copyright by Scott GrissomCh 4 Grouping Objects Slide 1 Flexible-size Collections flexible collection of objects unlimited and unknown size iPod playlist as an example ArrayList provided in java.util.*; ArrayList playList; playList = new ArrayList (); Methods add(Object) // to end of list int size () Object get (int index) Object remove (int index) first item is in location zero Draw object diagram

copyright by Scott GrissomCh 4 Grouping Objects Slide 2 Processing Elements Cumbersome playList.get(0).play(); playList.get(1).play(); playList.get(2).play(); We need a flexible way to access each element even though we do not know how many For-each loop process each item in order until done for (Song s : playList){ s.play(); }

copyright by Scott GrissomCh 4 Grouping Objects Slide 3 Group Activity ArrayList stuff; Stuff = new ArrayList (); Stuff.add(“Howdy!”); Stuff.add(“My Name “); stuff.add(“is “); stuff.add(“Ralph”); stuff.remove(2); for(String str : stuff){ System.out.println(str); }

copyright by Scott GrissomCh 4 Grouping Objects Slide 4 While loop an alternative repetition structure int x = 0; while (x < 10){ System.out.println(x); } Advantages no collection required every element does not have to be processed Example Notebook search (p 94) Group exercises

copyright by Scott GrissomCh 4 Grouping Objects Slide 5 Auction System (4.10) Multiple classes Person contains a name Bid contains a value and Person Lot a description, lot #, high bid review the bidFor method Auction page 99 an ArrayList of logs and nextLotNumber review the bidFor method Group activities write additional methods 4.26 close 4.27 getUnsold() 4.30 removeLot()

copyright by Scott GrissomCh 4 Grouping Objects Slide 6 Fixed-size Collections called an array able to store objects or primitive types first element at location 0 uses a different syntax than ArrayList int [ ] nums; nums = new int [10]; used just as a variable nums[3] = 100; x = 5; nums[x] = 7; value = nums[x] + 8;

copyright by Scott GrissomCh 4 Grouping Objects Slide 7 for loop different syntax than for-each three parts for (int i = 0; i < 20; i++) System.out.println(i); for(index = 0; index < array.length; index++) total = total + array[index]; Group Activities sum average max min find

copyright by Scott GrissomCh 4 Grouping Objects Slide 8 Which loop? most are interchangeable while number of iterations is determined during performance for number of iterations is know before loop begins for-each process all elements of a collection