Discussion 2: Pointers Christine Zhou Agenda Announcements Review Worksheet Announcements Happy three-day weekend! HW1 due Friday 9/8 Proj0 due Tuesday 9/18 Get started ASAP! Labs are due at midnight on Fridays Discussion survey: tinyurl.com/czdisc2 Review: Defining Classes // class definition public class IntList { // instance variables int head; IntList tail; // constructors, which will create IntList objects public IntList() {...} public IntList(int value, IntList tail) {...} // you can create methods that use the instance variables! public void insert(int val) {...} public void removeLast() {...} } Review: Primitives and Reference Types Two types of values: primitives and reference types 8 primitive types: char, boolean, int, double, float, byte, short, long All others are reference types (Strings, self-defined classes like IntList) Pass-by-value When Java creates a primitive type value, it will create a box and store that primitive value in the box When Java creates a reference type value, it will create a box and store the pointer to the reference type value (the value in the box will be the address of the object in memory) Review: Box and Pointer Diagrams Will be very helpful in keeping track of everything! Small example with an int and a Potato object (with an int age and a String variety) Review: Box and Pointer Diagrams Let’s try a small example with the IntList we defined a few slides ago. Draw the B&P for the following code: IntList lst1 = new IntList(1, null); lst1 = new IntList(2, lst1); IntList lst2 = new IntList(3, null); lst2 = new IntList(4, lst2); lst2.head = lst1.head; lst2.tail = lst1.tail; Take the value living inside the box that we’re looking for, and then do the reassignment (pass-by-value of the box) 1. Boxes and Pointers Draw a box and pointer diagram to represent the IntLists after each statement. IntList L = IntList.list(1, 2, 3, 4); IntList M = L.tail.tail; IntList N = IntList.list(5, 6, 7);