java - Mockito error with method that returns Optional<T> -

i have interface following method

public interface iremotestore {  <t> optional<t> get(string cachename, string key, string ... rest);  } 

the instance of class implementing interface called remotestore.

when mock mockito , use method when:

mockito.when(remotestore.get("a", "b").thenreturn("lol"); 

i error:

cannot resolved method 'thenreturn(java.lang.string)'

i thought has fact returns instance of optional class tried this:

mockito.<optional<string>>when(remotestore.get("cache-name", "cache-key")).thenreturn         (optional.of("lol")); 

but, error instead:

when (optional '<'string'>') in mockito cannot applied (optional'<'object'>').

the time worked this:

string returncachevaluestring = "lol"; optional<object> returncachevalue = optional.of((object) returncachevaluestring); mockito.<optional<object>>when(remotestore.get("cache-name", "cache-key")).thenreturn(returncachevalue); 

but above returns instance of optional '<'object'>' , not optional '<'string'>.

why couldn't return instance of optional '<'string'>' directly? if could, how should go doing that?

mocks return have expectation return type matches mocked object's return type.

here's mistake:

mockito.when(remotestore.get("a", "b")).thenreturn("lol"); 

"lol" isn't optional<string>, won't accept valid return value.

the reason worked when did

optional<object> returncachevalue = optional.of((object) returncachevaluestring); mockito.<optional<object>>when(remotestore.get("cache-name", "cache-key")).thenreturn(returncachevalue); 

is due returncachevalue being optional.

this easy fix: change optional.of("lol") instead.

mockito.when(remotestore.get("a", "b")).thenreturn(optional.of("lol")); 

you can away type witnesses well; result above inferred optional<string>.