Intro to Computer Science Class #2 Administrative Details and Introduction to Objects Instructor: Ms. Catherine Stocker Teaching Assistants: Alex, Katie, Siraaj, Isaiah, Allison, Thibault University of Pennsylvania 30 January 2008

Today’s Agenda New Teaching Assistants Discussion (Reaction paper) Class Rules What is Java? BotPlay

New Teaching Assistants Let’s all introduce ourselves one more time.

Discussion Let’s talk about the reaction paper.

Attendance/Participation I will take attendance at the beginning of every class. –Don’t be late –Don’t be disruptive –Do your work If you are late or absent, bring me a note. Questions and discussion are highly encouraged!

Stuff You Should Already Know DON’T COPY CODE –It’s easy to spot. –It only hurts you – the material builds on itself. –When does giving/getting help cross the line to cheating? Course website: –I will also try to post other helpful links on the resources page of the course website. resources page

General Layout of Class 1:30-1:45 – Attendance and Discussion 1:45-2:30 – Lecture 2:30-2:40 – Short Break 2:40-3:30* – Lab Work (*Sometimes 30 min guest speakers) I will teach for this class and the next, then the teaching assistants will start running the class, while I supervise and help out. You will be assigned a programming assignment each week which you are expected to turn in before class the next week.

What to do if you’re stuck… 1)Try things out! Don’t be scared of the computer. (Just make sure to have a backup copy of your work!) 2)Check out the resources pageresources page 3)Post to the bulletin board!bulletin board 4)Come talk to us (before/after class). 5) me

What is Java? A high-level, object-oriented, programming language Language: –A way for people to communicate… With Humans: Use human languages (English, Spanish, Chinese, …) With Computers: Use programming languages (Java, C++, Python,...) –Made of vocabulary and syntax (rules for how to arrange the vocabulary)

What is Java? A high-level, object-oriented, programming language Language: –A way for people to communicate… With Humans: Use human languages (English, Spanish, Chinese, …) With Computers: Use programming languages (Java, C++, Python,...) –Made of vocabulary and syntax (rules for how to arrange the vocabulary)

What is Java? A high-level, object-oriented, programming language Language: –A way for people to communicate… With Humans: Use human languages (English, Spanish, Chinese, …) With Computers: Use programming languages (Java, C++, Python,...) –Made of vocabulary and syntax (rules for how to arrange the vocabulary)

What is Java? A high-level, object-oriented, programming language Language: –A way for people to communicate… With Humans: Use human languages (English, Spanish, Chinese, …) With Computers: Use programming languages (Java, C++, Python,...) –Made of vocabulary and syntax (rules for how to arrange the vocabulary) English: –Vocabulary: Anything in an English dictionary. –Syntax: How to arrange noun, verb and prepositional phrases, etc

What is Java? A high-level, object-oriented, programming language Language: –A way for people to communicate… With Humans: Use human languages (English, Spanish, Chinese, …) With Computers: Use programming languages (Java, C++, Python,...) –Made of vocabulary and syntax (rules for how to arrange the vocabulary) English: –Vocabulary: Anything in an English dictionary. –Syntax: How to arrange noun, verb and prepositional phrases, etc Java: –Vocabulary and Syntax: Keywords, and rules for arranging those key words, that you will learn in this class! »You learned some keywords already: int, char, boolean, String »You also already learned some syntax: int a = 5; boolean b = true;

What is Java? A high-level, object-oriented, programming language High-level: High-level of abstraction Abstraction: Hiding unimportant details –“The ball broke the window.” Does it matter what kind of ball? What color? The speaker abstracted away unimportant details of the ball. –Similarly in programming languages If we programmed in “machine language” (a lower-level language) we would have to write it specifically for that computer. Programming in Java, we are choosing to ignore details about any specific computer and focus on what all computers have in common. This program will then be translated by another program to a language specific to that machine.

What is Java? A high-level, object-oriented, programming language High-level: High-level of abstraction Abstraction: Hiding unimportant details –“The ball broke the window.” Does it matter what kind of ball? What color? The speaker abstracted away unimportant details of the ball. –Similarly in programming languages If we programmed in “machine language” (a lower-level language) we would have to write it specifically for that computer. Programming in Java, we are choosing to ignore details about any specific computer and focus on what all computers have in common. This program will then be translated by another program to a language specific to that machine.

