To Be Creative

Servlets and thread safty

2012-01-31T01:02:00.001+02:00

From Servlet 2.4 specs:

SRV.2.3.3.3
Thread Safety
Implementations of the request and response objects are not guaranteed to be thread
safe. This means that they should only be used within the scope of the request han-
dling thread.
References to the request and response objects should not be given to objects
executing in other threads as the resulting behavior may be nondeterministic. If
the thread created by the application uses the container-managed objects, such as
the request or response object, those objects must be accessed only within the
servlet’s service life cycle and such thread itself should have a life cycle within
the life cycle of the servlet’s service method because accessing those objects
after the service method ends may cause undeterministic problems. Be aware
that the request and response objects are not thread safe. If those objects were
accessed in the multiple threads, the access should be synchronized or be done
through the wrapper to add the thread safety, for instance, synchronizing the call
of the methods to access the request attribute, or using a local output stream for
the response object within a thread.

When the destroy method gets called in the Servlet?

2012-01-31T00:59:00.002+02:00

It is an implementation-depended, nobody knows!

SRV.2.3.4
End of Service
The servlet container is not required to keep a servlet loaded for any particular
period of time. A servlet instance may be kept active in a servlet container for a
period of milliseconds, for the lifetime of the servlet container (which could be a
number of days, months, or years), or any amount of time in between.
When the servlet container determines that a servlet should be removed from
service, it calls the destroy method of the Servlet interface to allow the servlet to
release any resources it is using and save any persistent state. For example, the
container may do this when it wants to conserve memory resources, or when it is
being shut down.
Before the servlet container calls the destroy method, it must allow any
threads that are currently running in the service method of the servlet to complete
execution, or exceed a server-defined time limit.
Once the destroy method is called on a servlet instance, the container may
not route other requests to that instance of the servlet. If the container needs to
enable the servlet again, it must do so with a new instance of the servlet’s class.
After the destroy method completes, the servlet container must release the
servlet instance so that it is eligible for garbage collection.

Source Servelt-2.4 specs document

How easy to parse JSON in JS

2012-01-31T00:41:00.000+02:00

It is that easy!

var myObj = eval("obj={'name':'ali', 'age':'20'}");

document.write (myObj.name + ' ' + myObj.age);

Always encode the return URL

2012-01-30T23:06:00.002+02:00

Sometimes, we need to put some url as a parameter in the page url, example:

https://open.login.yahoo.com/openid/yrp/signin?returnUrl=http%3A%2F%2Fmail.yahoo.com&rpcrumb=TzwDznuzRzH&.src=ym

The value of parameter "returnUrl" is an encoded url (http%3A%2F%2Fmail.yahoo.com)

So, whenever you want to put a URL as a parameter, you have to URL encode it.

(you can use JS function encodeUrlComponenet

Paging in Oracle

2012-01-30T14:39:00.001+02:00

To do paging in oracle, the best way is to use:


SELECT * FROM
(
    SELECT a.*, rownum r__
    FROM
    (
        SELECT * FROM ORDERS WHERE CustomerID LIKE 'A%'
        ORDER BY OrderDate DESC, ShippingDate DESC
    ) a
    WHERE rownum < ((pageNumber * pageSize) + 1 )
)
WHERE r__ >= (((pageNumber-1) * pageSize) + 1)

Source: http://stackoverflow.com/questions/241622/paging-with-oracle#241643

First-class Functions

2012-01-23T09:20:00.000+02:00

In computer science, a programming language is said to have first-class functions if it treats functions as first-class objects. Specifically, this means that the language supports passing functions as arguments to other functions, returning them as the values from other functions, and assigning them to variables or storing them in data structures.

SMAuth, Simple Mobile Authentication

2012-01-21T17:05:00.001+02:00

SMAuth is a simple mobile (and desktop) apps authentication schema. SMAuth is most suitable to run over HTTPS.

The whole idea here is to keep the client out of persisting the username/password and instead persist a token that will expire.

SMAuth is more suitable for Mobile and Desktop applications where the Resource owner (who know the username/password) is the client himself.

Learn More: http://code.google.com/p/smauth/

code: https://smauth.googlecode.com/svn/trunk/

The names of the primary key fields must correspond

2012-01-16T21:51:00.000+02:00

I've faced some JPA Error (deployment-time error) which is:

The names of the primary key fields or properties in the primary key class [class FooBarPK] and those of the entity bean class [class FooBar] must correspond and their types must be the same. Also, ensure that you have specified id elements for the corresponding attributes in XML and/or an @Id on the corresponding fields or properties of the entity class.

