CSE115 / CSE503 Introduction to Computer Science I. Dr. Carl Alphonce 343 Davis Hall Office hours:

Transcription

1 CSE115 / CSE503 Introduction to Computer Science I Dr. Carl Alphonce 343 Davis Hall alphonce@buffalo.edu Office hours: Thursday 12:00 PM 2:00 PM Friday 8:30 AM 10:30 AM OR request appointment via

2 Dr. Carl Alphonce Turn off and put away electronics: PROFESSIONALISM cell phones pagers laptops tablets etc.

3 Dr. Carl Alphonce Last time Loop/conditional exercises (posted to website) ROADMAP Today Inheritance (introduction) Coming up Inheritance (more)

4 Dr. Carl Alphonce Exam #2 Tuesday 4/12, 9:15 PM - 10:15 PM EXAM INFORMATION Will cover material up to 4/1 (as well as lab 8) If you have a legitimate conflict (work/school): get documentation, scan it as a PDF it to me with subject line: [CSE115] Exam 2 conflict documentation NO LATER THAN 5:00 PM on 4/8 (FRIDAY) A set of sample questions will be posted soon. WEDNESDAY 4/13 IS EXAM MAKE-UP DAY: NO REGULAR LECTURE

5 channel 1

6 What is correct header for a method that iterates through an ArrayList<String> and returns the longest String? A. public String foo(arraylist list, String s) B. public int foo(string<arraylist> list) C. public ArrayList<String> foo(string s) D. public String foo(arraylist<string> list)

7 What is correct header for a method that iterates through an ArrayList<String> and returns the longest String? A. public String foo(arraylist list, String s) B. public int foo(string<arraylist> list) C. public ArrayList<String> foo(string s) D. public String foo(arraylist<string> list)

8 What is correct header for a method that iterates through an ArrayList<String> and returns the longest String? A. public String foo(arraylist list, String s) B. public int foo(string<arraylist> list) C. public ArrayList<String> foo(string s) D. public String foo(arraylist<string> list)

9 Inheritance

10 Example

11 What s wrong with this code? package noninheritance; package noninheritance; public class Cat implements Noisy { public class Dog implements Noisy { private String _myname; private String _myname; public Cat(String n) { _myname = n; public Dog(String n) { _myname = n; public String getname() { return _myname; public String getname() { return public String sound() { return public String sound() { return ruff";

12 Code duplication a code smell package noninheritance; package noninheritance; public class Cat implements Noisy { public class Dog implements Noisy { private String _myname; private String _myname; public Cat(String n) { _myname = n; public Dog(String n) { _myname = n; public String getname() { return _myname; public String getname() { return public String sound() { return public String sound() { return ruff";

13 Number one in the stink parade is duplicated code. If you see the same code structure in more than one place, you can be sure that your program will be better if you find a way to unify them. Refactoring: Improving the Design of Existing Code, Martin Fowler, page 76

14 Inheritance is the fourth relationship we will study this semester. Inheritance It is a relationship between: two classes, OR two interfaces. Inheritance is (syntactically) simple Inheritance is (conceptually) messy

15 original design

16 class to class inheritance I

17 public abstract class Noisy { In code public class Cat extends Noisy { public class Dog extends Noisy {

18 Abstract class A class which mixes method specifications (abstract methods) with fully defined methods (concrete methods) is abstract. An interface contains only abstract methods (they are labelled abstract implicitly).

19 An abstract class must have the abstract keyword in class header. Abstract class Like an interface, an abstract cannot be instantiated.

20 Inheritance ( extends ) Source class: subclass child class derived class Target class: superclass parent class base class

21 Implications of extends Same type implications as for interfaces: instance of subclass belongs to subclass type and superclass type inheritance: non-private members of superclass can be accessed via subclass object. e.g. it s as if methods of superclass were defined in subclass

22 [A] common duplication problem is when you have the same expression in two sibling subclasses. You can eliminate this duplication by using Extract Method (110) in both classes then Pull Up Method (322). Refactoring: Improving the Design of Existing Code, Martin Fowler, page 76

23 class to class inheritance II

24 Code duplication a code smell package noninheritance; package noninheritance; public class Cat implements Noisy { public class Dog implements Noisy { private String _myname; private String _myname; public Cat(String n) { _myname = n; public Dog(String n) { _myname = n; public String getname() { return _myname; public String getname() { return public String sound() { return public String sound() { return ruff";

25 Refactored code (-: a breath of fresh air :-) public abstract class Noisy { private String _myname; public Noisy(String name) { _myname = name; public abstract String sound(); public String getname() { return _myname; public class Cat extends Noisy{ public Cat(String n) { public String sound() { return "meow"; public class Dog extends Noisy{ public Dog(String n) { public String sound() { return ruff";