What's wrong with this try/catch/finally?

5 Message(s) by 5 Author(s) originally posted in java developer

From: dba_222

Date: Thursday, August 12, 2004

Dear experts,

I'm trying to learn JAVA on my own. I picked up a
sample online, but it isn't compiling right:------------------------------------------------

import JAVA.io.*;public class

1. <programming> The prototype for an {object} in an
	{object-oriented language}; analogous to a {derived type} in a
	{procedural language}.  A class may also be considered to be a
	set of objects which share a common structure and behaviour.
	The structure of a class is determined by the {class
	variables} which represent the {state} of an object of that
	class and the behaviour is given by a set of {methods}
	associated with the class.

	Classes are related in a {class hierarchy}.  One class may be
	a specialisation (a "{subclass}") of another (one of its
	"{superclasses}") or it may be composed of other classes or it
	may use other classes in a {client-server} relationship.  A
	class may be an {abstract class} or a {concrete class}.

	See also {signature}.

	2. <programming> See {type class}.

	3. <networking> One of three types of {Internet addresses}
	distinguished by their most significant bits.

	3. <language> A language developed by the {Andrew Project}.
	It was one of the first attempts to add {object-oriented}
	features to {C}.

	(1995-05-01)

FileInfo { public static void main(String[] args) {

for (int I = 0; I < args.length; i++) {
File f = new File(args[i]);
if (f.exists()) {
System.out.println("getName: " + f.getName());
System.out.println("getPath: " + f.getPath());
System.out.println("getAbsolutePath: " + f.getAbsolutePath());
try {
System.out.println("getCanonicalPath: " + f.getCanonicalPath());
}
catch (IOException e) {
}
System.out.println("getParent: " + f.getParent());
if (f.canWrite()) System.out.println(f.getName() + " is writable.");
if (f.canRead()) System.out.println(f.getName() + " is readable.");
if (f.isFile()) {
System.out.println(f.getName() + " is a file

<file system> An element of data storage in a {file system}.

	The history of computing is rich in varied kinds of files and
	{file systems}, whether ornate (e.g., {Macintosh file system}
	for a well-known case) or deficient (e.g., many simple
	pre-1980s file systems don't allow {directories}).

	However, the prototypical file has these characteristics:

	* It is a single sequence of bytes (but consider {Macintosh}
	{resource forks}).

	* It has a finite length, unlike, e.g. a {Unix} {device}.

	* It is stored in a {non-volatile storage} medium (but see
	{ramdrive}).

	* It exists (nominally) in a {directory}.

	* It has a name that it can be referred to by in file
	operations, possibly in combination with its {path}.

	Additionally, a file system may associate other information
	with a file, such as {permission} bits or other {file
	attributes}; timestamps for file creation, last revision, and
	last access; revision numbers (a` la VMS), and other kinds of
	{magic}.

	Compare: {document}.

	(1997-04-08)

.");
}
else if (f.isDirectory()) {
System.out.println(f.getName() + " is a directory.");
}
else {
System.out.println("What is this?");
}
if (f.isAbsolute()) {
System.out.println(f.getName() + " is an absolute path.");
}
else {
System.out.println(f.getName() + " isn't an absolute path.");
}
try {
System.out.println("Last Modified" + f.lastModified());
System.out.println(f.getName() + " is " + f.length() + " bytes.");
System.out.println(f.getName() + " is " + f.length() + " bytes.");
}
catch (IOException e) {
}

}
else {
System.out.println("I'm sorry. I can not find the file " + args[i]);
}

}

} /* main */

} /* class */------------------------------------------------

JAVAc -classpath %CLASSPATH%;. FileInfo.JAVA
FileInfo.JAVA:44: exception

An error condition that changes the normal {flow of control}
	in a program.  An exception may be generated ("raised") by
	{hardware} or {software}.  Hardware exceptions include
	{reset}, {interrupt} or a signal from a {memory management
	unit}.  Exceptions may be generated by the {arithmetic logic
	unit} or {floating-point unit} for numerical errors such as
	divide by zero, {overflow} or {underflow} or {instruction
	decoding} errors such as privileged, reserved, {trap} or
	undefined instructions.  Software exceptions are even more
	varied and the term could be applied to any kind of error
	checking which alters the normal behaviour of the program.

