3.1 Objects

What's an object?

What's contained inside an object?

	objects contain variables (data, attributes)
	objects contain methods (operations, behaviors)

DEMO	(Book.java, create Book class)


3.4.2 Mutators and Accessors

How should the data inside an object be protected?

	instance variables should be declared private

	private String title;
	private int pages;

How can you access the data in an object if the data is private?

	mutators (setters) change the state of an object
	accessors (getters) read the state of an object

	public void setTitle(String title)
	public String getTitle()

Why do the setters need to check for valid values?


3.4.1 Constructors

How should constructors be implemented to avoid code duplication?

	constructors should call setter methods

	public Book(String title, int pages)


3.4.5 main

How many main methods can you have?

	one in each class

Why would you have a main method in each class you write?

	use main method for testing a class

DEMO	(test the Book class with main)


3.4.3 toString

Why do classes need a toString method?

DEMO	(add toString to Book class)
	public String toString()


3.4.4 equals

DEMO	(Library.java, create Library class)
	use array of Objects
	constructor
	add method
	main for testing

DEMO	(add toString method to Library class)

How would you modify add to prevent adding duplicates?

DEMO	(add duplicate objects)

Why do classes need an equals method?

DEMO	(add equals to Book class)
	public boolean equals (Object rhs)
	the parameter is always type Object


3.5.3 instanceof

DEMO	(Video.java, add Video object to library)
	use existing Video class

How do you make equals compare Books and Videos?

	use instanceof to avoid ClassCastException
	equals must work for any object passed in
	    if (rhs instanceof Class) {


3.6 Packages

What is the purpose of packages?

	packages are used to organize collections of classes

How do you put classes you write into packages?

DEMO	(put Book, Video, Library classes into packages)
	put Library in library package
	put Book/Video in library.holdings package
		package library;
		package library.holdings;

Why doesn't Library compile?

DEMO	(add imports for Book and Video)
	import library.holdings.Book;

Why does Library still not compile?

DEMO	(put Book/Video in correct directory)
	javac library/Library.java

When do you need to use -classpath with javac?

	when the current directory is not the root of the packages
	javac -classpath ../ Library.java

What happens when you try to run the Library class?

	java Library

Where does the Library class need to located?

	java library.Library

When do you need to use -classpath with java?

	java -cp pathname library.Library