elc 310 day 21. © 2004 pearson addison-wesley. all rights reserved10-2 agenda questions? capstone...

ELC 310

Day 21

© 2004 Pearson Addison-Wesley. All rights reserved 10-2

Agenda• Questions?• Capstone Proposals Overdue

4 Submitted 3 Accepted, 1 in negotiations Proposal should be in correct format (see guidelines in WebCT)

• Capstone progress reports overdue• Problem set 4 partially corrected

1 A, 1 B and 2 C’s Not doing some of the problems really hurts your score

• Problem set 5 Parts A & B Each worth 50 Points Due November 22 and Dec 2 respectively

• Exam #3 November 22 Chap 7, 8 & 9 25 M/C Available 7AM-7PM, Passwords will be e-mailed Sunday

• Discussion on Exception Handling

Chapter 10

Exceptions


Exceptions

• Exception handling is an important aspect of object-oriented design

• Chapter 10 focuses on:

the purpose of exceptions exception messages the try-catch statement propagating exceptions the exception class hierarchy GUI mnemonics and tool tips more GUI components and containers


Outline

Exception Handling

The try-catch Statement

Exception Propagation

Exception Classes

I/O Exceptions

Tool Tips and Mnemonics

Combo Boxes

Scroll Panes and Split Panes


Exception Handling

• An exception is an object that defines an unusual or erroneous situation Divide by zero Index out of bounds Can’t find a file Security violation

• Exceptions are “thrown” and “caught” Catching an exception allows you to recover from the problem

• An error is similar to an exceptions except that errors are generally unrecoverable

• There are 3 things you can do with an exception Ignore it Handle it where it happens Handle at some other point in the program


Uncaught (ignored) Exceptions• Uncaught exceptions cause program termination

Produces a message• What exception occured• Where the exception occurred

• Example Zero.java Exception in thread "main"

java.lang.ArithmeticException: / by zeroÏÏ§Ï at Zero.main(Zero.java:17)

Message includes • Information about the exception

– Method Exception.getmessage()• Call stack trace

– Method, file and line number– Method Exception.printStackTrace()

• Since the exceptions was not “caught”, the program terminated and the message was passed to the 0/S as output


Outline

Exception Handling



Exception Classes

I/O Exceptions


Combo Boxes



try-catch

• Try-catch allows the program to catch and handle an exception when it is thrown Fix the problem try { block of code}

catch (exception) { code to handle the exception}

• If the code in the try block does not produce an exception the catch block is skipped

try Block

catch handler

No exception

exception


Try-Catch

• Examples ProductCodes.java ProductCodes1.java

• Since the exceptions are caught and handled, the processing of the program does not terminate till the user explicitly terminates the program

• The “finally” clause Optional after a try-catch

try Block

catch handler

No exception

exception

FinallyBlock


Outline

Exception Handling



Exception Classes

I/O Exceptions


Combo Boxes




• If an exception is not caught and handled, control moves to the method that called the method that threw the exception.

• You can handle the exception at the higher level Called “propagating the exception” The exception will propagate ‘up’ the stack till

• It is handled

• Or, it forces the program to terminate

• Example Propagation.java ExceptionScope.java



• The exceptions moves up the stack of calling methods

doIt

helpMe

helpMe();

obj.doIt();

main

ExceptionthrownException

thrownExceptionThrown

Exceptionoccurred


Outline

Exception Handling



Exception Classes

I/O Exceptions


Combo Boxes



Exception Class Hierarchy

• Throwable class is parent of error and exception class

• You can define your own exceptions Inheriting from an Exception class


Creating your own exception

• Example CreatingExceptions.java OutOfRangeException.java

• Checked and Unchecked Exceptions Checked exceptions must be caught or explicitly thrown

by listing in the “throws” clause An unchecked exception requires no throws clause

• RunTimeException class (and it descendants) are the only unchecked exceptions in JAVA


Outline

Exception Handling



Exception Classes

I/O Exceptions


Combo Boxes



I/O Exceptions

• I/O is JAVA is treated as a Stream Ordered sequence of bytes from a source to a destination Read from input streams Write to output streams

• Three standard I/O streams System.in > Input (keyboard) System.out > Output (monitor) System.err >Output for error messages (monitor)

• I/O streams throws IOexception Checked exception

• Example TestData.java test.dat TestData1.java test2.dat

ELC 310

Day 23


Agenda• Questions?• Capstone progress due• Student Evaluation• Problem set 5 Parts A Corrected

Good results• Problem set 5 Part B

DUE Dec 2 • Exam #3 Corrected

Poor results 1 A, 2 C’s and 1 D

• Discussion on Tool tips and Mnemonics Advanced GUI components

• Tool Tips and Mnemonics• Combo Boxes• Scroll Panes and Split Panes

• Next is Recursion, generally a difficult subject for CS students Read ahead!


Tool tips and Mnemonics• Tool tip

Short Line of text that appears when ever the cursor is in top of the Swing component

Works with all Swing Components (J*) *.setTooTipText (“A message”);

• Mnemonic Hot key (ALT-”a key”) *.setMnemonic (‘C’); Underlines letter

• Disabling components *.setEnabled( false); Grays out component

• Examples Lightbulb.java LightBulbPanel.java LightBulbControls.java


Combo boxes

• Combo Boxes create “Drop Down” menus• Defined in JComboBox Class• Two ways to add items to the drop down

Using the constructor *.addItem(“the item”);

• Can also use ImageIcon

• Can be editable or uneditable Default is uneditable

• New object URL Url(“protocol”, “host”, ‘file”

• New interface AudioClip

• *.loop(); *.play(); *.stop();

• Example JukeBox.java JukeBoxControls.Java


Scroll Panes

• For Images and Information that is too large to fit in the assigned area

• Provides Scroll bars to navigate through the larger information or image

• Defined in JScrollPane class• Example

TransmitMap.java


Split panes

• Panel that displays twp components separated by a movable divider bar Horizontal

• Left, right

Vertical• Top, bottom

• Defined in JSplitPane class• Example

ListPanel.java PickImage.java


Summary

• Chapter 10 has focused on:

• the purpose of exceptions

• exception messages

• the try-catch statement

• propagating exceptions

• the exception class hierarchy

• GUI mnemonics and tool tips

• more GUI components and containers

elc 310 day 21. © 2004 pearson addison-wesley. all rights reserved10-2 agenda questions? capstone...

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