Let's try to write a method that swaps two employee objects:
public static void swap(Employee x, Employee y) // doesn't work
{
   Employee temp = x;
   x = y;
   y = temp;
}
If the Java programming language used call by reference for objects, this method would work:
Employee a = new Employee("Alice", . . .);
Employee b = new Employee("Bob", . . .);
swap(a, b);
// does a now refer to Bob, b to Alice?
However, the method does not actually change the object references that are stored in the variables a and b. The x and y parameters of the swap method are initialized with copies of these references. The method then proceeds to swap these copies.
// x refers to Alice, y to Bob
Employee temp = x;
x = y;
y = temp;
// now x refers to Bob, y to Alice
But ultimately, this is a wasted effort. When the method ends, the parameter variables x and y are abandoned. The original variables a and b still refer to the same objects as they did before the method call