To call a method we have to know the invocation object and its parameters.
Example: "xxx".concat("yyy")
Once the invocation object and the parameters are known, we can execute the method and compute the result.
Example: "xxx".concat("yyy")
returns the string "xxxyyy"
In this case, the evaluation of the invocation object and of the parameters is immediate. In general, both the invocation object and the parameters passed as arguments may need to be obtained by first calling other methods.