9/19/2018 Programming Data Structures. Polymorphism And Abstract

Transcription

1 9/19/2018 Programming Data Structures Polymorphism And Abstract 1

2 In-class assignment: deadline noon!! 2

3 Overview: 4 main concepts in Object-Oriented Encapsulation in Java is a mechanism of wrapping the data (variables) and code acting on the data (methods) together as a single unit. Inheritance in java a mechanism wherein a new class is derived from an existing class. Polymorphism Abstraction [1] [2] 3

4 Chapter 8.1 Polymorphism 4

5 Example: Ant and Doodlebug Critter Prey Predator 5

6 Example: Ant and Doodlebug Critter move move move Prey Predator 6

7 Assignment setup 1. Create a project named assignment04 2. Create a public class, called Critter 3. Create two public classes, Ant, and, Doodlebug 7

8 Assignment setup (cont.) 1. Make Ant and Doodlebug as derived classes from Critter 2. All the three classes, Critter, Ant, Doodlebug have a method: move, return type is void, and does not have any input parameter 1. move in Critter should be empty. 2. move in Ant should print ant move 3. move in Doodlebug print doodlebug move 8

9 Assignment setup (cont.) 1. Create a public Main class 2. Create a public static entry method, which is: 3. Inside this main method: Create a Critter variable critter1 and critter2 Initialize critter1 with Initialize critter2 with 9

10 Assignment setup (cont.) 1. Inside the main method: Call critter1.move() and critter2.move() 2. Run the main method 10

11 Introduction to Polymorphism (1 of 2) Polymorphism is the ability to associate many meanings to one method name

12 Introduction to Polymorphism (2 of 2) Polymorphism allows changes to be made to method definitions in the derived classes, and have those changes apply to the software written for the base class

13 Abstract classes Now we have three move methods definitions. Actually, we only need two move definitions, because for a Critter to move, we need to know which type of Critter it is (whether it s ant or doodlebug) Let s try to remove move inside class Critter 13

14 Assignment setup Abstract class intro Fix the error in the previous slide without adding the definition of move in Critter class is used to postpone the definition of a method If a class has an abstract method, the class has to be marked as, too 14

15 Assignment setup (cont.) Introducing dimensional array

16 Assignment setup - 1. Create a public class World 2. Add a private variable,, which is a 2- dimensional array in which each cell/element is a (can be either an ant or a doodlebug) 3. Add a constructor of World, the input is, and inside the constructor, you need to initialize the variable. Recall in assignment02, how did you iterate the 2-dimensional array? here, you need to iterate grid, and initialize each cell with null 16

17 Assignment setup (Cont.) Create a public method in World,, inside the Display method, print the : 1. Iterate through the 2. For each row, print a, which is a new line character 3. For each cell, 1. print., if the cell is null 2. Print x, if the cell is an ant 3. Print o, if the cell is a doodlebug 17

18 In-class Assignment (Cont.) Go to Main class, and commented out the four lines in main method. In the main method: 1. Create a new variable ; 2. Call the method, 3. You should see 20 lines of dots (why?) 18

19 Grading rules (2 points in total) You need to have the same class diagram as we do in the previous slides. Each violation will cost you 0.1 You need to have the same method declaration as we do in the previous slides. Each violation will cost you 0.1 Each wrong method definition will cost you 0.2 If the end result is incorrect, at most, you can get

20 Take-home Assignment (cont.) How to assign an ant or a doodlebug in the grid? 1. Create a public method in World class: 2. The input is the number of ants to be created and added to the grid, the input is the number of doodlebugnumber to be created and added to the grid. 20

21 Take-home Assignment (cont.) 1. Inside the method : create instances stored in cells (the locations of ants are random) create stored in are random) instances cells (the locations of doodlebugs 21

22 Grading rules (in total 2.5 points) If you have a method declared correctly, you get 0.5. If method creates the correct number of ants, and assigns the ants to grid cells randomly, you get 1 point. If method creates the correct number of doodlebugs, and assigns the doodlebugs to grid cells randomly, you get 1 point. 22

23 Quiz on next Wednesday, 9/26 Questions are from: All the slides from 9/5 to 9/24 All the assignments from 9/5 to 9/24 Topics include 2-dimensional arrays, encapsulation, inheritance, packages, polymorphism, abstract classes. Open-book 30 min 23