集合相互转换

        //1.NSArray 转换成 NSMutableArray
        NSArray * array = @[@"one",@"two",@"three"];
        NSMutableArray * muArray = [NSMutableArray arrayWithArray:array];
        NSLog(@"muarray %@",muArray);

        //2.NSDictonary 转换成        NSMutableDictionary
        NSDictionary * dic = @{@"one":@"1",@"two":@"2"};
        NSMutableDictionary * muDic = [NSMutableDictionary dictionaryWithDictionary:dic];
        NSLog(@"mudic %@ ",muDic);

        //3.NSset 转换成 NSMutableSet
        NSSet * set = [[NSSet alloc] initWithObjects:@"one",@"two", nil];
        NSMutableSet *muSet = [NSMutableSet setWithSet:set];
        NSLog(@"muSet %@",muSet);

        //4.NSArray 转换成NSSet
        NSMutableSet * muSet2 = [NSMutableSet setWithArray:array];
        NSLog(@"muSet2 %@",muSet2);

        //5.NSDictionary 转化成NSArray
        NSArray * allkeys = [dic allKeys];
        NSLog(@"allkeys %@",allkeys);
        NSArray * allValues = [dic allValues];
        NSLog(@"allValues %@",allValues);

        //6.字符串转换成数组
        NSString * str = @"www.itacast.cn";
        NSArray * strArray =        [str componentsSeparatedByString:@"."];
        NSLog(@"strArray %@",strArray);