Inheritance Systems. Merchandise. Television Camcorder Shirt Shoe Dress 9.1.1

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1 Merchandise Inheritance Systems Electronics Clothing Television Camcorder Shirt Shoe Dress Digital Analog 9.1.1

2 Another AcademicDisciplines Hierarchy Mathematics Engineering Algebra Probability Geometry Industrial Civil Electrical 9.1.2

3 Ancestors ClosedFigure & Descendants Ellipse Polygon Circle Triangle Quadrilateral Pentagon Square 2006 Pearsn Addison-Wesley. All rights reserved 9.1.3

4 ClosedFigure Conformance A type conforms to itself and any ancestor. Ellipse Circle Triangle Polygon Quadrilateral A conforms to B means A B Pentagon Square Conformance is! 9.1.4

5 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); public void method(parm1, parm2, parmn) { expressions expression arg1 must conform to parm1 arg2 must conform to parm2... argn must conform to parmn Anything with type that conforms to expression can be substituted in its place. Remember: Conformance is directional! 9.1.5

6 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() JComponent Inheritance 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 ) Line Rectangle Oval 9.1.6

7 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? 9.1.7

8 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)

9 Object Every class inherits from a class called Object. The println method is overloaded. One version of println is defined as follows. public void ( Object x ) { println( x.tostring() ); Object... «query» + boolean equals( Object ) + String tostring()... Oval could override tostring() in the following manner. public String tostring() { String result = "Oval object" + "\n"; result = result + " x: " + getx() +", y: "+gety(); result = result + " width: " + getwidth() +", height: "+getheight() + "\n"; if (getparent() == null) { result = result + " not added, \n"; else { result = result + " is added, \n"; result = result + " color: "+colorstring(getbackground()); return result; 9.2.9

10 Equality There are two different kinds of equality for reference data. equality means that two expressions have the same identity. (i.e., the two expressions represent the same object.) equality means that two expressions represent objects with the same value/content. The == symbol tests for identity equality, when applied to reference data. Example Oval ov1, ov2; ov1 = new Oval(0, 0, 100, 100); ov2 = new Oval(0, 0, 100, 100); if (ov1 == ov2) { System.out.println( identity equality ); else { System.out.println( not identity equality );

11 Content Equality The equals method from Object provides a potential content equality check. Example public class MyOval extends Oval {... public boolean equals(object z) { return (z instanceof Oval) && ((Oval)z).getX() == getx() && ((Oval)z).getY() == gety() && ((Oval)z).getWidth() == getwidth() && ((Oval)z).getHeight() == getheight() && ((Oval)z).getBackground() == getbackground() && ((Oval)z).getParent() == getparent();