The error appears when deploying some JPA project in Oracle App Server.

I've this entity:

@Entity
@IdClass(FooBarPK.class)
public class FooBar implements Serializable {
    
    private static final long serialVersionUID = 1L;
    

    @Id
    private Long id1;
    @Id
    private Long id2;
    
    //...
}

//And this is the PK class 

public class NewParaPK implements Serializable 
{
    private static final long serialVersionUID = 1L;

    private Long id1;
    private Long id2;
}

I wonder, why this happen...

I found this line:

private static final long serialVersionUID = 1L;

In the PK Class who cases the problem!

Returning array from function in C

2012-01-15T01:19:00.001+02:00

I've here very intersting discussion about the best and common ways to return an array from a function..

Some solutions to use output parameter and copy the value of the array into the value of this output parameter array.
Other solution to pass an array and use it inside the function.

Others to allocate the array inside the function and return refrence to it, but the caller have to free it once done.

Others to return a struct contains this pointer...

Please enjoy; stackoverflow.com/questions/8865982/return-array-from-function-in-c

Get base, simple, non-acurate function

2012-01-15T00:39:00.000+02:00

I've wrote a function to get a number string in some arbitrary bases.

I claim that this function is not accurate.

Here's the source code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void getBase(int num, int base, char* string);
char numbers[] = {'0', '1', '2', '3',
                  '4', '5', '6', '7',
                  '8', '9', 'A', 'B',
                  'C', 'D', 'E', 'F'};

int
main (int argc, char *argv[])
{
    char str[32];

    getBase(2, 2, str);
    printf("%s\n", str);

    getBase(255, 16, str);
    printf("%s\n", str);


    getBase(769878, 10, str);
    printf("%s\n", str);


    return 0;
}

void getBase(int n, int b, char* str)
{
    const size_t SIZE = 32;
    char arr[32+1]={0}; int digits=SIZE, i;
    char* ptr = arr;
    while (n > 0)
    {
        int t = n%b;
        n/=b;
        arr[--digits] = numbers[t];
    }
    while ( *ptr == '\0') ptr++;

    strcpy(str, ptr);
}

Oracle Encoding functions

2012-01-10T16:21:00.000+02:00

Salam,

Actually I am not interested in Oracle DB programming, but I use it some times so, I'll list here two handy functions that I use.

To get character ASCII code, use:

select ascii('a') from dual

To get the character from a code page (according to DB local encoding), use:

select chr(176) from dual

create constant object in Java

2012-01-01T16:28:00.001+02:00

I've wondered if I can create a constant object in Java? I don't mean a constant reference (which achieved by final keyword) or a class whose all of its instances are constants (a.k.a immutable objects).

I've asked a question in SO and got a staisified answers ..
Please have a look

Zipping in Java

2011-12-25T14:51:00.003+02:00

import java.io.ByteArrayOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;

public class Zipper
{

    public static byte[] zip(String[] names, byte[][] data) throws IOException
    {
        if (names == null || data == null || names.length == 0 || names.length < data.length)
     throw new IllegalArgumentException("Arguemnts are null or empty or names less than data");

        ByteArrayOutputStream outZipStream = new ByteArrayOutputStream();
        ZipOutputStream out = new ZipOutputStream(outZipStream);

        int l = data.length;
        for (int i=0; i < l; i++)
        {
            out.putNextEntry(new ZipEntry(names[i]));
            out.write(data[i]);
            out.closeEntry();
        }

        out.close();

        return outZipStream.toByteArray();
    }


    public static void main(String[] args) throws IOException
    {
        byte[] file1Data = "File 1 content".getBytes("UTF-8");
        byte[] file2Data = "File 2 content".getBytes("UTF-8");

        byte[] zippedData = zip (new String[] {"file1.txt", "file2.txt"}, new byte[][] {file1Data, file2Data});

        FileOutputStream fileOutputStream = new FileOutputStream("test.zip");
        fileOutputStream.write(zippedData);
        fileOutputStream.close();
    }
}

tagEditor, sample program utilize TagLib

2011-12-20T09:16:00.001+02:00

In a recent post, I'v talked about TagLib.

