Java Programming. Computer Science 112

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Gregory Morton
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1 Java Programming Computer Science 112

2 Objects OBJECTS ARE AWESOME

3 They are awesome It's the whole point of programming Things that are good but aren't essential to getting a job Knowing a particular language Having written your own programs on the side A degree What actually matters Experience working in a group Problem solving Object modeling

4 This class just got real Congrats on making it here without dropping If you have less than 50% right now, you should maybe withdraw and try again next semester All we've done so far is learn the alphabet. Now we speak. *waits for people to leave* *sobs softly*

5 This will click Once you Get It, you will see the world differently. You will model the traits and behaviors of everything you see. You will find problems in the physical world that you will want to recompile.

6 A rock All Objects have two things in common Properties, or what they are Methods, or what they can do Properties are just variables A rock has a color A rock has a weight Methods are just functions Rocks don't really do anything public class Rock // This is in its own file - rock.java { } float mweight; Color mcolor;

7 class vs object A class is the concept of a thing. The great Rock spirit. The idea of a rock. A Rock object is actually a Rock. The class definition says all rocks have a color and a weight. But each Rock object has its own value for each. Class is the definition or template for making a Rock. Rock trock = new Rock();

8 A method to the madness There is a class Lamp. It has properties and methods. Properties Number of bulbs Max Wattage Methods Turn Switch Unplug Methods are actions you perform on the object. Lamp tlamp = new Lamp(); tlamp.turnswitch();

9 Mind == Blown Each time you make a new Lamp, it creates a totally separate entity, even though there is still just the one class. Object programming is awesome because it is how the world works Lamp tlamp = new Lamp(); Lamp tlamp2 = new Lamp(); tlamp.turnswitch(); // tlamp2 is NOT on.

10 Methods are Functions in an Object Our static functions last week existed in the aether with main. To call a method, you logically need an object. You can't call TurnSwitch() on the Great Lamp Spirit But you can use static again static int AWickedCoolFunction from last week belonged to the Great MainClass Spirit. Static is rarely the right answer, so just pretty much don't use it. Like how Eclipse tries to add semicolons to if statements, it will try to get you to add static.

11 My brain hurts Deep breath The Class defines the properties and methods of an object The Class may have static methods that apply to the idea of the class You use a class to create an Object of that type. The object actually exists. Each object has its own values for the properties Calling a method on an object doesn't affect any other object.

12 Wakey wakey time Define a TV class on yo card What properties does a TV have? Don't forget that you need to say what type each variable is- "float mheight" This includes permanent (mheight) and temporary (mon) Pick four What can you do with a TV? Does the method need any arguments? Does it return anything to the caller? Pick two, plus one static Static is black hoodoo, but you need to see it to

13 MTV TV int mchannel; String mcolor; float mscreendiagonal; boolean mison; boolean SetChannel( int tchannel ); void ToggleOn(); String GetCurrentShow(); static boolean IsElectricalAppliance();

14 UML is like a flowchart for Classes Always plan everything ahead on paper before you start Or at least Notepad Scribbles on Post-Its are okay too But really, it isn't just to help you write it. It's to make sure you are writing the correct thing It is just properties and methods now as we start with a single class. We'll come back and add arrows. Remember, object modeling is the Whole Point of programming. It's the OO in OOP.

15 VH1 BadTV float mchannel; String mcurrentshowtitle; int mshowminutes; String mleadactor; String mthatoneactressheusedtodate; The TV should not care about anything that is not TV related. There would be a separate class for Show here. And Actor.

16 Unhealthy Choice 1) Chef 2) Oven 3) Customer 4) Waiter 5) Freezer 6) Meatloaf (I finally remembered Summer has five rows. This is just a Rock.) Each of the six rows here represent one of these Objects. We are modeling a restaurant that just serves reheated frozen dinners. Like Chili's. So who needs to start off the process, and what does he need to say or do? We are sitting at the table, and want to end with stomach cramps.

17 Blah blah blah, how do I make one? No blah blah blah! Captain Kirk? Anyone? Each class gets its own file Until next week, where we learn access levels, but just go with it. Just make a new class like you have been and make sure the checkbox for "create main" is off. They just end up next to each other. Only ONE has a "main" though.

18 Pause on this A file can have just one public class. TV.java <-- And the name matches the class name. package MainPackage; public class TV { boolean mison; String mbrandname; void ToggleOn() { mison =!mison; } static boolean IsElectricalAppliance() { return true; } }

19 What's with all the public? It's the same thing as "What's with all the static" from last week. Mark everything public for now and we'll do other things later. Short answer "Let people outside this file see me".

20 You know how to do this part You have made Scanners and Randoms before. Creating your custom object is the same thing. SomeClass tanobject = new SomeClass(); tanobject.amethod();...that was easy.

21 One Object per new This is another good tattoo. Whenever you pass an object to another function, you are actually passing that object OOP is so awesome again for making the perfect analogy I have a piece of paper, I hand it to you, you write on it. When I get it back, it is written on. "void WriteHiOnPaper( Paper tpiece )" Note, you do not "return" it. I made an object, you fiddled it, it was changed.

22 Programming sing-along Make your TV class. Make a main that instantiates (makes) an object Have each of the methods just do a System. out that says what they did. "You called Channel Up!" Make a menu with a choice for each method. If you still don't have a handle on the menu loop, look back at Homework 7.

23 Schizophrenic!= MPD What if an object needs to talk to itself? The method "Channel Up" wants to first check what the "Max Channel" is. Any method can use any property or method of itself just like normal. But sometimes Graham needs to refer to Graham in the third person to pass himself as an argument. M'lord is actually more appropriate Graham is a Baron

24 this is cool "this" is actually what's cool. I have an object of class Suitcase. Suitcase has a property "Person towner" A suitcase may have a method that depends on the owner So it could call "towner.canlift( this )" Yay! Reads like English! You can also type "this." to use the Power of Dot inside your own class. Saves typing.

25 Constructors One last thing: Constructors are functions that are called at the moment the object is made They are automatic and mostly just set up defaults, but can do whatever It's a method whose name is the class name and has no return type int mx; public SomeClass() { } mx = 5;

26 tostring() One more last thing This is a cute little automatic function to help debugging. Remember how println can turn numbers into a String? Anything with this function can do the same. You never actually type "tostring". If you do, you are bad and wrong. public String tostring() { } return "SomeClass: mx = " + mx;

27 Example: MainClass.java package MainPackage; public class MainClass { public static void main(string[] args) { SomeClass tanobject = new SomeClass(); System.out.println(tAnObject.WhatsX()); System.out.println(tAnObject); } } SomeClass.java package MainPackage; public class SomeClass { int mx; public SomeClass() { mx = 5; } } public int WhatsX() { return mx; } public String tostring() { return "SomeClass: mx = " + mx; } I'd like to just stop here and have y'all jump right in to the homework. The first Object lecture can be scary. If you are actually writing the Motorboat question that is secretly the exact same as the TV in Eclipse, just show it to me. Don't print it.

28 You can call yourselves programmers now Yay objects!

Java Programming. Computer Science 112

Java Programming. Computer Science 112 Java Programming Computer Science 112 Review: Problem solving Class 4 is the Whole Point of Programming. Is there any particular one you'd like to go through? If you are desperately confused still, now