Java Programming. Computer Science 112

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1 Java Programming Computer Science 112

2 Homework thoughts. Zip. The. Src. Folder. A "Get" function shouldn't change anything. That's what Set does. An "IsXxxx" function shouldn't change anything. It's just a question. Get for bool. There is no "const" in Java. You double-must use packages from now on. Anything in the default package won't be graded. if( tcookie.mcooked = true )!?!?!?

3 Zip. The. Src. Folder. EZ-Bake Oven was a copy of last week's homework with the names changed. Make a Cookie/Ball, an Oven/Batter, and a Person/Fielder. Give the cookie to the oven to cook. Give the cookie to the person to eat. Cookie tcookie = null;// No cookie yet Oven toven = new Oven(); Person = new Person(); // Get type from user, then tcookie = new Cookie(type); toven.cook(tcookie); tperson.eatcookie(tcookie);

4 Hard Bake burned up Step one - if I give you the answer, use it Step two through ten - Imma do it on board

5 Object Recap Object is a Thing that you create with 'new' It has private properties and public methods 'static' methods are for when you are talking about the Class itself and not one particular object. You can have many variables "point" at an object, but there is only one object per new.

6 Summer kids do EZ-Bake together Wouldn't it be cool if the first eight lectures here were their own class and then I didn't have to do all of Java in the last eight? Good thing we are 52nd worldwide in education funding This is not a political statement. It's statistics. US Dept of Commerce, Economics, and Statistics. World Bank Human Development Indicators Always get two sources Not wikipedia

7 So about those cookies We made a Cookie class that had a flavor just as a string. But what if peanut butter and oatmeal raisin cookies need different time to cook? You could have if-elses control if it was cooked enough What if they reacted differently to heat? More special cases in Cook maybe What if there needs to be 20 kinds of cookie That's a lot of if-elses... And 5 programmers working on the project This is starting to suck

8 Now introducing Super-Peanuts! Now there is a kind of peanut butter cookie that is exactly like a regular peanut butter cookie except if it gets above 355 degrees it explodes. The Cookie class is 15,000 lines by now, so you better not miss a spot that needs to check if the cookie type is explosive. Wouldn't it be nice if this could be organized better?

9 Inheritance to the rescue "A peanut butter cookie IS A cookie" Is-a is the entire idea here. Let's make a PeanutButterCookie class that IS A Cookie in every way, but can handle PB-specific stuff. public class PeanutButterCookie extends Cookie void Cook() syso( this + " kills anyone who is allergic nearby." ); mcooked = true;

10 PeanutButterCookie is still a Cookie Even though it only appears to have Cook, it inherits all of Cookie. The Cook method is an exact match of Cookie's version, so it "overrides" it. Everything else it lets through to Cookie. Cookie PeanutButterCookie

11 Try it, you'll like it Make a new class called AsbestosCookie in your awesome EZ Bake Make one method - Cook. The signature (declaration) must be the exact same. Make it do nothing because rocks don't cook Asbestos is the bestest Have main create an AsbestosCookie instead Run the program

12 Adding instead of replacing In those examples we Overrode the existing functionality. Replaced it entirely. We can Add to what our superclass does too Make a TemporalCookie that inherits from Cookie. If we Cook it three times it goes back to raw. void Cook() super.cook();// Do regular cookie stuff mcookcalls++;// something to track how many times we've been cooked if (mcookcalls == 3) mcookcalls = 0; SetCooked( false );

13 Inheritance thoughts When planning your classes, make sure you only use inheritance for ISA HASA is different. An Oven HAS A Door. You can't inherit directly from two things. But you can inherit from something that inherits from something. OatmealCookie ISA Cookie ISA Food ISA Object Private is still private. OatmealCookie can't see mcooked in Cookie.