And Now here's a full functional program:

TagLib, an awesome library to edit ID3 metadata

2011-12-19T22:01:00.000+02:00

Recently, I have some MP3 files that contains its ID3 data in Arabic (I think either WINDOWS-1256 or ISO-8859-6 formats), the formats that cannot be read by Rhythmbox.

So, I have either edit in source of Rhythmbox (which is a better solution), or find a library to enable me to re-write these metadata.

I went with solution #2, I have do some search and found TagLib, a very awesome KDE library that makes this task very easy. Building the library was a straightforward task, I can say it is the first lib that I can build from source in my life .) .

Example: To compile and run:

$cc -o taglibClient taglibClient.cc -ltag
$./taglibClient
Fairouz

Type range in c++ by example

2011-11-03T20:40:00.001+02:00

Output:
Wrong Value -1
Correct Value 2147483647

The easier way to create Tabbed Bar in iPhone

2011-10-08T15:20:00.000+02:00

I see the easier way to create a UITabBar in iPhone, is through the Controller.

Only create the View yourself, if you want to customize it, otherwise, don't go that way!

Suppose we have a button that we click to open a TabBar with two UITabBarItems, as usual , we push the next controller to the UINavigationConroller ... but this time we will push a UITabBarController..

Here's the code with inline comments:

References:
http://developer.apple.com/library/ios/#DOCUMENTATION/UIKit/Reference/UITabBarController_Class/Reference/Reference.html#//apple_ref/occ/cl/UITabBarController

ObjectMapper an Objective-c lib to map data structure into user-objects

2011-10-07T11:03:00.000+02:00

I was working on iPhone project and I needed to consume data from some JSON service.

I've tried to find some library to convert returned JSON String into my own custom objects... but I didn't.

Most popular JSON libraries (JSONKit, SBJson, etc ..) just convert JSON String into Objective-c data structures (NSDictionary, NSArray). So I decided to write a lib to convert from NSDictionary and NSAarry into my own custom-objects.

ObjectMapper [https://github.com/MuhammadHewedy/ObjectMapper] is a project used to convert NSDictaionry to Custom user objects. It can used with JSON parsing libraries (JSONKit, SBJSON, etc) to convert the returned NSDictionary and NSArray into custom user objects

Example usage:

Complete Example project found here : https://github.com/MuhammadHewedy/ObjectMapper/tree/master/ObjectMapperTester
Good luck!

Centralize your NSURLConnection code while using Async connections

2011-10-01T21:59:00.000+02:00

We should use Aysnc calls when dealing with NSURLConnections. May articles illustrate why we should do that, among them is this one The truth about synchronous NSURLConnection. Also see my question on SO. But We want also to have our "Communicate" code grouped somewhere not to be implemented by all of our classes in the project. This post is talking about how to solve this issue.. Thanks to AliSoftware . Well, We will have some Utility class the doing the connection and handle the data for us.. but what will we do when we got the data from the server? we should call some method on the caller class (in cases, it is a ViewContoller).. so we should send the target class and the selector to be called when the connection done receiving data. So, Here's the code (quick and dirty) for the URLCaller class:

  1. 
  2. #import <Foundation/Foundation.h>
  3. 
  4. @interface URLCaller : NSObject
  5. {
  6.     NSMutableData* data;
  7.     NSObject* target;
  8.     SEL selector;
  9. }
 10. @property (nonatomic, retain) NSMutableData* data;
 11. @property (nonatomic, retain) NSObject* target;
 12. @property (nonatomic) SEL selector;
 13. 
 14. -(id) initWithTarget:(NSObject*) target selector:(SEL)selector;
 15. -(void) call:(NSString*) url;
 16. 
 17. @end
 18. 
 19. 
 20. #import "URLCaller.h"
 21. 
 22. @implementation URLCaller
 23. @synthesize data, target, selector;
 24. 
 25. -(id) initWithTarget:(NSObject*) _target selector:(SEL)_selector
 26. {
 27.     if (self = [super init])
 28.     {
 29.         self.target = _target;
 30.         self.selector = _selector;
 31.     }
 32.     return self;
 33. }
 34. 
 35. -(void) call:(NSString*) url
 36. {
 37.     NSURLConnection* connection = [[NSURLConnection alloc]initWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:url]] delegate:self];
 38.     [connection release];
 39. }
 40. 
 41. #pragma mark - NSURLConnection deleages
 42. 
 43. -(void)connection:(NSURLConnection*)connection didReceiveResponse:(NSURLResponse*)response
 44. {
 45.     data = [[NSMutableData alloc] init]; // _data being an ivar
 46. }
 47. -(void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)_data
 48. {
 49.     [self.data appendData:_data];
 50. }
 51. -(void)connection:(NSURLConnection*)connection didFailWithError:(NSError*)error
 52. {
 53.     // Handle the error properly
 54. }
 55. -(void)connectionDidFinishLoading:(NSURLConnection*)connection
 56. {
 57.     NSString* stringData = [[[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding]autorelease];
 58.     [target performSelector:selector withObject:stringData];
 59. }
 60. 
 61. - (void)dealloc 
 62. {
 63.     [target release];
 64.     [data release];
 65.     [super dealloc];
 66. }
 67. 
 68. @end

