cse 1020: exceptions and a multiclass application

CSE 1020: Exceptions and A multiclass application

Mark Shtern

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Summary

• Collection Framework– List– Map– Set

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Final Exam

• Written Component– UML– Aggregation and Composition– Collection Framework– Inheritance (interfaces, abstract and concert

classes)– Exception and error handling

• Lab component– Multiclass application

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Sources of Errors

• The programmer• The End-User• The Runtime Environment

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Exception Handling

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Sources

Error Valid Operation?

Logical Error

Exception

Caught?Handler

Runtime Error

Yes

Yes

No

No

The Delegation Model

• Handle or delegate policy– Detects an invalid operation in a method – Throws an exception– Searches the method for an exception handler– If the handler found then control is given to the it– If no, the search is transferred to the caller of the

method– If no method can handle the throw exception, a

runtime error occurs and the program terminated

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Basic try-catch Construction

try{ code fragment} catch (SomeType e) {

exception handler}

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Handling Multiple Exception

try{ code fragment} catch (Type-1 e){} catch (Type-3 e){} catch (Type-3 e)

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Other construction

• Finally• Nested try-catch

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The Throwable Hierarchy

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Object Oriented Exception Handling

• The substitutability principle– When a parent is expected, a child is accepted

• Throwable methods– getMessage()– printStackTrace()

• Explicit exception creation and throw ArithmeticException ae = new

ArithmeticException() throw ae;

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Building Robust Apps

• Validation versus Exception– Defensive Programming– Exception-Based programming

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Exercise 11.1

• Write a code fragment that performs the same function as the statement below without using the crash method

Toolbox.crash(amount < 0, “A negative amount!”);

Exercise 11.2

• Locate the error and specify if it is compile-time, runtime, or logic

try{ // some code }catch (java.io.IOException e){ // some code }catch (java.io.FileNotFoundException e){ // some code }

Exercise 11.3

• Explain what is wrong with the following

try{ // some code }catch (Exception e){}

Exercise 11.4

• Critique the following and compare to the previous exercise

public static void main (String[] args) throws Exception

A Multiclass Application

• The abstract foods company• UML see on page 448

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Classes• AbstractFods– Inventory– Journal– Contact

• Item• Fresh• Trx• Contact• Supplier– Catalog

• Client

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Exception Examples

• The program reads a string of two slash-delimited integers, extracts two integers, divides them, and outputs their quotient.

• Modify the program to handle input errors

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Summary

• Exception• throw vs throws• Catch• Finally• Check vs Uncheck

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I/O Stream

• Keyboard input– Standard input– Keyboard source– Program data sink– Channel stream

• InputStream

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System class

• in• out

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InputStream

InputStream keyboard = System.in;int input = keyboard.read();

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Input Stream

BufferedReader buffer = new BufferedReader (new InputStreamReader(System.in));

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File input

• Open Stream BufferedReader filer = new BufferedReader (new

InputStreamReader(new FileInputStream (fileName)));• Reading for (String line = filer.readLine(); line != null; line = filer.readline()) {

//process}

• Close Stream filer.close();

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Screen Output

• Standard Output• Output Stream• Standard Error• PrintStream

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Serialization

java.io.objectOutputStreamFileOutputStream fos = new FileOutputStream

(fileName);ObjectOutputStream oos = new

ObjectOutputStream(fos);oos.writeObject(gc);oos.close();

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Deserialization

java.io.ObjectInputStreamFileInputStream fis = FileInputStream(filename);ObjectInputStream ois = new

ObjectInputStream(fis);Object obj = ois.readObject();ois.close ();

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Date

• Date• Calendar• Date/Format• SimpleDateFormat

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Exercise 10.1

• Determine the interface that should be used for each of the following collections– The names of all students registered in a course– The letter grades obtained in a course– The names of your contacts and the telephone

number of each– The reserved words in Java

Exercise 12.2

• Write a program that– Creates an Item instance named Tuna with price

$2.45– Purchases 200 units for a total of $250– Sells 50 units– Sells 25 units for a total of $30– Purchases 100 units for a total of $175– Outputs unit cost price

Exercise 12.3

• Write a program that– Creates a Fresh instance called “Pacific Salmon”, with any

item number, a price of $20, and an expiry date three weeks from now

– Creates a Fresh instance called “Atlantic Salmon”, with the same item number as above, a price of $25, and an expiry date 20 days from now

– Outputs the return of the equals method invoked on one passing the other as argument

– Outputs the return of the toString method for the two items