CSE 113 Introduction to Computer Programming

CSE 113Introduction toComputer Programming Lecture slides for Week 2 Wednesday, September 7th, 2011 Instructor: Scott Settembre

Section 1 Recitations (Labs) University at Buffalo: CSE 113 Instructor: Scott Settembre

Labs Begin This Week • Go to Bell hall [next to Student Union] Room 340. • There is key card access that your card won’t open, so you will need to wait for the TA sometimes to show up to let you in. • If you queue in the hall, please be respectful of the offices and classrooms around you. • Please go to your lab. • It is mandatory. • Attendance counts towards your grade. • There is an end of class assessement/quiz. University at Buffalo: CSE 113 Instructor: Scott Settembre

What do I do in lab? • You will be doing the chapters from the Greenfoot book, step by step. • Do each exercise. • You do not need to record your answers. • The assessment/quiz at the end of the class may require you to answer some questions about those exercises. University at Buffalo: CSE 113 Instructor: Scott Settembre

When I am done, what do I do? • After you go through the chapters that you need to cover, you will: • Work on your project. • Take the assessment/quiz at the end of class. University at Buffalo: CSE 113 Instructor: Scott Settembre

Can’t I take the quiz and leave? • No. • Use the two hours to experiment and work on your project. • If you at some point become done with your project, then work on it more. • Think of your project as an art piece, Leonardo da Vinci said that “art is never finished, only abandoned.” • When your project is due, that is when you are done!  University at Buffalo: CSE 113 Instructor: Scott Settembre

For the First Week in Recitaiton • For the week of September 7th • Please read chapter 1 and chapter 1 exercises. • Please read chapter 2 and chapter 2 exercises. • Please finish by taking the assessment/quiz. • At that point, for this week only, you can leave early! • The first project will be assigned next week. University at Buffalo: CSE 113 Instructor: Scott Settembre

Section 2 Greenfoot – Interface University at Buffalo: CSE 113 Instructor: Scott Settembre

Demonstration • You will become more familiar with the interface when you go hands-on with the book in the lab. • I will demo the interface here to show you around. University at Buffalo: CSE 113 Instructor: Scott Settembre

Section 3 Greenfoot – Chapter 2 University at Buffalo: CSE 113 Instructor: Scott Settembre

Chapter 2 • In this chapter you will learn: • How to start writing code. • How to find out what methods you can use. • What an “if”-statement is! (Probably the most important control statement you will learn.) University at Buffalo: CSE 113 Instructor: Scott Settembre

What is “inheritance”? • It is the “is-a” relationship between classes • For example: • “A dog is-a mammal” • “A chiuaua is-a dog” • This means that a dog “inherits” all the features that a mammal may have. • “Sub-classes” (see last weeks notes) inherit their properties and methods from their “Super-classes” University at Buffalo: CSE 113 Instructor: Scott Settembre

Crab and Animal classes • Notice the arrow direction in the Actor classes tree. • A crab is-a animal. • An animal is-an actor. • Thus a crab is-a actor too! University at Buffalo: CSE 113 Instructor: Scott Settembre

Classes can inherit methods • The animal class has a method called “act”, so that means that the crab class will also have that method. University at Buffalo: CSE 113 Instructor: Scott Settembre

University at Buffalo: CSE 113 Instructor: Scott Settembre

What do the methods do? • There are many methods in the animal class: • “act” method, does nothing. • “move” method, moves the actor in a forward direction. • “turn” method, rotates the actor a number of degrees specified in the parameter. • “atWorldEdge” method, returns a boolean value indicating if the actor is at the edge of the world. • What we will do is make the “act” method do something, like call the “move” method. University at Buffalo: CSE 113 Instructor: Scott Settembre

Writing code • To begin writing code, let Greenfoot do the framework for you. • Double-click on the class to get the editor. • Go to the already formed “act” signature. • We can add “move();” within the brackets { } to make it move. University at Buffalo: CSE 113 Instructor: Scott Settembre

Note: brackets and semicolons • You need to adhere to a specific “syntax”. • When you write English, we need to use “,” and “.” appropriately otherwise the reader will misread what you have written. • It is the same thing with Java, you need to use the “{“, “}” and “;” correctly or it will not understand you. University at Buffalo: CSE 113 Instructor: Scott Settembre

Semicolons • A semicolon “;” indicates an end of a command. • It is similar to a “.” at the end of an English sentence. University at Buffalo: CSE 113 Instructor: Scott Settembre

Brackets and code blocks • The instructions between a set of brackets is called a “code block” or the “body” of a method. • You must match each “{“ with a “}” University at Buffalo: CSE 113 Instructor: Scott Settembre

Syntax errors: Ooops, I messed up?! • This will happen a lot. • Greenfoot with alert you to a mistake. • You can see if you have any syntax mistakes by compiling or running your code. • Note: Sometimes you will have two or more mistakes, causing your code to compile/run, but not work properly. This is not a syntax error, this is a code error. University at Buffalo: CSE 113 Instructor: Scott Settembre

To be continued on Friday University at Buffalo: CSE 113 Instructor: Scott Settembre

CSE 113 Introduction to Computer Programming