And in the caller class (in my case is a ViewController), we will use the URLCaller class:

  1. 
  2. -(IBAction)getDataFromServer:(id)sender
  3. {
  4.     URLCaller* caller = [[URLCaller alloc]initWithTarget:self selector:@selector(setTextViewContents:)];
  5.     [caller call:@"http://search.twitter.com/search.json?q=Muhammad"];
  6.     [caller release];
  7. }
  8. 
  9. // this will got called when the data returned from the server
 10. -(void) setTextViewContents:(NSString*) contents
 11. {
 12.     text.text = contents;
 13. }

You can get the project source code from here Very important notice is that, the application will never got freeze while the data is being transferred, and this is what we wants!

Building and installing NSJSONSerialization on gnustep to parse JSON data

2011-09-18T00:30:00.000+02:00

I was seeking for a JSON Parser for Objective-c on gnustep runtime..
Thanks to sudo rm -rf he directed me to use the source code from gnustep repository .

I got the source code for Three Files NSJSONSerialization.h, NSJSONSerialization.m and GSFastEnumeration.h, although not worked directly, I've did very small modifications

Steps to use:

Note: Steps below are executed on Mingw and should be used with little or no modifications on Linux.

Go and download the archive that contains the modified Three files from here.
put them into a directory say in your home folder with the following path: ~/objc/json
cd ~/objc/json and issue the following command to build the files:
gcc -c `gnustep-config --objc-flags` *.m
If no errors reported, this means the build process succeed. and the object file has been generated.
Now let's put this files inside the gnustep installation, to do so, mv the the .h files NSJSONSerialization.h and GSFastEnumeration.h to /GNUstep/System/Library/Headers/Foundation
Now let's create a static library and put it inside gnustep libraries path:
Use the following command:
ar q libNSJSONSerialization.a NSJSONSerialization.o Then move the generated libNSJSONSerialization.a file to /GNUstep/System/Library/Libraries/

Note that, we now copied two .h files and one .a file into gnustep installation directories.
You now safe to remove all the directory ~/objc/json and all of its contents.

Now You are done installing the NSJSONSerialization as a static lib into gnustep.

Now let's write a test program. Now create a brand new directory into your home directory say ~/objc/json_test and create a file named json_main.m in this directory.
Put the following code in it:

  1. #import <Foundation/Foundation.h>
  2. #import <Foundation/NSJSONSerialization.h>
  3. 
  4. int main(void)
  5. {
  6.     NSAutoreleasePool* pool = [[NSAutoreleasePool alloc]init];
  7. 
  8.     NSDictionary* dictionary = [NSDictionary dictionaryWithObjects:
  9.                 [NSArray arrayWithObjects: @"Muhammad", @"26", @"2011", @"Cairo, Egypt", 
 10.                 [NSArray arrayWithObjects: @"Arabic", @"English", nil] , nil]
 11.                                                             forKeys: 
 12.                 [NSArray arrayWithObjects: @"name", @"age", @"year", @"address", @"language", nil]];
 13.     NSError* error;
 14.     NSData* data = [NSJSONSerialization dataWithJSONObject: dictionary
 15.                 options:NSJSONWritingPrettyPrinted
 16.                 error: &error];
 17.     if (error)
 18.     {
 19.         NSLog(@"ERROR %@", error);
 20.     }else
 21.     {
 22.         NSString* jsonString = [[NSString alloc] initWithData: data 
 23.                                         encoding: NSASCIIStringEncoding];
 24.         NSLog(@"%@", jsonString);
 25.                     
 26.         [jsonString release];        
 27.     }
 28. 
 29.     [pool release];
 30.     return 0;
 31. }

