1. CSE115: Introduction to Computer Science I Dr. Carl Alphonce 343 Davis Hall 645-4739 alphonce@buffalo.edu 1

2. Agenda Announcements – Cell phones / laptops off & away / Name signs out Last time –Composition relationship –Lifetime/Scope Today –Unified Modeling Language (UML) composition –Naming conventions –Methods

3. whole/part creation in code (elaborated) Whole creates instance of part in its constructor In Java code, involves 3 changes to whole class: –Declaration of instance variable of part type –Instantiation of part class in whole class constructor –Assignment of new part instance to instance variable

4. 4 Dog – Tail example in Java package cse115; public class Dog { private Tail _tail; public Dog() { _tail = new Tail(); }

5. UML Unified Modeling Language (Class Diagrams)

6. UML Unified Modeling Language –express design without reference to an implementation language For example

7. Composition in UML

8. Binary Class Relationships: directional binary  two classes are involved – source class has code modification – target class does not composition –source: WHOLE –target: PART in diagram: –line decoration is on source/WHOLE –show only detail that’s needed/desired

9. package cse115; public class Dog { public Dog() { } package cse115; public class Tail { public Tail() { }

10. package cse115; public class Dog { private Tail _tail; public Dog() { _tail = new Tail(); } package cse115; public class Tail { public Tail() { }

11. Naming conventions packages: all lower case classes: –first character: upper case letter –camel case afterwards instance variables –first character: underscore ‘_’ –camel case afterwards local variables –first character: lower case –camel case afterwards

12. package lab2; public class EcoSystem { private example1.Terrarium _t; public EcoSystem() { _t = new example1.Terrarium(); } public void addTwoCaterpillars() { example1.Caterpillar c1 = new example1.Caterpillar(); example1.Caterpillar c2 = new example1.Caterpillar(); _t.add(c1); _t.add(c2); c1.start(); c2.start(); } Constructor definition Method definition

13. package lab2; public class EcoSystem { private example1.Terrarium _t; public EcoSystem() { _t = new example1.Terrarium(); } public void addTwoCaterpillars() { example1.Caterpillar c1 = new example1.Caterpillar(); example1.Caterpillar c2 = new example1.Caterpillar(); _t.add(c1); _t.add(c2); c1.start(); c2.start(); } The scope of an instance variable declaration is the entire class body. The variable can (and should) be assigned an initial value (initialized) in… The variable can be used in any method of the class. Here’s a method definition. Both the constructor and this method are in the scope of the instance variable declaration. The instance variable can (and should) be assigned an initial value (initialized) in… the constructor. It can be used in any method in class body.

14. Method definition syntax public void addTwoCaterpillars() { example1.Caterpillar c1 = new example1.Caterpillar(); example1.Caterpillar c2 = new example1.Caterpillar(); _t.add(c1); _t.add(c2); c1.start(); c2.start(); } method definition

15. Method definition syntax public void addTwoCaterpillars() { example1.Caterpillar c1 = new example1.Caterpillar(); example1.Caterpillar c2 = new example1.Caterpillar(); _t.add(c1); _t.add(c2); c1.start(); c2.start(); } Remember that method definition consists of both a method header a method body.

16. Method definition syntax public void addTwoCaterpillars() { example1.Caterpillar c1 = new example1.Caterpillar(); example1.Caterpillar c2 = new example1.Caterpillar(); _t.add(c1); _t.add(c2); c1.start(); c2.start(); } Here’s the method body.

17. Method definition syntax public void addTwoCaterpillars() { example1.Caterpillar c1 = new example1.Caterpillar(); example1.Caterpillar c2 = new example1.Caterpillar(); _t.add(c1); _t.add(c2); c1.start(); c2.start(); } The method header begins with an access control modifier, public in this case.

18. Method definition syntax public void addTwoCaterpillars() { example1.Caterpillar c1 = new example1.Caterpillar(); example1.Caterpillar c2 = new example1.Caterpillar(); _t.add(c1); _t.add(c2); c1.start(); c2.start(); } return type specification ‘void’ is a special return type specification, indicating that no value is returned by the method

19. Method definition syntax public void addTwoCaterpillars() { example1.Caterpillar c1 = new example1.Caterpillar(); example1.Caterpillar c2 = new example1.Caterpillar(); _t.add(c1); _t.add(c2); c1.start(); c2.start(); } Next comes the name of the method. Method names follow the same convention as local variables

20. Method definition syntax public void addTwoCaterpillars() { example1.Caterpillar c1 = new example1.Caterpillar(); example1.Caterpillar c2 = new example1.Caterpillar(); _t.add(c1); _t.add(c2); c1.start(); c2.start(); } parameter list – empty in this example remember:argument list  method call parameter list  method definition

21. Method definition syntax public void addTwoCaterpillars() { example1.Caterpillar c1 = new example1.Caterpillar(); example1.Caterpillar c2 = new example1.Caterpillar(); _t.add(c1); _t.add(c2); c1.start(); c2.start(); } method body – delimited by braces

22. Method definition syntax public void addTwoCaterpillars() { example1.Caterpillar c1 = new example1.Caterpillar(); example1.Caterpillar c2 = new example1.Caterpillar(); _t.add(c1); _t.add(c2); c1.start(); c2.start(); } statements & (local variable) declarations – consists of local variable declarations and statements, which in this case are all method calls.