	(1994-10-31)

JAVA.io.IOException is never thrown in body of
corresponding try statement
catch (IOException e) {
^
------------------------------------------------And yet, from what I've looked at, it looks the same as
other try/catch/finally. I've fudged it this way, to get it compile:------------------------------------------------

try {
System.out.println(args[0]);
System.out.println("Last Modified: " + f.lastModified());
System.out.println(f.getName() + " is " + f.length() + " bytes.");
} finally {
System.out.println("finally");
}

}
/*
try {
System.out.println("Last Modified" + f.lastModified());
System.out.println(f.getName() + " is " + f.length() + " bytes.");
catch (IOException e) {
}

}
*/

}
else {
System.out.println("I'm sorry. I can not find the file " + args[i]);
}

}------------------------------------------------But, how to get the original to work with /try/catch/finally? Thanks a lot!

From: Thomas Schodt

Date: Thursday, August 12, 2004

wrote in message

In {object-oriented programming} sending a message to an
	{object} (to invoke a {method}) is equivalent to calling a
	{procedure} in traditional programming languages, except that
	the actual code executed may only be selected at run time
	depending on the {class} of the object.  Thus, in response to
	the message "drawSelf", the method code invoked would be
	different if the target object were a circle or a square.

	(1995-02-16)

try {
System.out.println("Last Modified" + f.lastModified());
System.out.println(f.getName() + " is " + f.length() + " bytes.");
System.out.println(f.getName() + " is " + f.length() + " bytes.");
}
catch (IOException e) {
}To be able to catch a checked exception

a method

<programming> The name given in {Smalltalk} and other
	{object-oriented languages} to a procedure or routine
	associated with one or more {classes}.  An {object} of a
	certain class knows how to perform actions, e.g. printing
	itself or creating a new instance of itself, rather than the
	function (e.g. printing) knowing how to handle different types
	of object.

	Different classes may define methods with the same name
	(i.e. methods may be {polymorphic}).  The term "method" is used
	both for a named operation, e.g. "PRINT" and also for the code
	which a specific class provides to perform tha
	t operation.

	Most methods operate on objects that are instances of a
	certain class.  Some object-oriented languages call these
	"object methods" to distinguish then from "{class methods}".

	In {Smalltalk}, a method is defined by giving its name,
	documentation, temporary local variables and a sequence of
	expressions separated by "."s.

	(2000-03-22)

inside the try block

1. <unit> A unit of data or memory, often, but not
	exclusively, on a {magnetic disk} or {magnetic tape}.

	Compare {record}, {sector}.

	(2000-07-17)

	2. <operating system> To delay or sit idle while waiting for
	something.

	Compare {busy-wait}.

	(2000-07-17)

	3. <programming> A delimited section of {source code} in a
	{block-structured} language.

	(2004-09-29)

must declare that it throws that exception
(or one derived from it).

File.lastModified() isn't declared to throw any exceptions.

You can completely omit the try/catch block around those three lines
or you can replace that empty catch block with an empty finally block.

Note: Empty (and uncommented) catch blocks are commonly frowned upon.

From: brandon

Date: Thursday, August 12, 2004

wrote in message:

Dear experts,
I'm trying to learn JAVA on my own. I picked up a
sample online, but it isn't compiling right:
------------------------------------------------
import JAVA.io.*;
public class FileInfo {
public static void main(String[] args) {
for (int I = 0; I < args.length; i++) {
File f = new File(args[i]);
if (f.exists()) {
System.out.println("getName: " + f.getName());
System.out.println("getPath: " + f.getPath());
System.out.println("getAbsolutePath: " + f.getAbsolutePath());
try {
System.out.println("getCanonicalPath: " + f.getCanonicalPath());
}
catch (IOException e) {
}
System.out.println("getParent: " + f.getParent());
if (f.canWrite()) System.out.println(f.getName() + " is writable.");
if (f.canRead()) System.out.println(f.getName() + " is readable.");
if (f.isFile()) {
System.out.println(f.getName() + " is a file.");
}
else if (f.isDirectory()) {
System.out.println(f.getName() + " is a directory.");
}
else {
System.out.println("What is this?");
}
if (f.isAbsolute()) {
System.out.println(f.getName() + " is an absolute path.");
}
else {
System.out.println(f.getName() + " isn't an absolute path.");
}
try {
System.out.println("Last Modified" + f.lastModified());
System.out.println(f.getName() + " is " + f.length() + " bytes.");
System.out.println(f.getName() + " is " + f.length() + " bytes.");
}
catch (IOException e) {
}
}
else {
System.out.println("I'm sorry. I can not find the file " + args[i]);
}
}
} /* main */
} /* class */
------------------------------------------------
JAVAc -classpath %CLASSPATH%;. FileInfo.JAVA
FileInfo.JAVA:44: exception JAVA.io.IOException is never thrown in body of
corresponding try statement
catch (IOException e) {
^
------------------------------------------------
And yet, from what I've looked at, it looks the same as
other try/catch/finally.
I've fudged it this way, to get it compile:
------------------------------------------------
try {
System.out.println(args[0]);
System.out.println("Last Modified: " + f.lastModified());
System.out.println(f.getName() + " is " + f.length() + " bytes.");
}
finally {
System.out.println("finally");
}
}
/*
try {
System.out.println("Last Modified" + f.lastModified());
System.out.println(f.getName() + " is " + f.length() + " bytes.");
catch (IOException e) {
}
}
*/
}
else {
System.out.println("I'm sorry. I can not find the file " + args[i]);
}
}
------------------------------------------------
But, how to get the original to work with /try/catch/finally?
Thanks a lot!The problem is in this part of the code
<software> Instructions for a computer in some programming
	language, often {machine language}.  The word "code" is often
	used to distinguish instructions from {data} (e.g. "The code
	is marked 'read-only'") whereas "{software}" is used in
	contrast with "{hardware}" and may consist of more than just
	code.