Now use the following command to compile it:


 gcc `gnustep-config --objc-flags` *.m  -L /GNUstep/System/Library/Libraries -lNSJSONSerialization -lobjc -lgnustep-base

[The inclusion for the libraries should be exactly in this order]

Now run:


$ a.exe

2011-09-18 01:35:49.726 a[5696] {

"language": [

        "Arabic",

        "English"

        ],

"year": "2011",

"name": "Muhammad",

"age": "26",

"address": "Cairo, Egypt"

}

Congratulations! you can use gnustep to parse json data.

Disclaimer: This article is distributed in the hope that it will be useful, but without any warranty. Use it on your own.

NSData wraps array of bytes (8bits) so beware when use it

2011-09-13T23:57:00.000+02:00

SA, Objc NSData object wraps array of bytes so you should send the size parameter properly.. suppose you want to wrap an array of a custom struct Emp.. you have to specify the size of the Array as number of bytes as following: sizeof(StructType)* array_length See the following example carefully:

  1. #import <Foundation/Foundation.h>
  2. 
  3. int main(void)
  4. {
  5. 
  6.     NSAutoreleasePool* pool = [NSAutoreleasePool new];
  7. 
  8.     typedef struct
  9.     {
 10.         char* name;
 11.         int   hiredate;
 12.     }Emp;
 13.     
 14.     Emp emps[] = {{"Mouhammad", 2010}, {"Moutaz", 2010}, {"Ahmad", 2010}};
 15.     
 16.     NSData* data = [NSData dataWithBytes : emps length: sizeof(Emp) * 3 ];    // here we specify the number of BYTES to be holded
 17.     
 18.     Emp* newEmps = [data bytes];
 19.     int count = [data length]/ sizeof(Emp);            // here we go the number of bytes holded, 
 20.                                             //watch the division of the total number of bytes
 21.                                             // over the size of each struct element
 22.     
 23.     int i=0;
 24.     for (; i< count; i++)
 25.     {
 26.         Emp e = *newEmps;
 27.         NSLog(@"%s %i", e.name, e.hiredate);
 28.         newEmps++;
 29.     }
 30.     
 31. 
 32.     [pool release];
 33.     return 0;
 34. }

The power of Objective-c categories.. add category for NSData object

2011-09-12T23:47:00.003+02:00

Categories is a very powerful feature in objective-c.. we will show how to use it to overrides the function "description" of the NSData object in the following example:

#import <Foundation/Foundation.h>
#import "../../mem.h"

@interface NSDate(description)
-(NSString*) description;
@end

@implementation NSData(description)
-(NSString*) description
{
    int len = [self length];
    char buff[len];
    [self getBytes: buff];
    
    NSMutableString* ret = [NSMutableString string];
    
    int i;
    for (i=0; i < len; i++)
        [ret appendFormat: @"%i ", buff[i] ];
    
    return ret;
}
@end

int main(void)
{
    POOL;
    char arr[]= {10, 20, 30};
    
    NSData* data = [NSData dataWithBytes:arr length: sizeof(arr)/sizeof(char)];
    
    NSLog(@"%@", [data description]);

    _POOL;
    return 0;
}

Note, POOL and _POOL are two macros defined in "../../mem.h" as follow: #define POOL NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init] #define _POOL [pool drain]

How to determine the amount of memory required by my char* in struct?

2011-09-12T11:20:00.001+02:00

Suppose you have the following C struct:

  1. typedef struct
  2. {
  3.     char* name;
  4. }Emp;

I asked in SO on how to determine the amount of memory to allocate to the char* struct member. and the answer was to use lazy/delayed allocation as of:

  1. void setName(Emp* emp, char* newName)
  2. {
  3.     free(emp->name);
  4.     emp->name = malloc(strlen(newName) + 1);
  5.     strcpy(emp->name, newName);
  6. }

(It seems to me to be the same idea used for Objective-C, the setter is release the previous pointer and then retain (in C to copy) the parameter pointer. So, the whole program will be:

