class method

CompositURL.m

#import "CompositURL.h"
#import "Defines.h"

@implementation CompositURL

//Composit URL Programation
+ (NSURL *) compositWithStr:(NSString *)strUrl{
    NSString *strUrl = @"host";
    strUrl = [strUrl stringByAppendingFormat:@"%@.json",strUrl];
    NSURL *url = [[NSURL alloc]initWithString:strUrl];
    return url;
}

main.m

#import "Test.h"
#import "CompositURL.h"


@implementation Test

//Composit URL Programation
- (void)someMethod{
  NSURL *url = [CompositeURL compositWithStr:@"tesst"];
  //do what you want

}