	(2000-04-08)
:

---

try {
System.out.println("Last Modified" + f.lastModified());
System.out.println(f.getName() + " is " + f.length() + " bytes.");
System.out.println(f.getName() + " is " + f.length() + " bytes.");
}
catch (IOException e) {
}

---

In this particular try-block, there are no methods which are capable
of throwing an IOException, so this IOexception cannot be 'catched'
in this case.

You can make this example working by removing the try-catch block,
like this :

---

System.out.println("Last Modified" + f.lastModified());
System.out.println(f.getName() + " is " + f.length() + " bytes.");
System.out.println(f.getName() + " is " + f.length() + " bytes.");

---

From: Bryce

Date: Thursday, August 12, 2004

On 12 Aug 2004 06:02:59 -0700, dba_222@xxxxxxxxxxx (Roger Redford)
wrote in message:

Java

<programming, language, portability> (After the Indonesian island, a
	source of {programming fluid}) A simple, {object-oriented},
	{distributed}, {interpreted}, robust, secure,
	{architecture-neutral}, {portable}, {multithreaded}, dynamic,
	buzzword-compliant, general-purpose programming language
	developed by {Sun Microsystems} in the early 1990's (initially for
	set-top television controllers), and released to the public in 1995.

	Java first became popular by being the earliest portable
	dynamic client-side content for the {World-Wide Web} in the
	form of {platform}-independent Java "applets". In the late
	1990's and into the 2000's it has also become very popular
	on the server side, where an entire set of {APIs} defines the {J2EE}.

	Java is both a set of public specifications (controlled by
	{Sun Microsystems} through the {JCP}) and a series of
	implementations of those specifications.

	Java is syntactially similar to {C++} without user-definable
	{operator overloading}, (though it does have {method}
	overloading), without {multiple inheritance}, and extensive
	automatic {coercions}.  It has automatic {garbage collection}.
	Java extends {C++}'s {object-oriented} facilities with those
	of {Objective C} for {dynamic method resolution}.

	Whereas programs in C++ and similar languages are compiled
	and linked to platform-specific binary executables, Java
	programs are typically compiled to portable {architecture-neutral}
	{bytecode} or ".class" files, which are run using a {Java
	Virtual Machine}.  The JVM is also called an {interpreter},
	though it is more correct to say that it uses {Just-In-Time
	Compilation} to convert the {bytecode} into {native} {machine
	code}, yielding greater efficiency than most interpreted
	languages, rivalling C++ for many long-running, non-GUI
	applications.  The run-time system is typically written in
	{POSIX}-compliant {ANSI C} or {C++}.  Some implementations
	allow Java class files to be translated into {native}
	{machine code} during or after compilation.

	The Java compiler and {linker} both enforce {strong type
	checking} - procedures must be explicitly typed.  Java
	supports the creation of {virus}-free, tamper-free systems
	with {authentication} based on {public-key encryption}.

	Java has an extensive library of routines for all kinds of
	programming tasks, rivalling that of other languages.

	For example, the "java.net} package supports {TCP/IP}
	{protocols} like {HTTP} and {FTP}.  Java applications can
	access objects across the {Internet} via {URLs} almost as easily as
	on the local {file system}. There are also capabilities for
	several types of distributed applications.

	The Java {GUI} libraries provide portable interfaces.  For example,
	there is an abstract Window class and implementations of it
	for {Unix}, {Microsoft Windows} and the {Macintosh}.
	The "java.awt" and "javax.swing" classes can be used either in
	Web-based "Applets" or in client-side or "desktop" applications.

