Download ppt - kaist

Programming Languages
(ICE 1341)
Lecture #21
May 21, 2004
In-Young Ko
iko .AT. icu.ac.kr
Information and Communications University (ICU)
May 21, 2004
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
1
Announcements

Project Presentations



Dater & Time: Thursday May 27th, 7:30PM – 9:30PM
10 minutes for each team (in English)
Final Exam:



Dater & Time: June 4, 2004 11:00AM-12:00PM
A hand-written cheat sheet is allowed
Chapters that will be covered:




May 21, 2004
Chapter 8 – 11
Chapter 12 except 12.7, 12.8 and 12.9
Chapter 13 except 13.7
Chapter 14
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
2
Review of the Previous Lectures

Semaphores






Synchronization Problems
Dining Philosophers Problem
Monitors
Message Passing
Java Threads
Statement-Level Concurrency
May 21, 2004
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
3
Exception Handling
30

OPEN (UNIT=10, FILE='data.txt', STATUS='OLD')
READ(10, *, END=40, ERR=50) NUM
…
GOTO 30
FORTRAN
Exception: An unexpected condition that is raised (thrown)
during program execution




Hardware Detectable Exceptions: e.g., Floating-point overflow, I/O
errors
Software Detectable Exceptions: e.g., Array subscript range errors,
null pointer exceptions
Exception Handling: The special processing that may be
required after detection of an exception is called
Exception Handler: The exception handling code unit
May 21, 2004
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
4
Exception Handling Example
void fileCopy(String file1, String file2) {
try {
FileInputStream in =
new FileInputStream(file1);
FileOutputStream out =
new FileOutputStream(file2);
int data;
while ((data = in.read()) >= 0)
out.write(data);
} catch (FileNotFoundException e1) {
System.err.println
(“Cannot open input or output file.”);
} catch (IOException e2) {
System.err.println
(“Cannot read or write data.”);
}
}
Java
May 21, 2004
May throw the File Not
Found Exception
May throw the IO
Exception
Exception Handlers
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
5
Exception Descriptions in the Java
API Manual
May 21, 2004
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
6
Exception Handling Control Flow
Main Program
Control
Main Program
Control
Catching the
exception
Exception
Uncaught
exception
Exception
Exception
Handler
Continuation
of the main
program
May 21, 2004
Operating
System
Discontinuation
of the main
program
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
7
Advantages of Built-in Exception
Handling


Programmers do not need to explicitly define,
detect, and raise exceptions
Exception propagation allows a high level of
reuse of exception handling code
* AW Lecture Notes
May 21, 2004
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
8
Exceptions in Java

All exceptions are objects of classes that are
descendants of the Throwable class
Serious problems that a
user program should not
try to catch
e.g., Heap overflow
Program errors
e.g., Array index
out-of-bound, Null
pointer exception
Exception
…
… IOException
RunTimeException
Unchecked Exceptions
• User programs are not
required to handle them
• The compiler do not
concern them
May 21, 2004
Error
… FileNotFoundException
MyIOException
(User-defined Exception)
Checked Exceptions
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
9
Exception Handling in Java
void fileCopy(String file1, String file2) {
 Exceptions cannot be
try {
disabled
FileInputStream in =
new FileInputStream(file1);
 Binding Exceptions to
FileOutputStream out =
Handlers – An exception
new FileOutputStream(file2);
is bound to the first
int data;
handler with a parameter
while ((data = in.read()) >= 0)
out.write(data);
is the same class as the
} catch (FileNotFoundException e1) {
thrown object or an
System.err.println(“Can’t open a file.”);
ancestor of it
} catch (IOException e2) {
System.err.println(“Can’t read or write.”);  Specify code that is to be
} finally {
executed, regardless of
in.close();
what happens in the try
out.close();
construct
}
}
May 21, 2004
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
10
Exception Propagation in Java
void fileCopy(String file1, String file2)
throws FileNotFoundException,
IOException {
FileInputStream in =
new FileInputStream(file1);
FileOutputStream out =
new FileOutputStream(file2);
int data;
while ((data = in.read()) >= 0)
out.write(data);
in.close(); out.close();
}
void myMain() {
try {
fileCopy (“source.txt”, “dest.txt”);
} catch (Exception e) {
e.printStackTrace();
}
}
May 21, 2004

A method can be declared to
propagate certain exceptions
to its caller by using ‘throws’

Exceptions are dynamically
bound to handlers

To insure that all exceptions
are caught, a handler can be
defined to have an
Exception class parameter

There are built-in operations
in exception objects
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
11
Exception Stack Trace in Java

Java’s exception stack trace shows the
dynamic chain of exception propagations
java.io.FileNotFoundException: source.txt (The system
cannot find the file specified)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(Unknown Source)
at java.io.FileInputStream.<init>(Unknown Source)
at ExceptionTest.fileCopy(ExceptionTest.java:9)
at ExceptionTest.myMain(ExceptionTest.java:20)
at ExceptionTest.main(ExceptionTest.java:30)
May 21, 2004
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
12
User-defined Exceptions in Java
void fileCopy(String file1, String file2)
throws MyIOException {
try {
FileInputStream in =
new FileInputStream(file1);
FileOutputStream out =
new FileOutputStream(file2);
int data;
while ((data = in.read()) >= 0)
out.write(data);
in.close(); out.close();
} catch (Exception e) {
throw new MyIOException();
}
}
May 21, 2004

User-defined exceptions
can be thrown by throw

Rethrowing (reraising)
an exception
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
13
Exception Handling in Ada (1)

Exception handlers are bound for program blocks:
begine
-- block body
exception
when exception_name { | exception_name } => statement_sequence
when ...
[when others => statement_sequence]
end;

User-defined Exceptions:
exception_name_list : exception;
raise [exception_name]

Exception conditions can be disabled with (‘pragma’ is a
directive to the compiler):
pragma SUPPRESS(exception_list)
May 21, 2004
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
14
Exception Handling in Ada (2)

Predefined Exceptions:





CONSTRAINT_ERROR - index constraints, range
constraints, etc.
NUMERIC_ERROR - numeric operation cannot
return a correct value (overflow, division by zero,
etc.)
PROGRAM_ERROR - call to a subprogram whose
body has not been elaborated
STORAGE_ERROR - system runs out of heap
TASKING_ERROR - an error associated with tasks
* AW Lecture Notes
May 21, 2004
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
15
Exception Handling in C++

Exceptions are bound to handlers through the
type of the parameter:
int new_grade;
try { if (index < 0 || index > 9)
throw (new_grade); …
} catch (int grade) {
if (grade == 100) …
}


All exceptions are user-defined
A throw without an operand can only appear in
a handler; when it appears, it simply reraises
the exception, which is then handled elsewhere
May 21, 2004
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
16
Event Handling in Java


An event is created by an external action such
as a user interaction through a GUI
The event handler is a segment of code that is
called in response to an event
A JButton
Button Pressed Event
Event Listeners
JButton helloButton = new JButton(“Hello”);
helloButton.addActionListener(new AbstractAction() {
public void actionPerformed(ActionEvent e) {
System.out.println(“Hello World!”);
}
}
May 21, 2004
ICE 1341 – Programming Languages (Lecture #21)
In-Young Ko
17