UML Class Diagram class Rectangle Java Programming Program

UML Class Diagram: class Rectangle Java Programming: Program Design Including Data Structures 1

UML Class Diagram: class Box Java Programming: Program Design Including Data Structures 2

Objects my. Rectangle and my. Box Rectangle my. Rectangle = new Rectangle(5, 3); Box my. Box = new Box(6, 5, 4); Java Programming: Program Design Including Data Structures 3

Abstract Classes s A class that is declared with the reserved word abstract in its heading s An abstract class can contain instance variables, constructors, finalizers, and non-abstract methods s An abstract class can contain abstract methods Java Programming: Program Design Including Data Structures 4

Abstract Classes (continued) s If a class contains an abstract method, the class must be declared abstract s You cannot instantiate an object of an abstract class type; can only declare a reference variable of an abstract class type s You can instantiate an object of a subclass of an abstract class, but only if the subclass gives the definitions of all the abstract methods of the superclass Java Programming: Program Design Including Data Structures 5

Abstract Class Example public abstract class Abstract. Class. Example { protected int x; public void abstract print(); public void set. X(int a) { x = a; } public Abstract. Class. Example() { x = 0; } } Java Programming: Program Design Including Data Structures 6

Interfaces s A class that contains only abstract methods and/or named constants s How Java implements multiple inheritance s To be able to handle a variety of events, Java allows a class to implement more than one interface Java Programming: Program Design Including Data Structures 7

Composition s Another way to relate two classes s One or more members of a class are objects of another class type s “has-a” relation between classes s For example, “every person has a date of birth” Java Programming: Program Design Including Data Structures 8

Composition Example Java Programming: Program Design Including Data Structures 9

Composition Example (continued) Java Programming: Program Design Including Data Structures 10