More Sophisticated Behavior

1
Chapter 5

• More Sophisticated Behavior

2
JAVA API Documentation

• A good programmer does not reinvent the wheel
• A good programmer uses what someone else has
  already written and debugged
• Java supplies us with a very rich class library
• You are not expected to know all the classes in
  the library, but you should know how to find out
  about a class

3
The String Class

• Lets look at the String classs on-line
  documentation
• String Class API Documention

4
Interface vs. Implementation

• The interface describes what a class does and how
  it can be used.
• The implementation of a class is the code that
  actually does the work.
• A good class will have a robust interface and
  allow the user of the class to perform all the
  necessary activities without needed to know how
  they were implemented.

5
String methods

• trim() removes extra whitespace from the
  beginning and end of the string
• startWith() indicates whether or not the string
  starts with the given prefix.
• equals() used to tell whether or not two
  strings are the same string, i.e. the same
  word(s)
• Note DO NOT USE to check string equality
• This does not do what you think it does
• split() splits the string into tokens using the
  given character as a delimiter

6
Packages and Import

• Import statements tell the Java compiler that we
  would like to have access to a particular class.
• It has the form
• import qualified-class-name
• import package-name.
• The qualified class name is the of its package,
  followed by a dot followed by the class name.

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Class Documentation

• Documentation of a class should include
• The class name
• A comment describing the overall purpose and
  characteristics of the class
• A version number
• The authors or authors name(s)
• Documentation for each constructor and method

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Method documentation

• The documentation for each constructor and method
  should include
• The name of the method
• The return type
• The parameter names and types
• A description of the purpose and function of the
  method
• A description of each parameter
• A description of the return type

9
javadoc

• BlueJ can create documentation for your projects
  from the tools menu.
• It will look for javadoc comments
• They start with / and end with /
• You can use some tags for key items
• _at_version
• _at_author
• _at_param
• _at_return

10
Public vs. Private

• The key word public and private are two of Javas
  access modifiers.
• In general, fields are private and methods are
  public
• There are many reasons why a method would be
  private
• There are almost no reason to make a field public

11
Access Modifiers

• Access modifiers allow Java to implement
  information hiding
• Information hiding is the idea that internal
  details of a class should be hidden from other
  classes.
• Information hiding is key to lowering the
  coupling between classes
• Coupling is the amount of reliance of a class on
  the implementation of another class.

12
Class variables and constants

• There are times when you want every object of a
  class to have a value
• The static key word declares a variable or
  constant to be shared by every object in the
  class.
• private static final int GRAVITY 3
• This example would give every object of this
  class GRAVITY.

13
Constants

• The key word static declares a constant or a
  variable as a class variable or constant.
• But what makes a variable into a constants?
• The key word final creates a constant
• private final int SIZE 10
• Constants must be initialized when they are
  declared and they cannot be changed