CSC172 Intro

Pepper

Goals

• Reminder of what a class is• How to create and use classes• How to design classes• How to think in terms of objects• How to comment – javadoc

What is a Object Oriented Programming? OOP

• Focus on nouns, things– Rather than verbs, action

• Class is a blueprint for creating an object– Filled with instance variables

• Record State

– Non-Static Methods • Instructions for behavior• Take in parameters and "this" instance (implicit parm)• Special method – Constructor• toString

Picture from: http://javabymanish.blogspot.com/

A Blue Print and an Object

Bike code

• See code: – http://docs.oracle.com/javase/tutorial/java/conce

pts/class.html

• Encapsulation– Mutators & Accessors– Invariants • Exception enforcement

Picture from: http://www.nnwj.de/encapsulation.html

You Try• Create a Card class with toString and

getCardScore method. (Getscore just returns the rank, so A= 1; J=11; Q = 12; K=13 )

• Use 171 Java Tools

Card Class Answer• Link for Card class code

– Notice• Constructor does not create new values• Constructor has no return type and same name• Notice a bad card value will just be created• See use of this• Properties become instance variables• Behaviors become methods• No static

– Documentation! – You now have to do this.• See javadoc toggle view• Class comments• Method comments• Each parameter in and out comments

Scanner reminder

• Bring a Scanner blueprint into your program with an import statement:

import java.util.Scanner;

Our Scanner Guy

• We need to create a Scanner guy (object instance) using the Scanner blueprint (class) and hold him in a Scanner box (variable) Scanner keyb = new Scanner(System.in);

KEYB

Your program talks to user

• System.out.println talks to user, but cannot get responseSystem.out.println(“enter something”);

Reading from the keyboard

• Once we create a Scanner guy (object instance), we can ask our Scanner variable (we called it keyb) to read an integer from the terminal window:variable = keyb.nextInt();

Ask before you read• Scanner takes in typing, but does not ask for

it. You do that:System.out.println ("What is the first value\t?");int value1 = keyb.nextInt();System.out.println ("What is the second value\t?");int value2 = keyb.nextInt();

Now, your variables are inside your program just as if you had set them to a specific number

value 2value1

Other things scanner can read

• You can read:– nextInt()– nextLong()– nextByte()– nextDouble()– next() – up to next whitespace (delimiter) – nextLine() – up to “\n” (end of line)– useDelimiter()

• Reading pointer – nextLine() moves your reading pointer down a line

You Try

• Write a main method– creates 2 cards – prints the cards – prints the sum of the score of the cards. – (Extra – arrays)• fill an array of 5 cards instead using a loop

Game Answer

• Link to Code• Notice: – Created using new and calling constructor– Call methods from the object, not the class– No "this" access

Class Invariants - Exceptions• IllegalArgumentException• How to throw inside class method– throw new IllegalArgumentException("detailed message")

• How to catch inside client method– try/catch block

• try { do the action } • catch (illegalArgumentException ex) { what to do if the try failed;

can use ex variable}

– Or ignore it• throws IllegalArgumentException ( in method header)

Card Exception

• Add exception when Card is sent a bad rank or suit.

• Handle it in the Game

Card Exception Answer• Link for card; Link for game• Notice– Rank test uses an Or , not 1 <= rank <= 13– Suit test uses .equals("CLUBS"), not suit = "CLUBS"– Test input, not instance variable– IllegalArgumentException is an existing exception class in

java.lang• No import

– See why private instance variables are needed?– If there were a setter for these variables, move the code into

a setter and call it

Export and Run on Windows

• Export in BlueJ– Project / Create Jar file– Choose main method

• Run in windows command menu– Start Command– Cd to jar– java –jar < name of jar >

Packages

• Basically a folder that contains folders and classes– package is a namespace that organizes a set of related

classes and interfaces • http://docs.oracle.com/javase/tutorial/java/concepts/

package.html

• Edit / new package• Move classes into the package – Put "package <package name> ; " statement: – Ex: package Pepper;

Packages and Import Statements

• A package is Java’s way of forming a library of classes.

• If you wish to use a package of classes that are not the directory in which you are working, write:import java.util.Scanner; // to include Scanner

Import java.util.*; // to include all of

// java.util’s classes.

Package Names and Directories

• A package can be created by grouping all the classes together in one directory and placing the linePackage PackageName;At the beginning before any Java code.

• Now these classes can be used by adding an import statement to the classes that use it.

Summary

• Design Classes• Create Classes• Create Objects from those classes• Use Scanner• Exceptions• Javadoc – class header, method header with

parms