Review for Exam1 221

• Java review

• Most of this was from looking a code

• PhoneDirectory code was almost like the DVD code

• How to write a class for a single object

• PDEntry

• DVDEntry

• constructors

• mutators and accessors

• toString method so object could be output

• How to write a class for an array of objects

• how to declare a constant

• how to read from a file and write to a file

• how to add another object to the array

• how to find the data of an item, given the key

• how to throw and catch exceptions

• when to use private methods instead of public

• How to access components of an object stored in an array of those objects

• How to write a client for the array of objects class

• Static methods, when to use

• How to use the array of objects as an argument for a method

• Using a menu to let the user choose an option

• How to stub in un implemented methods

Exceptions

• Know something about the exception hierarchy

• Know the difference between checked and unchecked exceptions

• Know what the stack trace is

• Know how exceptions that are not caught are propagated back to the calling method

• Know when to use a throws clause

Big-O notation

• We did not look at the formal definition

• Know that Big-O is a way to relate execution timeT(n) with input size n

• Know the common growth rates, and their relative order

• Inheritance

• Why is it important?

• How does it work?

• Superclass is more general, subclass is more specialized

• Inheritance is used with an is-a relationship, not a has-a relationship

• Know the difference between the protected access specifier and private

• Understand about constructor chaining (call the superclass with the keyword super)

• Know what overriding is and how it works

• Know what polymorphism is, and how it can be implemented

• Understand that a reference variable might refer to an object whose type is a subtype

• So the reference variable and objected referred to may not be the same type

• The constructor called determines the object’s type

• The variable declaration determines the reference variable’s type

An abstract class is a class which has one or more abstract methods

• An abstract method is a method that is not implemented

• Abstract classes may not be instantiated, but can have instance variables and implemented methods

The Object class

• All other classes are derived from the Object superclass

• Useful methods include Object clone( ), boolean equals(Object) and String toString

• When these methods are overriden the the Object type must be downcast to the type you are working with

• Cloning

• Visibility