	There are also packages for developing {XML} applications,
	{web services}, {servlets} and other web applications,
	{security}, date and time calculations and I/O formatting,
	database ({JDBC}), and many others.

	Java is not directly related to {JavaScript} despite the name.

	{Home (http://java.sun.com/)}.

	{Usenet} newsgroup: {news:comp.lang.java}.

	(2005-01-21)

c -classpath %CLASSPATH%;. FileInfo.JAVA
FileInfo.JAVA:44: exception JAVA.io.IOException is never thrown in body of
corresponding try statement
catch (IOException e) {
^

The error

1. A discrepancy between a computed, observed, or measured
	value or condition and the true, specified, or theoretically
	correct value or condition.

	2. <programming> A mental mistake made by a programmer that
	may result in a program {fault}.

	3. (verb) What a program does when it stops as result of a
	programming error.

	(2000-03-28)

tells you what you need to know. Nothing in the surrounding
try block throws an IOException.

--
now with more cowbell

From: Thomas G. Marshall

Date: Saturday, August 14, 2004

Roger Redford <dba_222@xxxxxxxxxxx> coughed up the following:

Dear experts,
I'm trying to learn JAVA on my own. I picked up a
sample online, but it isn't compiling right:The others here have given you insight as to the problem, but FWIW
For what it's worth.
I'd like
to add something.

When you move up to the jdk1.5 release, there is a -Xlint option

<software> (Or "option", "flag", "switch", "option switch") An
	argument to a command that modifies its function rather than
	providing data.  Options generally start with "-" in {Unix} or
	"/" in {MS-DOS}.  This is usually followed by a single letter
	or occasionally a digit.

	Some commands require each option to be a separate argument,
	introduced by a new "-" or "/", others allow multiple option
	letters to be concatenated into a single argument with a
	single "-" or "/", e.g. "ls -al".  A few Unix commands
	(e.g. {ar}, {tar}) allow the "-" to be omitted.  Some options
	may or must be followed by a value, e.g. "cc prog.c -o prog",
	sometimes with and sometimes without an intervening space.

	{getopt} and {getopts} are commands for parsing command line
	options.  There is also a {C} library routine called getopt
	for the same purpose.

	(1996-12-11)

that will
give you every single warning possible for your code. While you certainly
had enough of an error message from your compiler

<programming, tool> A program that converts another program
	from some {source language} (or {programming language}) to
	{machine language} (object code).  Some compilers output
	{assembly language} which is then converted to {machine
	language} by a separate {assembler}.

	A compiler is distinguished from an assembler by the fact that
	each input statement does not, in general, correspond to a
	single machine instruction or fixed sequence of instructions.
	A compiler may support such features as automatic allocation
	of variables, arbitrary arithmetic expressions, control
	structures such as FOR and WHILE loops, variable {scope},
	input/ouput operations, {higher-order functions} and
	{portability} of source code.

	{AUTOCODER}, written in 1952, was possibly the first primitive
	compiler.  {Laning and Zierler}'s compiler, written in
	1953-1954, was possibly the first true working algebraic
	compiler.

	See also {byte-code compiler}, {native compiler}, {optimising
	compiler}.

	(1994-11-07)

in this particular case,
when you move to 1.5 the Xlint warnings will help you understand fundamental
mistakes based upon assumptions. In theory.

BTW, comp.lang.JAVA is a "retired" newsgroup, and I do not ever remember
comp.lang.JAVA.developer ever being valid. Even though you can access the
unofficial ones, the official ones are:

comp.lang.JAVA.3d 3D Graphics API's for the JAVA language.
comp.lang.JAVA.advocacy Support for and criticism of the JAVA System.
comp.lang.JAVA.announce Announcements re the JAVA System. (Moderated)
comp.lang.JAVA.beans JAVA software

<programming> (Or "computer program", "program", "code") The
	instructions executed by a computer, as opposed to the
	physical device on which they run (the "{hardware}").

	The term was coined by the eminent statistician, {John Tukey}.

	Programs stored on {non-volatile storage} built from
	{integrated circuits} (e.g. {ROM} or {PROM}) are usually
	called {firmware}.

	Software can be split into two main types - {system software}
	and application software or {application programs}.  System
	software is any software required to support the production or
	execution of application programs but which is not specific to
	any particular application.  Examples of system software would
	include the {operating system}, {compilers}, editors and
	sorting programs.

	Examples of application programs would include an accounts
	package or a {CAD} program.  Other broad classes of
	application software include {real-time} software, {business
	software}, scientific and engineering software, {embedded
	software}, personal computer software and {artificial
	intelligence} software.

