CP4

9/27/21

*EXCEPTION

_Software will often be used in conditions that designer cannot precisely anticipate

Ex:

+A user might ender data that is incorrect

+A user programmer might create or manipulate objects in incorrect ways

+Programmatic operations might fail

+System errors might occur

_Technique for highlighting errors

+Sysout(ERROR_MESSAGE);

+System.err.println(ERROR_MESSAGE);

+Return a value that indicate an error

+System.exit();

_Syntax

try {

catch {

finally {

9/29/21

_UML access

+public, -private, #protected, ~package (default visibility)

_Classes as contracts

+Superclass makes certain promises about available methods and instance variables. These promises must be kept by all child classes. But the implementation of these promises can be overridden.

+Sometimes a superclass needs to make a promise but not implementation => use abstract: abstract class can not be instantiated

_Abstract class

+A class that extends an abstract class must: implement all abstract methods or also be an abstract class.

+Properties: Must provide constructors: private and protected constructors, child classes can reference these with super

+Provide as many as method implementations as possible

_”Multiple inheritance”

+A clone of an object is equal in content but distinct in memory footprint

+Clone is not just a copy of object’s memory, but of all of its component objects (and their components, etc.)

*Java restriction:

+If a class inherits from Cloneable class, it can not inherit from other classes

The interface

+An interface defines no implementation – only a set of abstract methods

+A class can implement any number of interfaces