1. DEFINING CLASSES FOR
INHERITANCE
Chapter 8.1:

2. INHERITANCE: What is
Inheritance?
 Inheritance let us to create a new class from the
existing classes.
 The new class is called subclass and the existing
class is called superclass.
 The subclass inherits the properties of the
superclass.
 The properties refer to the method or the attribute
(data)
 Inheritance is ‘is-a’ relation
 Example : if a Circle inherits the Shape class,
hence the Circle is a Shape. (see the next figure)

3. INHERITANCE: Example
The class Circle and Rectangle are derived from Shape and the class Box
is derived from Rectangle.
Every Circle and every Rectangle is Shape and every Box is a Rectangle

4. INHERITANCE: When it is used?
 If we need a new class with a same properties or
method of the current class, we do not need to
define a new class.
 A new class might be inherited from the current
class.

5. INHERITANCE: Types of
Inheritances?
 Single inheritance
 Is a subclass that derived from a single/one superclass
(existing class)
 Multiple inheritance
 Is a subclass that derived from more than one superclass
 Not supported by Java

6. Geometry
Circle Triangle Square
Sphere Cone Cylinder Cubes
Single Inheritance
Multiple Inheritance

7. INHERITANCE:
Properties/Characteristics?
 Involve 2 classes :
 Super class.
 Sub class
Rectangle
Box
Super class
Sub class

8. INHERITANCE: Super class and
Sub class
Rectangle
double length
double width
Box
double height
 Super class – Rectangle
 Sub class – Box
 Attributes for Rectangle : length, width
 Attribute for Box : height
Box class inherits the length and width of the
Rectangle class (superclass)

9. INHERITANCE: keyword extends
 extends is the keyword to implement inheritance
in Java.
 Syntax
class SubClassName extends SuperClassName
{
// properties & methods
}
 E.g.
class Box extends Rectangle
{
// properties and coding
}
Rectangle
Box

10. E.g. : Rectangle class
public class Rectangle
{
private double length;
private double width;
public Rectangle()
{
length = 0;
width = 0;
}
public Rectangle(double L, double W)
{
setDimension(L,W);
}
public void setDimension(double L, double W)
{
if (L >= 0)
length = L;
else
length = 0;
if (W >= 0)
width = W;
else
width = 0;
}
public double getLength()
{
return length;
}
public double getWidth()
{
return width;
}
public double area()
{
return length * width;
}
public void print()
{
System.out.print(“length = “ + length);
System.out.print(“width = “ + width);
}
} // end for Rectangle class

11. Rectangle
- length : double
- width : double
+ Rectangle()
+ Rectangle(double,double)
+ setDimension(double,double) : void
+ getLength() : double
+ getWidth() : double
+ area() : double
+ print() : void
The class Rectangle has 9 members
UML class diagram of the Rectangle class

12. E.g. : Box class
public class Box extends Rectangle
{
private double height;
public Box()
{
super();
height = 0;
}
public Box(double L, double W, double H)
{
super(L,W);
height = H;
}
public void setDimension(double L, double W, double H)
{
setDimension(L,W);
if (H >= 0)
height = H;
else
height = 0;
}
public double getHeight()
{
return height;
}
public double area()
{
return 2 * (getLength() * getWidth()
+ getLength() * height
+ getWidth() * height);
}
public double volume()
{
return super.area() * height;
}
public void print()
{
super.print();
system.out.print(“height = “ + height);
}
} // end for class Box extends

13. UML class diagram of the class Box
Box
- height : double
- length : double (can’t access directly)
- width : double (cant’ access directly)
+ Box()
+ Box(double,double)
+ setDimension(double,double) : void
+ setDimension(double,double,double) : void
(overloads parent’s setDimension())
+ getLength() : double
+ getWidth() : double
+ getHeight() : double
+ area() : double (overrides parent’s area())
+ volume() : double
+ print() : void (overrides parent’s print())
The class Box has 13 members

14.  Declaring Arrays and Accessing Array Components
 The class Box is derived from the class Rectangle
 Therefore, all public members of Rectangle are public members of
Box
 The class Box overrides the method print and area
 The class Box has 3 data members : length, width and height
 The instance variable length and width are private members of
the class Rectangle
 So, it cannot be directly accessed in class Box
 Use the super keyword to call a method of the superclass.
 To print the length and width, a reserve word super should be put
into the print method of class Box to call the parent’s print()
method.
 The same case happen in the volume method where super.area()
is being used to determine the base area of box.
 The method area of the class Box determines the surface area of
the box.
 To retrieve the length and width, the methods getLength and
getWidth in class Rectangle is being used.
 Here, the reserve word super is not used because the class Box
does not override the methods getLength and getWidth