com.sforce.ws.ConnectionException: Check authEndpoint. It must contain '/services/Soap/u/' error in Java

Problem : If you are using partner wsdl and trying to access salesforce org using java code ,then at that time you may encounter this error if authEndpoint is wrong(https://login.salesforce.com/services/Soap/c/40.0).
Solution : If you are using partner wsdl,then authEndpoint url will be of this form
https://login.salesforce.com/services/Soap/u/40.0

If you use url like this "https://login.salesforce.com/services/Soap/c/40.0" for partner wsdl, then you get above error  because this url will be for Enterprise wsdl files.
Note: /services/u for Partner Wsdl.
/services/c for Enterprise wsdl.

Note:Versions may change for example https://login.salesforce.com/services/Soap/u/39.0 or https://login.salesforce.com/services/Soap/u/38.0 etc.