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Easy Learn Java: Programming Articles, Examples and Tips - Page 142


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Java Newsletters: Java Newsletters Archive: 11

Go to all tips in Java Newsletters

******************************************************************
* ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ *
* > The Java FAQ Daily Tips, weekly publication < *
* ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ *
* *
* Issue No: 11 15 November 2000 *
* http://www.javafaq.nu/java *
* *
* *
* Please recommend us to your friends and colleagues! *
******************************************************************

Table of Contents

>1. Is there any tool for signing and cabbing of applets? Part 1.
>2. Is there any tool for signing and cabbing of applets? Part 2.
>3. How do I make the pc speaker beep...
>4. I'd like to know which operating system java application is
running on.
>5. How can I change the default icon on application window
(java cup) to my own?
>6. Why can I put number and char together to make a comparison
without compilation error? Part 1.
>7. Why can I put number and char together to make a comparison
without compilation error? Part 2.
******************************************************************

Hello dear friends!

Java certifications are one of the most popular certifications
amongst the developer community.


Tip 1

I have made an applet in vJ++ that I have to sign. Is there any
tool to do it (both signing and cabbing)?

Answer: Signing and archive files are two of the biggest bothers in
Java. Everyone uses a different system. A good place to start is:
http://www.suitable.com/Doc_CodeSigning.shtml
One of the other bothers is that the unsigned window warning can't
be removed by signing an applet for Internet Explorer for
Macintosh. And while I am on the subject, the Windows Netscape 4.x
system has a bunch of privilege calls:
http://developer.netscape.com/docs/manuals/signedobj/capsapi.html
and you need under most circumstances to make Microsoft specific
calls too, detailed in links from:
http://www.microsoft.com/java/security/

Going through all this will make you want to curse. Unfortunately
it is hard to pick a convincing scapegoat. It is true that
Microsoft chose an entirely nonstandard CAB system, but it
produces archives that are about 40% smaller than JAR files.
Signing archive files is a perfect microcosm of the "freedom to
innovate" controversy. Microsoft has done a better job but taken
away predictability and uniformity. If the Java standards were not
controlled entirely by Sun, a Microsoft competitor, perhaps
everyone would be using smaller archive files by now.

******************************************************************

Tip 2
I have made an applet in vJ++ that I have to sign. Is there any
tool to do it (both signing and cabbing)?

answer1 in tip number 1.
Answer2: Yes. Dubuild, which you can download from the Microsoft
site as part of their Java SDK, can create signed CABs. There's
good information on the whole process at:
http://www.suitable.com/Doc_CodeSigning.shtml


******************************************************************

Tip 3
I'm doing a small console java app, and want to know what the
function is to make the pc speaker beep....

A: Toolkit.getDefaultToolkit().beep(); It is very convenient way
to alarm exeptions in program during the debugging of programs!

Tip 4
I'd like to know which operating system java application is
running on.

Answer: You could try using the system Properties.
e.g.

Properties prop = System.getProperties();

String osString = prop.getProperty( "os.name" );

******************************************************************

Tip 5
How can I change the default icon on application window (java cup)
to my own?

Answer:
window.setIconImage(Toolkit.getDefaultToolkit().getImage("image.gif"));


******************************************************************

Tip 6
Most people asked why there is an error, but my question is why
this is NOT an error. Please take a look:

r is a number and s is a character, why can I put them together
to make a comparison without compilation error?

double r = 34.5;
char s = 'c';
if (r > s) {
System.out.println("r > s");
} else {
System.out.println("r < s");
}

Answer1: char is considered to be an arithmetic type, acting as a
16 bit unsigned integer.
Conversions among the primitive types are divided into three
categories:
identity, widening, and narrowing. The identity conversions are
the trivial ones like char to char. The widening conversions all
have the effect of preserving the approximate magnitude of the
result, even if it cannot be represented exactly in the new type.
The narrowing conversions are the remaining conversions that may
destroy the magnitude information.
The compiler can insert identity and widening conversions
automatically. Narrowing conversions almost always require an
explicit cast.

char to double is one of the widening primitive conversions, so
the compiler automatically treated it as though you had written
"if ( r >(double)s)"


******************************************************************

Tip 7
Most people asked why there is an error, but my question id why
this is NOT an error.
please see first part tip number 6.

Answer2: Yes, char is indeed a 16-bit value. However, the actual
answer is in the Java Language Specification, section 5.6.2,
which is at the following URL:
http://java.sun.com/docs/books/jls/second_edition/html/conversions.doc.html#170983

In summary, the char is automagically promoted to a double. No
explicit cast is necessary since the language rules say that it
gets "promoted" to a double


The Java FAQ Daily Tips is a newsletter that is only sent to those
who have specifically subscribed to it.

John Andersson, Editor mailto:info@javafaq.nu



Copyright (c) 2000 John Andersson
******************************************************************
You can find our tips on site also!
Please recommend us to your friends and colleagues!



