Question: I have two DF's, DF A and DF B. Both have identical schema.
DF A's column C have a different value and DF B's column C have a different value, other data is exactly same. Now, If I want to combine both tables DF C, how to do it in spark? I tried to do join operation, but it is creating duplicate columns.
For example:
DF A:

`+---+----+
 | k| v|
 +---+----+
 | 1| |
 | 2|bar1|
 +---+----+`

DF B:

`+---+----+
 | k| v|
 +---+----+
 | 1|foo1|
 | 2| |
 +---+----+`
Expected result:
`+---+----+
| k| v|
+---+----+
| 1|foo1|
| 2|bar1|
+---+----+`

Answer: 
The system is looking for a main class `restaurantclient.RestaurantClient`, so a class `RestaurantClient` in package `restaurantClient`, but your class `RestaurantClient` seems to be in the default package.
try this if you are not getting any compilation issues.

You can :

1. RightClick on project node and go to Set configuration.
2. Select the main class for your application.
3. Then clean and build.

Even if the above steps don't work for you then then delete the Netbeans cache by deleting the (index) folder

Fore more details 
Follow the stackOverflow question 
[Netbeans - Error: Could not find or load main class](https://stackoverflow.com/questions/20034377/netbeans-error-could-not-find-or-load-main-class)