1. AP Computer Science
Mr. Wortzman

2. Lightbot/byob debrief
With your table group, discuss the following:
Did you enjoy these activities? Why or why not?
What did you find most challenging about these activities?
Were there times in LightBot that you had to completely reset your work and try again? If so, why?
Did you ever end up with code in BYOB that did not exactly match the solution? What does that tell you about coding?
Why did we have to give instructions to LightBot or Alzono in the format we did (as opposed to typing English commands)?

3.
Introduction to Java

4. A Brief History
Originally released in 1995 by Sun Microsystems (now a subsidiary of Oracle)
Designed to write programs for “embedded devices,” specifically TVs
As such, Java is designed for small, lightweight programs
Turns out, this makes it ideal for writing programs for the internet as well

5. Key Characteristics “Write-once, run anywhere”
Java programs are compiled to bytecode rather than machine code
The bytecode can be executed by any Java VM on any computer
Automatic memory management
Java tracks what memory is currently in use and reclaims memory that is no longer needed
Other languages (such as C/C++) require the developer to track this himself
Object-oriented

6. Actually Writing Java Programs
Writing and running programs requires a number of tools:
An editor to write and edit the code
A compiler to translate the program from Java code to Java bytecode
A virtual machine or runtime to translate the bytecode to machine code, which the computer can execute
A debugger to help track down and fix problems

7. Actually Writing Java Programs
Edit
Compile
Run
Debug

8. Actually Writing Java Programs
Edit
Compile
Run
Debug
Java Code
Compiler
Java Bytecode

9. Actually Writing Java Programs
Edit
Compile
Run
Debug
Java VM
Machine Code
Execute
Java Bytecode

10. Actually Writing Java Programs
We could just use notepad (or any other text editor) and command-line tools
javac (compiler) and java (vm)
This is very simple and lightweight, but has a lot of drawbacks
Very little confirmation we’re doing things right
Introduces multiple potential points of failure
Instead, we will use an integrated development environment (IDE) called jGRASP

11. jGRASP Walkthrough

12. Object-oriented Programming
OOP is based on four main concepts:
Objects that represent actors in a program
Messages that trigger behavior or request data from objects
Methods that perform some set of actions
Classes that define state and behavior shared by a set of objects

13. Your First Java Program
public class FirstProgram { public static void main(String[] args) { System.out.println(“Hello, world!”); }

14. Your First Java Program
Class
Method
public class FirstProgram { public static void main(String[] args) { System.out.println(“Hello, world!”); }
Object
Message

15. Writing Java Programs
Every Java program consists of one or more classes
At least one of these classes must have a “main” method
The “main” method defines where the program starts

16. Java Syntax
Java programs are made up of one or more classes, each with one or more methods, each of which consists of one or more statements
Statements are like blocks in BYOB
public class Program {
public static void main(String[] args) {
int i = 5;
System.out.println(“Hello!”);
System.out.println(i + 2); }
Class
Method
Statement
Statement
Statement

17. Java Syntax General form: public class ClassName {
public static void main(String[] args) {
statement1;
statement2;
statement3;
...
statementN; }

18. Our First Object A PrintStream called System.out
Short version: System.out is used to output text to the console
Two primary methods used to print output:
print
println

19. Writing Java Programs
Java has many, many predefined classes and objects that provide common behavior
System.out from our program is one example
This prevents Java developers from having to constantly “reinvent the wheel”
These classes and objects (collectively referred to as the “Java API”) are documented on the Java website:
Bookmark this page– it will be your Java bible

20. Java API Walkthrough

21. Java API Scavenger Hunt
Use the Java API to answer the following questions (you may use Bing/Google to help you as well):
What does a String represent in Java?
How do you get a small portion from a String?
How do you find the square root of a number in Java?
What is the difference between print and println in PrintStream?
What types of things can you generate randomly?
What types of things can you read from a Scanner?
What is a Float?
How can you determine if a character is uppercase?

22. Strings A sequence of characters is called a string
Strings are usually, but not exclusively, used for input and output
Strings in Java are enclosed in double-quotes (“string”)
Identify the string in System.out.println(“Hello, world!”);
String is an example of a pre-defined Java class

23. Our First Object
Exercise 1: Write a Java program to print the following to the console:
My name is <your name>
and I love Java!!
Exercise 2: Write a Java program to print “Go Issaquah Eagles” (all on one line, without the quotes) to the console. Use 3 separate statements.

24. Documentation
Documentation refers to elements of code that help a reader understand what’s going on
Comments are the primary, but not the only, form of documentation
Two types of comments in Java:
Single-line comments:
// this is a single-line comment
Multi-line (or C-style) comments:
/* this is a
multi-line comment */
Comments are ignored when compiling and executing code

25. Documentation Use comments frequently to:
Describe the basic, high-level behavior of a chunk of code
Explain anything potentially unclear or tricky
Explain why you chose to do something a certain way if there were multiple options
Etc.
You should also make your code self-documenting by:
Choosing descriptive, readable names
Using line breaks
Indenting/aligning things well

26. Identifiers
The names of classes, methods, variables, etc. are referred to as identifiers
Identifiers can consist of letters, digits, or underscores
The first character cannot be a digit
Identifiers should be descriptive, but not unwieldy
Bad: x (non-descriptive), myVariableThatIsUsedToCountSomething (too long)
Good: count, numTries, xCoordinate

