Call Pass by Value

When you pass an object as an argument, remember that the argument and the parameter are not the same variable. Instead, there are two variables (one in the caller and one in the callee) that have the same value, at least initially. For example we can draw a stack diagram for the last GetDistance call in our last example:

In this case, the variable values are the same. However if GetDistance happened to change one of the instance variables of First or Second , it would have no effect on Start and Current . Of course, there is no reason for GetDistance to modify its parameter, so this isolation between the two functions is appropriate.

This kind of parameter-passing is called “pass by value” because it is the value of the class (or other type) that gets passed to the function.