Introduction to Programming Languages/Object Oriented Programming

Objects as Functions (Conceptual Model) A useful abstraction:message → response Meaning: You send a message (getData) The object returns a response ("Hello") Example — Java class Node { private String data; private Node link; public Node(String data, Node link) { this.data = data; this.link = link; } public String getData() { return data; } }Here: Message → getData() Response → String Same idea in SML (OO simulation) datatype message = GetData | GetLink; datatype response = Data of string | Object of message -> response; fun node data link GetData = Data data | node data link GetLink = Object link;The “object” is literally a function:message -> responseLimitation: No strong compile-time checking for valid messages OO in ML vs Java MLJAVA Functional language OO is not native Can simulate OO Built-in OO support But does NOT enforce OO style Non-OO Programming in Java Classes used as data structures class Node { public String data; public Node link; } Problems: No encapsulation Data is exposed Behavior outside objects static void add(Stack s, String data) { Node n = new Node(); n.data = data; n.link = s.top; s.top = n; }Problem: Data and behavior are separated Not truly OO