int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSObject* obj = @"hello";
        //強制型別轉化成NSString
        NSString* str = (NSString*)obj;
        NSLog(@"轉換後：%@",str);
       
        NSObject* obj2 = @"hello";
        //強制型別轉化成NSArray
        NSArray* arr = (NSArray*)obj2;
        //報錯，arr實際指向的是NSString物件
        NSLog(@"轉換後：%@",[arr count] );
    }
}

 

        NSObject* obj = @"Hello";
        //isKindOfClass
        //判斷obj是否是NSString類或其子類的例項,輸出true
        NSLog(@"%d",[obj isKindOfClass:[NSString class]]);
        //判斷obj是否是NSObject類或其子類的例項,輸出true
        NSLog(@"%d",[obj isKindOfClass:[NSObject class]]);
        //判斷obj是否是NSObject類或其子類的例項,輸出false
        NSLog(@"%d",[obj isKindOfClass:[NSArray class]]);
       
       
        //判斷NSString是否是NSObject類的子類 輸出true
        NSLog(@"%d",[NSString isSubclassOfClass:[NSObject class]]);