Implements the List Interface  What is an interface?  all abstract methods  can not have instance variables  List is an interface  ArrayList implements List  What other interface have you seen?  Grid

ArrayList MethodsArrayList Methods  int size()  boolean add(E obj)  void add(int index, E obj)  E get(int index)  E set(int index, E obj)  E remove(int index)  void clear()

What can ArrayList hold?What can ArrayList hold?  Object references  No primitives!  Primitives are Auto-Boxed - converted to corresponding class (int to Integer, etc.)

Advantages / Disadvantages  Advantages  Easier to manipulate  Methods available to insert, delete, access  Easily /automatically resized  Disadvantages  One dimensional only  Can have ArrayLists of ArrayLists instead  Less efficient – space and time

Define import java.util.ArrayList; public class arrayListExample { private ArrayList B ; public arrayListExample() { B = new ArrayList (); B.add("tomato"); B.add("pear"); B.add("durian"); B.add("apple"); B.add("mango"); }

Populating private ArrayList card; card.add(0,55); // add 55 before 0 index card.add(99); // add 99 at end of list Finding Length int clen = card.size();

Accessing elements in a loop for ( int i = 0; i < stringList.size(); i++) { String item = stringList.get(i); System.out.println("Item " + i + " : " + item); } for ( String item: stringList){ System.out.println("retrieved element: " + item); }

ArrayList intList = new ArrayList (); int n = 1; boolean addMore = true; while (addMore) { intList.add(10 * n); n++; if (n == 100) addMore = false; }

For Each LoopFor Each Loop  Can’t be used to change an ArrayList object! List list = new ArrayList (); list.add("Hi"); … for (String s : list) s = "NO"; // does not change list objects

For Each LoopFor Each Loop  Can be used to mutate a referenced object! List bugs = new ArrayList (); bugs.add(new Bug()); … for (Bug b : bugs) b.setColor(Color.GREEN);// bugs are now green Can’t add or remove inside For-Each loop! Gets ConcurrentModificationException.

Generic TypesGeneric Types  Generic Types form a hierarchy (is-a).  Hierarchy is based on the base type.  Hierarchy is not based on the parameters to that type.  ArrayList is-a List  ArrayList is-not-a List

 ArrayList actors1 = new ArrayList (); // Good  ArrayList actors2 = new ArrayList (); // BAD  List actors3 = new ArrayList (); // Good  List actors4 = actors1;// BAD

Comparing List ElementsComparing List Elements ArrayList myList = new ArrayList (); // elements added to myList for (int idx=0; idx < myList.size(); i++) { if (myList.get(idx).equals(“monkey”) ) System.out.println(“Found a monkey”); }

Comparing List ElementsComparing List Elements ArrayList myList = new ArrayList (); // elements added to myList for (int idx=0; idx < myList.size(); i++) { if (myList.get(idx).compareTo(“monkey”) < 0) System.out.println(“Less than monkey”); if (myList.get(idx).compareTo(“monkey”) == 0) System.out.println(“Equals monkey”); if (myList.get(idx).compareTo(“monkey”) > 0) System.out.println(“More than monkey”); }

public class Student { private String name, school; private int grade; public Student( String nm, int gd, String sch) { //code to set all the instance variables} public String getName() { return name;} public int getGrade() { return grade;} public String getSchool() { return school;} public String toString() { return “Name: ” + getName() + “\n“ + “Grade: “ + getGrade() +“\n” + “School: “ + getSchool() + “\n\n”; }

public class SatSession2Roster { public static void main (String args[]) { ArrayList roster2 = new ArrayList (); }

Multiple Choice QuestionsMultiple Choice Questions

MC AnswersMC Answers  Q1: D // if 2 ones are next to each other the second one gets skipped.  Q2: D  Q3: B // one of the methods was a set() not an add()

Sample Free ResponseSample Free Response

Solution to FR Question PART A: public int getTotalBoxes() { int sum = 0; for (CookieOrder co : this.orders) { sum += co.getNumBoxes(); } return sum; }

PART B:PART B: public int removeVariety(String cookieVar) { int numBoxesRemoved = 0; for (int i = this.orders.size() - 1; i >= 0; i--) { if (cookieVar.equals(this.orders.get(i).getVariety())) { numBoxesRemoved += this.orders.get(i).getNumBoxes(); this.orders.remove(i); } return numBoxesRemoved; }

Alternative solution (forward traversal direction): public int removeVariety(String cookieVar) { int numBoxesRemoved = 0; int i = 0; while (i < this.orders.size()) { if (cookieVar.equals(this.orders.get(i).getVariety()) { numBoxesRemoved += this.orders.get(i).getNumBoxes(); this.orders.remove(i); } else i++; } return numBoxesRemoved; }