Method Invocation is when you give a call to method
Message Passing is passing objects as parameters (to a method)
class A
{
public void Method(Object obj)
{
}
}
class B
{
Object obj1 = new Object();
A a = new A();
a.Method1(obj1);
}
In the above example a.Method1() is Method invocation
passing parameter (obj1) to Method1 is message passing