{small lecturenumber - hepage :} The ArrayList class{small lecturenumber - hepage :} The ArrayList class{small lecturenumber - hepage :} The ArrayList class{small lecturenumber - hepage :} Comparison with Arrays{small lecturenumber - hepage :} Accessing elements{small lecturenumber - hepage :} Exercise 1{small lecturenumber - hepage :} Iterators{small lecturenumber - hepage :} Example{small lecturenumber - hepage :} Exercise 2{small lecturenumber - hepage :} Finding elements{small lecturenumber - hepage :} Exercise 3{small lecturenumber - hepage :} Other methods{small lecturenumber - hepage :} Specifying element types{small lecturenumber - hepage :} Exercise 4{small lecturenumber - hepage :} ArrayList vs arraysIntro to Programming IIArrayListsChris BrooksDepartment of Computer ScienceUniversity of San FranciscoDepartment of Computer Science — University of San Francisco – p. 1/??8-2: The ArrayList class•Last time, we learned about how to use arrays in Java.•Java also provides an ArrayList class that can help managearrays.•ArrayList is a generic container.◦That means that we can use the same container to storedifferent kinds of elements.Department of Computer Science — University of San Francisco – p. 2/??8-3: The ArrayList class•An example:ArrayList band = new ArrayList(3);band.add(‘‘john’’);band.add(‘‘paul’’);band.add(‘‘george’’);band.add(‘‘ringo’’);Department of Computer Science — University of San Francisco – p. 3/??8-4: The ArrayList class•Notice that we declared an initial array size.•The array is then able to grow dynamically beyond that.◦It’s better to allocate in advance if we can.•We can also remove elements, and access them.•We can also add in the middle of a list: band.add(1,‘‘ringo’’);Department of Computer Science — University of San Francisco – p. 4/??8-5: Comparison with Arrays•With arrays, we’d need to allocate a new array and copyeverything over. (yuck!)int []array1 = new int[5];for (i = 0; i < 5; i++) {array1 = i;}int []array2= new int[10];for (i = 0; i < 5; i++) {array2[i] = array1[i];}array1 = array2;Department of Computer Science — University of San Francisco – p. 5/??8-6: Accessing elements•get(index) lets us access the element at a particular index.•Elements in an ArrayList are stored as Objects.•This means that we need to cast them back to Strings.•Can’t store primitives.String name = (String)band.get(2);Department of Computer Science — University of San Francisco – p. 6/??8-7: Exercise 1•Redo the Student exercise from Monday using an ArrayList.◦Prompt the user for a number of students.◦Store the students in an ArrayList.◦Print them out in order.Department of Computer Science — University of San Francisco – p. 7/??8-8: Iterators•It can be cumbersome to iterate through a list using integers.•What if the size of the list changes while we’re iterating over it?•Why do we need to know the size of the array to do somethingto each element?•Java provides an abstraction for us known as an iterator.Department of Computer Science — University of San Francisco – p. 8/??8-9: ExampleList myList = ArrayList(10);// fill in the listListIterator i = myList.ListIterator();while (i.hasNext())System.out.println(i.next());Department of Computer Science — University of San Francisco – p. 9/??8-10: Exercise 2•Modify the previous code to use a ListIteratorDepartment of Computer Science — University of San Francisco – p. 10/??8-11: Finding elements•We can use indexOf to find where an element is located.•remove lets us remove things.int index = band.indexOf(‘‘ringo’’)band.remove(index)Department of Computer Science — University of San Francisco – p. 11/??8-12: Exercise 3•Add a method that allows the user to enter the name of astudent.•Loop through the array to find that student and remove them.•Now try doing it with indexOfDepartment of Computer Science — University of San Francisco – p. 12/??8-13: Other methods•also:◦size() - tells us how many elements are in the array.◦isEmpty() - tells us whether there’s anything in the list.◦contains(Object o) - tells us whether an object is in the list.◦clear() - removes everything.Department of Computer Science — University of San Francisco – p. 13/??8-14: Specifying element types•If we want to avoid casting elements, we can also define theArrayList to accept particular sorts of objects:◦Java 1.5 only ...ArrayList<String> al = new ArrayList<String>(3);al.add("john");al.add("paul");al.add("george");al.add("ringo");String name = al.get(2);System.out.println(name);Department of Computer Science — University of San Francisco – p. 14/??8-15: Exercise 4•Change your code to use the template notation, so that wedon’t have to cast everything anymore.Department of Computer Science — University of San Francisco – p. 15/??8-16: ArrayList vs arrays•ArrayLists manage inserting, searching, and removing for you.•Can grow dynamically.•Only work with objects, not primitives.•Provides some nice convenience methods.Department of Computer Science — University of San Francisco – p.
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