What is Java? A high-level, object-oriented, programming language Hardware (CPU) (electrical impulses) Machine Language (0’s and 1’s) Bytecode Java Source Code (i.e. what you’ve written, held in a.java file) Compiler compiles (translates) it into bytecode (held in a.class file) Java Virtual Machine figures out how to run it on your computer

What is Java? A high-level, object-oriented, programming language Object-Oriented: Thinking about your program as a collection of objects that have a state and a behavior. Similar to the way we think about the world. –Example: Object = Horse State = name, hungry, mph Behavior = eat, walk, gallop, jump Other ways to think about your program: functional, procedural…we won’t look into these Horse name hungry mph horsey yes 5

Other Objects

How We Define An Object Depends On How We’re Going To Use It Abstract away the unnecessary details – only keep the important (relevant to the program) ones in the state. Program: Keep track of baseball stats –Object: Baseball Player –State: name, G, AB, R, H, HR, on base, at bat, –Behavior: run, walk, hit ball, slide, batting Baseball Player name G AB Ryan H R H HR onBase atBat RBI 3 no 353

How We Define An Object Depends On How We’re Going To Use It Abstract away the unnecessary details – only keep the important (relevant to the program) ones in the state. Program: Simulate how athletes lifestyles affect their popularity with fans, salary and injury rate –Object: Athlete –State: name, sport, salary, days injured, popularity –Behavior: negotiate contract, party, complain, retire Athlete name Ryan H sport baseball salary 900,000 daysInjured 25 popularity high

Other Objects

How Do We Translate What We’ve Talked About Into Java? class Athlete { String name ; String sport; int salary; int daysInjured; String popularity; Athlete(String n, String s) { name = n; sport = s; salary = 0; daysInjured = 0; popularity = “average”; } void negotiateContract(int newSalary) { salary = newSalary; } void party() { daysInjured = daysInjured + 10; } void complain() { popularity = “low”; } void retire() { salary = 0; popularity = “high”; } void printStates() { System.out.println(“name: “ + name + “, sport: “ + sport + “, salary: “ + salary + “, daysInjured: “ + daysInjured + “, popularity”); } }

How Do We Translate What We’ve Talked About Into Java? class Athlete { String name ; String sport; int salary; int daysInjured; String popularity; Athlete(String n, String s) { name = n; sport = s; salary = 0; daysInjured = 0; popularity = “average”; } void negotiateContract(int newSalary) { salary = newSalary; } void party() { daysInjured = daysInjured + 10; } void complain() { popularity = “low”; } void retire() { salary = 0; popularity = “high”; } void printStates() { System.out.println(“name: “ + name + “, sport: “ + sport + “, salary: “ + salary + “, daysInjured: “ + daysInjured + “, popularity”); } } The state or instance variables an object will have.

How Do We Translate What We’ve Talked About Into Java? class Athlete { String name ; String sport; int salary; int daysInjured; String popularity; Athlete(String n, String s) { name = n; sport = s; salary = 0; daysInjured = 0; popularity = “average”; } void negotiateContract(int newSalary) { salary = newSalary; } void party() { daysInjured = daysInjured + 10; } void complain() { popularity = “low”; } void retire() { salary = 0; popularity = “high”; } void printStates() { System.out.println(“name: “ + name + “, sport: “ + sport + “, salary: “ + salary + “, daysInjured: “ + daysInjured + “, popularity”); } } The behaviors or methods of the object. They can change the state/instance variables or show us the state when we ask.

How Do We Translate What We’ve Talked About Into Java? class Athlete { String name ; String sport; int salary; int daysInjured; String popularity; Athlete(String n, String s) { name = n; sport = s; salary = 0; daysInjured = 0; popularity = “average”; } void negotiateContract(int newSalary) { salary = newSalary; } void party() { daysInjured = daysInjured + 10; } void complain() { popularity = “low”; } void retire() { salary = 0; popularity = “high”; } void printStates() { System.out.println(“name: “ + name + “, sport: “ + sport + “, salary: “ + salary + “, daysInjured: “ + daysInjured + “, popularity”); } } Ryan Howard is not the only Athlete. He is one of many. The “blueprint” for an Athlete is laid out in this class. An object is an instance of a class. The class tells us how to set up the “state box” we’ve been drawing. But we don’t actually draw it until we create an object.

How Do We Translate What We’ve Talked About Into Java? class Athlete { String name ; String sport; int salary; int daysInjured; String popularity; Athlete(String n, String s) { name = n; sport = s; salary = 0; daysInjured = 0; popularity = “average”; } void negotiateContract(int newSalary) { salary = newSalary; } void party() { daysInjured = daysInjured + 10; } void complain() { popularity = “low”; } void retire() { salary = 0; popularity = “high”; } void printStates() { System.out.println(“name: “ + name + “, sport: “ + sport + “, salary: “ + salary + “, daysInjured: “ + daysInjured + “, popularity”); } } The constructor. This is where we set up the starting state by assigning values to the instance variables.

Now… Let’s play with that Athlete code. BotPlay (

Later… Write a class of your own. Include at least 2 instance variables and 2 methods that change those instance variables. Write down something you were confused about from class and a short explanation about what confused you (1-3 sentences).