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We can use inbuilt lock provided by java.util.concurrent API
Or
We can use atomic variable

Immutability

If only thread communication is the requirement and not mutual exclusion then making the shared object volatile would suffice.

Make Objects as immutable

There is one more mechanism which wasn't mentioned in the comments.
java.util.concurrent.Semaphore
Maintains multiple permits. The number of permits is determined by a constructor parameter.

Semaphore s = new Semaphore(permits)

When the parameter is set to 1 than Semaphore behaves as Lock.