There is a long tradition for Apple to have 2 major event in each year, where one is the World Wide Developer Conference (WWDC) that usually falls on May and product launch during the autumn period. According to MacRumors, the WWDC18 will be hosted at McEnery exhibition center located at San Jose California.
After digging through the McEnery center reservation list by MacRumors, 3 of the 4 weeks on June 2018 has been booked by other parties and hence the WWDC is speculated to commence from 4th to 8th June, if according to its previous trend.
If WWDC goes within expectation, the new iOS 12, macOS 10.14, tvOS and new watchOS is expected to launch during the stipulated period. There might be new iPhone SE2 and 13 inches Macbook to launch along with Macbook Pro, Mac Pro and iPad Pro.
The seats for WWDC is extremely limited as there will be 5000 developers and 1000 software engineer tickets available and starts from US$1599.