1. Class Hierarchies and Type Conformance
Lecture 9.1
Class Hierarchies and Type Conformance

2. Inheritance Systems Merchandise Electronics Clothing Television
Camcorder
Shirt
Dress
Shoe
Digital
Analog
© 2006 Pearson Addison-Wesley. All rights reserved

3. Another Hierarchy AcademicDisciplines Mathematics Engineering Algebra
Geometry
Industrial
Electrical
Civil
Probability
© 2006 Pearson Addison-Wesley. All rights reserved

4. Ancestors & Descendants ClosedFigure Ellipse Polygon Circle Square
Quadrilateral
Pentagon
Triangle
Ancestors
Descendants
© 2006 Pearson Addison-Wesley. All rights reserved

5. Conformance ClosedFigure Ellipse Polygon Circle Square Quadrilateral
Pentagon
Triangle
A type conforms to
itself or any ancestor.
A conforms to B
means
A is_a B
Conformance
is directional!
© 2006 Pearson Addison-Wesley. All rights reserved

6. Rule for Using Conformance
An expression is permitted anywhere that its type conforms.
assignment
object = expression;
expression must conform to object
parameter passage
object. method(arg1, arg2, … argN);
arg1 must conform to parm1
arg2 must conform to parm2
...
argN must conform to parmN
public void method(parm1, parm2,…parmN) { … }
expressions
expression
Anything with type that
conforms to expression can be
substituted in its place.
Remember: Conformance is directional!
© 2006 Pearson Addison-Wesley. All rights reserved

7. javax.swing.JComponent
java.awt.Component
«queries»
+ Color getBackground()
+ Color getForeground()
+ int getX()
+ int getY()
+ int getWidth()
+ int getHeight()
+ Container getParent()
«update»
+ void setBackground( Color )
+ void setForeground( Color )
+ void setBounds(int, int, int, int)
+ void setSize( int, int )
+ void setLocation( int, int )
+ void paint( Graphics )
+ void repaint()
java.awt.Container
«update»
+ void add( Component )
+ void add( Component, int )
+ void remove( Component )
+ void removeAll( )
javax.swing.JComponent
«constructor»
+ JComponent()
«queries»
+ int getX()
+ int getY()
+ int getWidth()
+ int getHeight()
«update»
+ void paint( Graphics )
+ void paintChildren()
+ void setBackground( Color )
+ void setForeground( Color )
Component -- note getParent returns the object to which the Component has been added or null.
The add method with no second container adds UNDERNEATH existing children. removeAll removes all children.
JComponent
Inheritance
© 2006 Pearson Addison-Wesley. All rights reserved
Oval
Rectangle
Line

8. Using Inheritance and Conformance
Write a function that returns true exactly when its Oval parameter
has a height of 10 or greater.
public boolean isTenOrMoreHigh( Component v ) {
return v.getHeight() >= 10; }
What is the advantage of using a parameter of type Component, instead of an Oval?
© 2006 Pearson Addison-Wesley. All rights reserved

9. Testing for Type conformance
Java provides the following operator to test for type conformance.
instanceof
Syntax
expression instanceof className
Semantics
This is a Boolean expression that evaluates to true exactly
when the type of expression conforms to className.
Example
if (myVar instanceof Component) ...
© 2006 Pearson Addison-Wesley. All rights reserved