27. Identifiers Java has certain conventions for identifiers
Identifiers are always a single word (no spaces)
Class names should start with an uppercase letter, and use an uppercase letter to indicate word breaks
e.g. String, PrintStream, MixedFraction
This is called Pascal casing
Variables/methods/etc. should start with a lowercase letter, and be cased similarly
e.g. size, numLoops, firstName

28. Methods A method is a defined behavior of a particular class
Passing a message in Java is referred to as calling (or invoking) a method
Method calls have the following parts:
The target or receiver of the message is the object whose behavior we want to trigger
The method name of the method we want to call
If necessary, some number of arguments
Arguments provide additional information needed by the method

29. Anatomy of a Method Call
System.out.println(“Hello, world!”);
Target or Receiver
Argument
Method Name

30. Static Methods
A static void method is a simple collection of statements
We’ll learn precisely what those modifiers mean soon
Where have you seen them before?
Three phases to using a static method:
Design: decide what the method will do; write an algorithm
Define: write the code to give your method a name and describe what it does
Call: use the method in main (or another method)

31. Static Methods When should we define a new method?
Ideally a method should be:
Reusable: methods should consist of code we’ll need more than once
Specialized: each method should perform a specific subtask
Modular: each method should be (more or less) self-contained
We should not use methods to:
Give a single statement a new name
Combine unrelated statements

32. Declaring Static Methods
Syntax:
public static void <name>() {
<statement>;
... }

33. Declaring Static Methods
Example: public static void printGreeting() {
System.out.println(“Hello, world!”);
System.out.println(“Welcome to my program.”); }

34. Calling Static Methods
Syntax:
<name>();
Example:
public static void main(String[] args) {
printGreeting();
System.out.println(“This is fun!”); }
Output:
Hello, world!
Welcome to my program.
This is fun!

35. Static Methods
Exercise 1: Write a program that prints your name in the following forms:
FirstName LastName
FirstName MiddleName LastName
LastName, FirstName
LastName, FirstName MiddleName
Exercise 2: Rewrite the above program using static void methods.

36. Procedural Decomposition
Imagine an algorithm for making cookies:
Making sugar cookies
Mix the dry ingredients
Cream the butter and sugar
Beat in the eggs
Stir the dry ingredients into the wet
Set the oven to 400°
Put the cookies in the oven
Bake for 10 minutes
Remove the cookies from the oven and allow them to cool
Mix the ingredients for the frosting
Frost the cookies

37. Procedural Decomposition
What if we were making a double batch?
...
Set the oven to 400°
Put the first batch of cookies in the oven
Bake for 10 minutes
Remove the cookies from the oven and allow them to cool
Put the second batch of cookies in the oven

38. Procedural Decomposition
This algorithm is unstructured, making it hard to follow
It’s also redundant in the double batch case
We can do better!
Procedural decomposition: breaking a large task down into a number of smaller, self-contained subtasks

39. Procedural Decomposition
We can decompose our recipe into three subtasks:
Making sugar cookies
Make the batter
Bake the cookies
Frost the cookies
The first subtask is defined as:
Make the batter
Mix the dry ingredients
Cream the butter and sugar …

40. Procedural Decomposition
This also allows us to eliminate redundancy in our double batch recipe:
Making sugar cookies (double batch)
Make the batter
Bake the cookies (batch #1)
Bake the cookies (batch #2)
Frost the cookies (batch #1)
Frost the cookies (batch #2)

41. Calling Methods You can also call methods from other methods:
public static void startProgram() {
printGreeting();
System.out.println(“\nAre you ready to begin?”); }

42. Method Call Control Flow
The point at which a method is called is referred to as the call site
The method that is being called is the callee
The method doing the calling is the caller
When a method is called, the program:
Pauses execution at the call site
Begins executing the callee from its beginning
When execution of the callee is complete, control returns to the caller at the next statement/expression after the call

43. Method Call Control Flow
Example:
public static void main(String[] args) {
printGreeting();
startProgram(); }
System.out.println("Hello, world!");
System.out.println("Welcome to my program.");
System.out.println("This is fun!");
printGreeting();
System.out.println(“Are you ready to begin?");

44. Escape Sequences Some characters cannot be included in a string
Can you think of any examples?
", newline
To include these (and other special characters) we use an escape sequence

45. Escape Sequences Escape sequences are prefixed with a \ (backslash)
\n – newline
\" – quotation mark
\t – tab
\\ - backslash
Why do we need this one?

46. Escape Sequences System.out.println("\ta\tb\tc");
Exercise 1: What output is produced by these statements? (Do NOT use your computer!)
System.out.println("\ta\tb\tc");
System.out.println("\\\\");
System.out.println("'");
System.out.println("\"\"\"");
System.out.println("C:\nin\the downward spiral");
Exercise 2: Write a Java statement to produce this output:
/ \ // \\ /// \\\

47. Static Methods Case Study
Exercise: Write a program to produce these figures. Reduce redundancy as much as possible by using good functional decomposition.

48. Procedural decomposition practice
Exercise: Write a program to print out the lyrics to "The Old Lady Who Swallowed a Fly" (lyrics can be found at
Use good procedural decomposition and eliminate as much redundancy from the program as possible.
Also, ensure that main is a concise summary of the program's behavior.
Turn in this program when it is complete.