NSStringの結合方法

NSString *object1 = [NSString stringWithCString:"ABC"];
NSString *object2 = [NSString stringWithCString:"DEF"];
NSString *object3 = [object1 stringByAppendingString:object2];
NSString *object4 = [NSString stringWithFormat:@"%@%@", object1, object2];
NSLog(@"%@%@", object1, object2);

stringByAppendingStringメソッドはインスタンス・メソッド
stringWithFormatはクラス・メソッド