user-defined class does not provide its own definition of the method toString ,thenthe
default definition of the method toString is invoked. The methods print and println
use the method toString to determine what to print. As shown in Chapter 8, the default
definition of the method toString returns the class name followed by the hash code of the
object. You might ask, where is the method toString defined?
The method toString comes from the Java class Object , and it is a public member
of this class. In Java, if you define a class and do not use the reserved word extends to
derive it from an existing class, then the class you define is automatically considered to be
derived from the class Object . Therefore, the class Object directly or indirectly
becomes the superclass of every class in Java. From this, it follows that the definition of
the class Clock (previously given in Chapter 8):