	Software includes both {source code} written by humans and
	executable {machine code} produced by {assemblers} or
	{compilers}.  It does not usually include the data processed
	by programs unless this is in a format such as {multimedia}
	which depends on the use of computers for its presentation.
	This distinction becomes unclear in cases such as {spread
	sheets} which can contain both instructions (formulae and
	{macros}) and data.  There are also various intermediate
	compiled or {semi-compiled}, forms of software such as
	{library} files and {byte-code}.

	Some claim that {documentation} (both paper and electronic) is
	also software.  Others go further and define software to be
	programs plus documentation though this does not correspond
	with common usage.

	The noun "program" describes a single, complete and
	more-or-less self-contained list of instructions, often stored
	in a single {file}, whereas "code" and "software" are
	uncountable nouns describing some number of instructions which
	may constitute one or more programs or part thereof.  Most
	programs, however, rely heavily on various kinds of {operating
	system} software for their execution.  The nounds "code" and
	"software" both refer to the same thing but "code" tends to
	suggest an interest in the implementation details whereas
	"software" is more of a user's term.

	(2002-07-21)

components (JAVABeans).
comp.lang.JAVA.corba Topics relating to JAVA and CORBA.
comp.lang.JAVA.databases Databases, JAVA.sql, JDBC, ODBC.
comp.lang.JAVA.gui GUI

<operating system> (GUI) The use of pictures rather than just
	words to represent the input and output of a program.  A
	program with a GUI runs under some {windowing system}
	(e.g. The {X Window System}, {MacOS}, {Microsoft Windows},
	{Acorn} {RISC OS}, {NEXTSTEP}).  The program displays certain
	{icons}, {buttons}, {dialogue boxes}, etc. in its {windows} on
	the screen and the user controls it mainly by moving a
	{pointer} on the screen (typically controlled by a {mouse})
	and selecting certain objects by pressing buttons on the mouse
	while the pointer is pointing at them.  This contrasts with a
	{command line interface} where communication is by exchange of
	strings of text.

	Windowing systems started with the first {real}-time graphic
	display systems for computers, namely the {SAGE} Project
	[Dates?] and {Ivan Sutherland}'s {Sketchpad} (1963).  {Douglas
	Engelbart}'s {Augmentation of Human Intellect} project at
	{SRI} in the 1960s developed the {On-Line System}, which
	incorporated a mouse-driven cursor and multiple windows.
	Several people from Engelbart's project went to Xerox PARC in
	the early 1970s, most importantly his senior engineer, {Bill
	English}.  The Xerox PARC team established the {WIMP} concept,
	which appeared commercially in the {Xerox 8010} (Star) system
	in 1981.

	Beginning in 1980(?), led by {Jef Raskin}, the {Macintosh}
	team at {Apple Computer} (which included former members of the
	Xerox PARC group) continued to develop such ideas in the first
	commercially successful product to use a GUI, the Apple
	Macintosh, released in January 1984.  In 2001 Apple introduced
	{Mac OS X}.

	{Microsoft} modeled the first version of {Windows}, released
	in 1985, on Mac OS.  Windows was a GUI for {MS-DOS} that had
	been shipped with {IBM PC} and compatible computers since
	1981.  Apple sued Microsoft over infringement of the
	look-and-feel of the MacOS.  The court case ran for many
	years.

	[Wikipedia].

	(2002-03-25)

toolkits and windowing: AWT, IFC

<language, library, programming, standard> (IFC) A {library}
	of {classes} used in the creation of {Java} {applets} with
	{GUIs}.

	Created by {Netscape}, the Internet Foundation Classes provide
	GUI elements, as well as classes for {Applications Services},
	{Security}, {Messaging}, and {Distributed Objects}.

	The IFC code, which is exclusively Java, is layered on top of
	the Java {Abstract Windowing Toolkit} (AWT), thus preserving
	{platform independence}.

	The AWT and IFC collectively form the {Java Foundation
	Classes}, which provide a standardised framework for
	developing powerful Java applications.

	{IFC download (http://wp.netscape.com/eng/ifc/download.html)}.

	(2003-08-17)

etc.
comp.lang.JAVA.help Set-up problems, catch-all first aid.
comp.lang.JAVA.machine JVM, native methods, hardware.
comp.lang.JAVA.programmer Programming in the JAVA language.
comp.lang.JAVA.security Security issues raised by JAVA.
comp.lang.JAVA.softwaretools IDEs, browsers, compilers, other tools.

Try to stay within that list.

...[stomp]...

--
http://www.allexperts.com is a nifty way to get an answer to just about
/anything/.

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