6 comments | Printer Friendly Page  Send to a Friend | Java Newsletters | Score: 0
Posted by jalex on Wednesday, January 28, 2004 (16:18:45) (2551 reads)

Java Newsletters: Java Newsletters Archive: 10

Go to all tips in Java Newsletters

******************************************************************
* ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ *
* > The Java FAQ Daily Tips, weekly publication < *
* ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ *
* *
* Issue No: 10 8 November 2000 *
* http://www.javafaq.nu/java *
* *
* *
* Please recommend us to your friends and colleagues! *
******************************************************************

Table of Contents

> How do I convert a binary number to an int?
> I would like to know how to test the memory, so as to avoid the
OutOfMemoryError?
> What is a Just-In-Time (JIT) compiler?
> I need to put in a JtextField characters like cyrilic ...
> How do I communicate from Java applet to JavaScript in the same
frameset?
> Is there any way to accept password from a java application?
> Is there a collection object like the hashmap or hashtable that
stores values in an ordered path? Hashmaps do not guarantee the
order of the objects...
******************************************************************

Hello dear friends!

We have two good news for you in our anniversary issue No_10 Smile!

First: We almost ready with compilation of our free for our
subscribers "100 Java Tips" e-book!
It will contain 100 Java FAQ tips from our site in comfortable for
reading and printing out form. We are planning to continue this
work and publish free to you "200 Java Tips", "300 ..." and so on.
When it will be big enough we are planning sale it, but not to you!
You will still get it for free as a subscriber of our newsletter!

And our tips here!
******************************************************************

Tip 1

I cannot find the method to convert a binary number to an int. I
used Integer.toBinaryString to get a decimal to binary but I don't
know how to to convert it back.

A: Try using Integer.parseInt (String s, int radix) with radix = 2
that should do your job


******************************************************************

Tip 2

I would like to know whether it is possible to test the memory, so
as to avoid the OutOfMemoryError or whether it is possible to
increase the amount of memory in the JRM.

Answer: You can get the total and available memory used by the VM
by making two calls from the Runtime class:

Runtime runtime = Runtime.getRuntime();
long free = runtime.freeMemory(); //the available memory
long total = runtime.totalMemory(); // the total for the JVM

The amount returned be totalMemory() isn't that useful unless you
specify how much memory your program will have from the beginning
(if you don't, the JVM will just keep grabbing more until
you run out).
You can set the initial and maximum memory from the command line:

java -Xms64m -Xmx64m name.of.Application

This will start your appplication with 64 megs initial and maximum
memory.

******************************************************************

Tip 3

What is a Just-In-Time (JIT) compiler?

Answer: It is a JVM that compiles Java instructions
(called bytecode) into native machine instructions at run time and
then uses this compiled native code when the corresponding Java
code is needed. This eliminates the constant overhead of
interpretation which tradition first generation JVM's used.


Tip 4

I need to put in a JtextField characters like cyrilic ...

How can I do this?

Answer: You use the unicode string u???? corresponding to your
character.
A table of codes can be found at www.unicode.org/charts/


******************************************************************

Tip 5

I need to communicate some data (string) from a Java Applet to
another ASP page in the same frameset. I would like to avoid a
server roundtrip and do it all with JavaScript if possible.

Therefore I would like to call some javascript from a Java Applet.
It looks like it is not possible without a netscape package. Is
that true? Is there a simple implementation of the same
functionality (source code), which I could incorporate in my applet?

Answer: Those Netscape packages are part of the current VM of
both Microsoft IE 4+ and Netscape 4+. So, by adding the MAYSCRIPT
tag to your Applet declaration, in the Java code you can obtain a
handle to the document and call functions in it.

******************************************************************

Tip 6

Is there any way to accept password from a java application? As it
is a password, IT SHOULD NOT BE SHOWN (ECHOED) WHILE IT IS ENTERED.

A: If you are using swing, you can use JPasswordField, and set your
echo character

******************************************************************

Tip 7

Is there a collection object like the hashmap or hashtable that
stores values in an ordered path? Vector does this but i need the
key/value functionality. Hashmaps do not guarantee the order of
the objects.

Answer: Take a look at java.util.TreeMap.
Red-Black tree based implementation of the SortedMap interface.
This class guarantees that the map will be in ascending key order,
sorted according to the natural order for the key's class
(see Comparable), or by the comparator provided at creation time,
depending on which constructor is used.

Note that this implementation is not synchronized. If multiple
threads access a map concurrently, and at least one of the threads
modifies the map structurally, it must be synchronized externally.


The Java FAQ Daily Tips is a newsletter that is only sent to those
who have specifically subscribed to it.

John Andersson, Editor mailto:info@javafaq.nu

Copyright (c) 2000 John Andersson
******************************************************************
You can find our tips on site also!
Please recommend us to your friends and colleagues!



45 comments | Printer Friendly Page  Send to a Friend | Java Newsletters | Score: 0
Posted by jalex on Wednesday, January 28, 2004 (16:16:18) (2715 reads)

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