  1. #include <stdio.h>
  2. #include <string.h>
  3. #include <stdlib.h>
  4. 
  5. typedef struct
  6. {
  7.     char* name;
  8. }Emp;
  9. 
 10. void init(Emp** emp)
 11. {
 12.     *emp = malloc(sizeof(Emp));
 13.     (*emp)->name = NULL;
 14.     (*emp)->name = malloc(sizeof(char*));
 15. }
 16. 
 17. void release(Emp** emp)
 18. {
 19.     free((*emp)->name);
 20.     free(*emp);
 21. }
 22. 
 23. void setName(Emp* emp, char* newName)
 24. {
 25.     free(emp->name);
 26.     emp->name = malloc(strlen(newName) + 1);
 27.     strcpy(emp->name, newName);
 28. }
 29. char* getName(Emp* emp)
 30. {
 31.     return emp->name;
 32. }
 33. 
 34. int main(void)
 35. {
 36.     Emp* emp;
 37.     init(&emp);
 38.     setName(emp, "Muhammad                              Abdullah");
 39.     printf("%s", getName(emp));
 40.     release(&emp);
 41.     
 42.     return 0;
 43. }

What if you forgot to deallocate reserved memory in your objective-c (c/c++) programs?

2011-09-11T23:25:00.000+02:00

The worst thing ever that I usually do is to forget to deallocates memory for objects I create when working with non-garbage collector languages (like C/C++/Objective C) So, That If I didn't de-allocate the memory .. what in that?? Actually it is a disaster ... Watch this example:

  1. #import <Foundation/Foundation.h>
  2. 
  3. int main(void)
  4. {
  5.     long long i;
  6.     for (i=0; i < 100000000000000; i++)
  7.     {
  8.         NSString* string = [[NSString alloc] initWithString :@"string"];
  9.         //[string release];
 10.     }
 11. 
 12.     [NSThread sleepForTimeInterval: 5];
 13.     
 14.     return 0;
 15. }

Then compile and run with GNUstep, the memory used by the program reaches 2 GB (I've 4 GB of RAM), and then the program terminates printing:

Virtual memory exhausted

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.

Remember, each time you enter a block of code (method for example) and allocate the miss to deallocate the memory you allocate will add this to the RAM and will not remove..finally you may find your program get crashed because it uses too much memory !

Wrappers in Objective-c

2011-09-10T19:09:00.000+02:00

  1. //string_2_primtiives.m
  2. #import <Foundation/Foundation.h>
  3. 
  4. /**
  5. *    You can convert the following to each other
  6. *    NSNumber <=> primitives <=> NSString 
  7. */
  8. 
  9. int main(void)
 10. {
 11.     NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
 12. 
 13.     //1- primitives => NSNumber
 14.     NSNumber* intNum = [NSNumber numberWithInteger: 20];
 15.     NSNumber* floatNum = [NSNumber numberWithFloat: 25.325];
 16.     
 17.     NSLog(@"%@ %@", intNum, floatNum);
 18.     
 19.     // 2- NSNumber => primitives:
 20.     int x = [intNum intValue];
 21.     float f = [floatNum floatValue];
 22.     // also, we can convert nay number object (regards of which value it contains) to any primitives type
 23.     //, and the standard C casting rules will be applied:
 24.     int x2 = [floatNum intValue];
 25.     
 26.     NSLog(@"%d %g %d", x, f, x2);
 27.     
 28.     // 3- primitives => NSString:
 29.     NSString* string = [NSString stringWithFormat: @"%d",x];
 30.     NSLog(@"%@", string);
 31.     
 32.     // 4- NSString = > primitives:
 33.     int i = [@"1" intValue];
 34.     float g = [@"13.4" floatValue];
 35.     int i2 = [@"13.4" intValue];
 36.     
 37.     NSLog(@"%d %g %d", i, g, i2);
 38.     
 39.     // 5- NSNumber => NSString
 40.     NSString* str = [NSString stringWithFormat:@"%@", [NSNumber numberWithBool:20]];
 41.     NSLog(@"%@", str);
 42.     
 43.     // 6- NSString => NSNumber 
 44.     NSNumber* charNum = [NSNumber numberWithChar: [@"20" intValue]];
 45.     NSLog(@"%@", charNum);
 46.     
 47.     [pool release];
 48.     return 0;
 49. }
 50. 
 51. /** output:
 52. 
 53. 20 25.325
 54. 20 25.325 25
 55. 20
 56. 1 13.4 13
 57. 1
 58. 20
 59. 
 60. */