14 Inheritance constructors A subclass's constructor needs to call a superclass constructor. If you don't, you'll get the default one. Cookie doesn't have a default one. Cookie requires a type, but an OatmealCookie knows its own type... It doesn't have to call the same one though. In main: Cookie tone = new OatmealCookie();// Cookie needs an arg, Oatmeal doesn't In OatmealCookie: public OatmealCookie() super("oatmeal Cookie");// Like backwards compatibility

15 Now you have to Think The idea of this lecture is one sentence long. But now you must program goodly. Practice 1: At a Bank, everything you do is a Transaction. Every transaction prints your balance. There are Deposit and Withdrawal types of Transactions. Withdrawals spit out money

16 Bank Plan Bank() MakeDeposit( Deposit ) // These change the mbalance and call MakeWithdrawal( Withdrawal ) // float mbalance & GetSet Transaction(float tamount) float mamount & Get/Set TransactionFinished(Bank) Withdrawal(float tamount) extends Transaction TransactionFinished(Bank) Deposit(float tamount) extends Transaction TransactionFinished after // Prints out the new balance // Spits out money and calls super // No TF, so goes straight to T's level This lecture is going for "Specific types of a thing do something differently, but all types do some things the same."

17 Bank Code class Transaction public void TransactionFinished(Bank tbank) System.out.println("New balance " + tbank.getbalance(); class Withdrawal extends Transaction public void TransactionFinished(Bank tbank) // Something that removes money, then "pass it up" super.transactionfinished(tbank); In this program, main would then make a transaction, and give it to the bank. Withdrawal tw = new Withdrawal(400); tbank.makewithdrawal(tw);

18 Think more Practice 2: Every Employee has to CheckOut of the Office when they leave for the day. This prints their ID to a report. There are Bosses and Grunts at the company. Before a Boss Leaves, he GrabsABeer.

19 Employee Plan Office CheckOut(Employee) Employee Leave() Office mworkplace Boss extends Employee Leave() Grunt extends Employee Leave()

20 Employee Code class Employee Office mworkplace; public void Leave() mworkplace.checkout( this ); class Boss extends Employee public void Leave() super.leave(); GrabABeer(); void GrabABeer() Here, main would call Leave on everybody using your for-loop tattoo for arrays. for( int i = 0; i < memployees.length; i++ ) memployees[i].leave();

21 Are you getting it? Inheritance is for making categories or types or subsets etc of a main object. Any behaviors that every single child type does go in the "Baseclass" Specific stuff goes in the children, and they call "super" to get to the shared code. Let's chill here. Next week is the more difficult kind of inheritance where it kinda goes backwards. And we are in the "whole point" part of the class.

22 Cool down time Don't forget about tostring(). It can help you debug multiple layer obejcts It itself is a great example of using "super" You never call it explicitly Sometimes you need to know what the heck an object actually is. You have a variable of type Employee and want to know if it is a Boss. You have a Transaction and want to know if it is a Withdrawal "instanceof" lets you ask an Object what it is, and "casting" lets you use it that way.

23 instanceof Employee tbob = new Boss(); // Totally legit. Boss ISA Employee if( tbob instanceof Boss ) Boss tbobasboss = (Boss)tBob; Make sure the object really is a boss By referring to it as a Boss we could call Boss-specific methods like GrabABeer Next week we'll see that you don't need to in some cases. Still only one person since only one new.

24 This one's for you I want to print the menu of every restaurant on my street. I have an array trestaurants in my main, and main makes a TacoBell and a CarlsJR. TacoBell ISA Restaurant. So is CarlsJR. Arguable All menus print the address first, then the items depend on the specific restaurant. If you finish that, what if I wanted the ability to know how many TacoBell's existed...

25 For the homework I don't tell you the definitions of the classes any more. Not that you listened... *sniff* When designing classes, keep some things in mind. Data should be private Inheritance means ISA If every type can do something, the code goes in the baseclass. Methods should be exactly as long as they should be. Don't forget you have a textbook!

CONTENTS: What Is Programming? How a Computer Works Programming Languages Java Basics. COMP-202 Unit 1: Introduction

CONTENTS: What Is Programming? How a Computer Works Programming Languages Java Basics COMP-202 Unit 1: Introduction Assignment 1 Assignment 1 posted on WebCt and course website. It is due September 22nd