About Question enthuware.ocpjp.v8.2.1847 :

[Ad9999]

So basically if you wanted Collectors.toMap to ignore duplicate key entries you'd pass in something like (a,b) -> a for the BinaryOperator argument.

[sreeharshitha]

as both collect and forEach are terminal operations, doesn't the code result in compilation error?

[admin]

The code is not calling two terminal operations on the same stream. The call to collect returns a Map and forEach is called on that Map.
You might want to try compiling and running the code.