Circular linked list in Objective C

gistfile1.m

//
//  CircularLinkedList.h
//  learnObjectiveC
//
//  Created by kmd on 2/28/15.
//  Copyright (c) 2015 Happy Days. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface CircularLinkedList : NSObject
+(CircularLinkedList*)initialize;
-(void) insertFront:(NSInteger)value;
-(void) displayNodes;
-(void) deleteFrontNode;
@end


//
//  CircularLinkedList.m
//  learnObjectiveC
//
//  Created by kmd on 2/28/15.
//  Copyright (c) 2015 Happy Days. All rights reserved.
//

#import "CircularLinkedList.h"

@interface CNode : NSObject
@property (nonatomic, strong) CNode *link;
@property (nonatomic, strong) id data;
@end

@implementation CNode
@end

@interface CircularLinkedList ()
@property (nonatomic, strong) CNode* last;
@property (nonatomic, strong) CNode* first;
@end

@implementation CircularLinkedList
+(CircularLinkedList*)initialize {
    static CircularLinkedList *circularLinkedList;
    if (!circularLinkedList) {
        circularLinkedList = [CircularLinkedList new];
    }
    return circularLinkedList;
}

-(void) insertFront:(NSInteger)value {
    CNode* temp = [CNode new];
    temp.data = [NSNumber numberWithInteger:value];
    if (self.first == nil && self.last == nil) {
        self.first = temp;
        self.last = temp;
    } else {
        CNode *tail = self.last;
        tail.link = temp;
        temp.link = self.first;
        self.last = temp;
    }
}

-(void) deleteFrontNode {
    if (self.last == nil && self.first == nil) {
        NSLog(@"nothing to delete");
    } else {
        self.last.link = self.first.link;
    }
}
-(void) displayNodes {
    CNode *temp;
    if (self.last == NULL) {
        NSLog(@"empty");
    } else {
        for (temp = self.last.link; temp!= self.last; temp=temp.link) {
            NSLog(@"%@", temp.data);
        }
        NSLog(@"%@", temp.data);
    }
}
@end