Dates & ListsDate classesDateDateFormatDateFormatCalendarExampleFundamental AbstractionsCollection InterfacesCollectionSetListIteratorModifying CollectionsIterator ExampleListIteratorIterator ExampleCollection APIBulk Operation ExampleList APISublist ExampleImplementationsArrayListLinkedListBenchmarksSortingComparable interfaceComparatorReturn valueCollections MethodsExampleDates & ListsIS 313, 4.8.2003Date classes Date represents a point in time DateFormat a class (abstract) that formats time and date information Calendar a class (abstract) that allows for date arithmeticDate current time Date d = new Date () other dates go through DateFormat or CalendarDateFormat Use static factory methodsDateFormat.getDateInstance Can specify short, medium, long or fullDateFormat.getDateInstance (DateFormat.SHORT) Can also specific localeDateFormat.getDateInstance(DateFormat.SHORT, Locale.ITALY) SimpleDateFormat for custom formatsnew SimpleDateFormat (“MM/dd/yyyy”)DateFormat With the date format parse strings containing dates output strings containing dates ParseDate date = df.parse (“11/12/1999”); FormatString dateString = df.format (date);Calendar Date/Calendar arithmetic What day of the week was 2/23/1995? What was the date 30 days later? Different calendars we use GregorianCalendarExample Date DateFormat SimpleDateFormat Calendar GregorianCalendarFundamental Abstractions Collection Any grouping of items Set Unordered, non-redundant List Ordered Map Object->Object mappingsCollection InterfacesCollection Perform operations that apply to any collection In many cases Distinction between Set and List is irrelevant Add an item Test to see if an Object is in the Collection Some operations not supported by all implementationsSet Has only the Collection methods But the Collection has no duplicatesList Adds to the Collection methods Positional access Search Range-view An enhanced IteratorIterator Moves through the elements of a Collection “consuming” = “moving” like reading data from a stream Methods hasNext(), next() remove() last item seenModifying Collections Iterator is like a pointer within the collection, but points “in between” entries Modification happens to last visited entryIterator ExampleListIterator Specific to List objects Set and add As well as remove Adds backward movement iter.prev(); modification still happens to last visited itemIterator Examplestatic void filter(Collection c) {for (Iterator i = c.iterator(); i.hasNext(); ) if (i.next().toString().indexOf(“Burke”) == -1)i.remove();}  What does it do? Works on any collection “for” skeletonCollection APIint size(); boolean isEmpty(); boolean contains(Object element); boolean add(Object element); // Optional boolean remove(Object element); // Optional Iterator iterator(); // Bulk Operations boolean containsAll(Collection c); boolean addAll(Collection c); // Optional boolean removeAll(Collection c); // Optional boolean retainAll(Collection c); // Optional void clear(); // Optional // Array Operations Object[] toArray(); Object[] toArray(Object a[]);Bulk Operation Examplec.removeAll(new Integer(0)); Remove all 0s from a Collection of Integer objects More about the Collections class laterList API// Positional Access Object get(int index); Object set(int index, Object element); // Optional void add(int index, Object element); // Optional Object remove(int index); // Optional boolean addAll(int index, Collection c); // Optional // Search int indexOf(Object o); int lastIndexOf(Object o); // Iteration ListIterator listIterator(); ListIterator listIterator(int index); // Range-view List subList(int from, int to);Sublist Examplepublic static List dealHand(List deck, int n){int deckSize = deck.size();List handView = deck.subList(deckSize-n, deckSize);List hand = new ArrayList(handView);handView.clear();return hand;}Implementations Interfaces do not give us objects Need specific implementations to do what the interfaces specify Java has multiple implementations for most interfaces Reason Performance tradeoffsArrayList Vector-like O(n) delete and insert except at end Good for most purposesLinkedList Slower at positional access O(n) vs O(1) Insert / remove advantageBenchmarks11017075801870LinkedList47801920270110ArrayListRemoveInsertIterationGetTypeSorting Collections utility methods include sorting Collections.sort (c) To sort, we need an order What takes precedence over what No universal order possibleComparable interfacepublic interface Comparable{ public int compareTo(Object o);} Your class must implement in order to be sortable Static method in Collections class Collections.sort (myCollection); error if objects in myCollection don’t implement Comparable if contents of myCollection aren’t comparable to each otherComparator Comparable interface = “natural order” Sometimes multiple ordering possibles A separate class called a comparatorpublic interface Comparator { int compare(Object o1, Object o2);} Note Comparable = 1 argument, Comparator = 2 argsReturn value int return value -1 means “less than” 0 means “equal” should match == +1 means “greater than” in compareTo -1 means this < argument in compare -1 means o1 < o2Collections Methods binarySearch copy fill max min reverse shuffle singleton sortExample List ArrayList Iterator Collections.sort Comparable