You don't need the local variable a,b,c, because all java functions pass primitive types by value (making a local copy of them). I would keep the same naming convention on setMaximum (calling the parameters a,b,c), because I see no reason to make it different from getMaximum and maximum. FInally I would get rid of maximum (not necessary), make setMaximum a void function (returns nothing) and decouple getMaximum from setMaximum (not calling setMaximum from inside it)and make it return maxVal instead of SetMaximum.

Edit. Another possible better solution would be to create a third function called calculateMaximum or something like that and put in it all the logic that it is currently in setMaximum. After it determines the greatest value it could call directly setMaximum that would have as it's only parameter the biggest value. In that case calculateMaximum would be void.
Or you can make it return the biggest value (in this case it won't be a void function), throw it in some variable and pass the variable as the argument for setMaximum, or be more direct and use determineMaximum as the argument of setMaximum, as it will return the maximum value that will be passed to setMaximum