1. עקרונות תכנות מונחה עצמים תרגול 10: Generics

2. Outline  Generic classes  Generics & Inheritance  Wild Cards  Case study: Generic Graph

3. Generic Classes – Motivation List v = new ArrayList(); v.add("test"); Integer i = (Integer)v.get(0); // runtime error List v = new ArrayList (); v.add("test"); Integer i = (Integer)v.get(0); // compilation error

4. Generic Classes  A class is generic if it declares one or more type variables.  These type variables are known as the type parameters of the class.  The type variables can be used as:  Method parameters.  Return value.  Local variables.

5. Generic Classes – Example public interface List { void add(E x); Iterator iterator(); } public interface Iterator { E next(); boolean hasNext(); } public class ArrayList implements List { private E[] _data;... }

6. Generic Classes vs Concrete Classes  Generic Class declaration defines a set of parameterized types, one for each possible invocation of the type parameter section.  All compiles to the same.class file.  All uses the same.class file at runtime.

7. Generic Classes VS Concrete Classes (Example) public class ArrayList implements List { private E[] _data;... } List v; v = new ArrayList (); Generic class Compile to ArrayList.class Concrete class Uses ArrayList.class

8. Generics & Inheritance

9. Assignments roles:

10. Using wild cards – Motivation Vector animals; Vector cats = new Vector (); animals = cats; animals.add(new Dog()); Cat cat = cats.elementAt(0); // compilation error!!! Animal animal; animal = new Dog(); Cat cat = animal; // compilation error!!!

11. Using wild cards

13. Using wild cards – example: public static void makeNoise (Vector animals) { for (Animal animal:animals) { animal.say(); } { Vector cats = new Vector (); makeNoise(cats); public static void makeNoise (Vector animals) // compilation error!!!

14. Using wild cards – example: Vector animals = null; Vector cats = new Vector (); animals = cats; animals.add(new Dog()); Cat cat = cats.elementAt(0); // compilation error!!! animals.add(null); - The only one that allows.

15. Using wild cards – examples: Vector animals = new Vector (); Vector cats = new Vector (); Vector animals2 = new Vector (); Vector cats2 = new Vector (); animals.add(new Cat()); cats.add(new Cat()); animals.add(null); Cat cat = animals.elementAt(0); Animal animal = cats.elementAt(0); Cat cat2 = animals2.elementAt(0); Animal animal2 = animals2.elementAt(0); Object o = animals2.elementAt(0); // compilation error

16. Question from 2013 test. נתון שהמחלקה B יורשת מהמחלקה A, והמחלקה G היא גנרית עם פרמטר יחיד. מה צריך להיות הפרמטר X כדי שההשמה הבאה תהיה תקפה ע " פ כללי הטיפוסים של ג ' אווה ? G g = new G (); א. A ב. extends A ? ג. super A ? ד. super B ? ה. תשובות ב, ד נכונות ו. תשובות א, ג נכונות

17. Case study: Generic Graph

18. Graph

19. Graphs can model  The internet  Maps  Social networks  …

20. Graph Representation

21. The vertex class

22. The Graph Class

23. Vertex class - code

24. Graph class - code

25. DFS Tour

27. Execution example

28. The Weighted interface

29. Weight query

30. Usage example

31. Usage example (cont.)

32. Exception handling

34. Summary