I have a very simple java code like this. I don't have any idea how to do this in Objective C. Especially, the static part which calls the getLocalAddress() method and assign it into the static string variable. I know how to set a static variable and a static method in Objective but I dont know how to implement that static { } part in java. Thanks in advance...

public class Address {

     public static String localIpAddress;

    static {
        localIpAddress =  getLocalIpAddress();
    }

    public Address() {

    }

    static String getLocalIpAddress() {
         //do something to get local ip address
     }

}

I added this in my .h file

 #import <Foundation/Foundation.h>

 extern NSString *localIpAddress;

 @class WifiAddrss;

 @interface Address : NSObject {

 }

 @end

And my .m file looks like

 #import "Address.h"
 #import "WifiAddress.h"

 @implementation Address

 +(void)initialize{
     if(self == [Address class]){
         localIpAddress = [self getLocalIpAddress];
     }
 }

 +(NSString *)getLocalIpAddress{
      return address here
 }

 -(id)init{    
     self = [super init];
     if (self == nil){
         NSLog(@"init error");
     }

     return self;
 }
 @end

And Now I am getting a linking error and it complains about "extern NSString *localIpAddress" part. If I change the extern to static, it works fine. But what I wanted to do is that I want make the scope of "localIpAddress" variable as grobal. Since if I put "static" in front of a variable in Objective-C then the variable is only visible in the class. But this time, I want to make that as a grobal variable. So my question is how to make "localIpAddress" variable as a grobal variable which is initialized once when the first time Address class is created.. Thanks in advance...