CSC 1214: Object-Oriented Programming

Transcription

1 CSC 1214: Object-Oriented Programming J. Kizito Makerere University www: materials: e-learning environment: office: block A, level 3, department of computer science alt. office: institute of open, distance, and elearning, room 2 More on Collections Kizito (Makerere University) CSC 1214 March, / 24

2 Overview 1 Collections Collection Algorithms The Collection Interface The List Interface The Set Interface Comparators The Queue Interfaces and Classes The Collection Classes Lists and Sets 2 Maps The Map Interface SortedMap and Map.Entry Interfaces The Map Classes Hash- and Tree-Map 3 Homework Kizito (Makerere University) CSC 1214 March, / 24

3 Collections The Java collections framework (JCF) is a set of classes and interfaces that implement commonly reusable collection data structures This framework standardizes the way in which groups of objects are handled Although referred to as a framework, it works in a manner of a library Several standard implementations of a set of standard interfaces are provided You may also implement your own collection, if you choose In addition to collections, the framework defines several map interfaces and classes Maps store key/value pairs Kizito (Makerere University) CSC 1214 March, / 24

4 Collection Algorithms Collection Algorithms Chapter 15 of The Complete Reference Java TM 2, by Patrick Naughton & Herbert Schildt, Fifth Edition Algorithms are an important part of the collection mechanism Algorithms operate on collections and are defined as static methods within the Collection class Algorithms are available for all collections and provide a standard means of manipulating collections Several of the methods can throw: 1 a ClassCastException, which occurs when an attempt is made to compare incompatible types 2 an UnsupportedOperationException, which occurs when an attempt is made to modify an unmodifiable collection We shall discuss exception handling in the next lecture Collection defines three static variables: EMPTY SET, EMPTY LIST, and EMPTY MAP, which was added by Java 2, version 1.3 Kizito (Makerere University) CSC 1214 March, / 24

5 The Collection Interface Collections The sub interfaces of the java.util.collection interface Collection: At the top of the collections hierarchy. Enables you to work with groups of objects List: Extends Collection to handle sequences (lists of objects) Set: Extends Collection to handle sets, which must contain unique elements SortedSet: Extends Set to handle sorted sets Kizito (Makerere University) CSC 1214 March, / 24

6 The Collection Interface Collections The Collection Interface Methods boolean add(object obj) boolean addall(collection c) void clear() boolean contains(object obj) boolean containsall(collection c) boolean equals(object obj) int hashcode() boolean isempty() Iterator iterator() boolean remove(object obj) boolean removeall(collection c) boolean ratainall(collection c) int size() Object[] toarray() Object[] toarray(object array[]) Kizito (Makerere University) CSC 1214 March, / 24

7 The List Interface Collections The List Interface void add(int index, Object obj) boolean addall(int index, Collection c) Object get(int index) int indexof(object obj) int lastindexof(object obj) ListIterator listiterator() ListIterator listiterator(int index) Object remove(int index) Object set(int index, Object obj) List sublist(int start, int end) Kizito (Makerere University) CSC 1214 March, / 24

8 The Set Interface Collections The Set Interface Defines a set Extends Collection Declares the behavior of a collection that does not allow duplicate elements The add() method returns false if an attempt is made to add duplicate elements Does not define any additional methods of its own Kizito (Makerere University) CSC 1214 March, / 24

9 The Set Interface The Set Interface The SortedSet Interface Methods Comparator comparator() Object first() SortedSet headset(object end) Object last() SortedSet subset(object start, Object end) SortedSet tailset(object start) Kizito (Makerere University) CSC 1214 March, / 24

10 Comparators The SortedSet Interface Comparators A Comparator defines precisely what sorted order means In other words imposes a total ordering on some collection of objects Comparators can be passed to a sort method (such as Collections.sort or Arrays.sort) to allow precise control over the sort order They can also be used to control the order of certain data structures (such as sorted sets or sorted maps), or to provide an ordering for collections of objects that don t have a natural ordering Define two methods: compare() and equals() int compare(object obj1, Object obj2) boolean equals(object obj) Examples 1 x.equals(y) 2 c.compare(x, y) == 0 3 a.equals(b) && c.compare(a, b)!= 0 Kizito (Makerere University) CSC 1214 March, / 24

11 The Queue Interfaces and Classes Collections The Queue Interfaces and Classes Kizito (Makerere University) CSC 1214 March, / 24

12 The Collection Classes Collections The Collection Classes AbstractCollection: Implements most of the Collection interface AbstractList: Extends AbstractCollection and implements most of List interface AbstractSequentialList: Extends AbstractList for use by a collection that uses sequential rather than random acces of its elements LinkedList: Implements a linked list by extending AbstractSequentialList ArrayList: Implements a dynamic array by extending AbstractList AbstractSet: Extends AbstractCollection and implements most of the Set interface HashSet: Extends AbstractSet for use with a hash table TreeSet: Implements a set stored in a tree. Extends AbstractSet Kizito (Makerere University) CSC 1214 March, / 24

13 Lists and Sets The Collection Classes The ArrayList and LinkedList Classes ArrayList Constructors: ArrayList() ArrayList(Collection c) ArrayList(int capacity) Resize collection void ensurecapacity(int cap) void trimtosize() LinkedList Constructors: LinkedList() LinkedList(Collection c) Additional methods: void addfirst(object obj) void addlast(object obj) Kizito (Makerere University) CSC 1214 March, / 24

14 Lists and Sets The Collection Classes The HashSet and TreeSet Classes HashSet TreeSet Constructors HashSet() HashSet(Collection c) HashSet(int capacity) HashSet(int capacity, float fillratio) fillratio (also called load capacity) between 0 and 1. Default: 0.75 Load capacity determines how full the hash set can be before it is resized upward No additional methods HashSet does not guarantee the order of its elements Constructors: TreeSet() TreeSet(Collection c) TreeSet(Comparator comp) TreeSet(SortedSet ss) No additional methods Kizito (Makerere University) CSC 1214 March, / 24

15 Lists and Sets Collection Interfaces and Implementations In lecture 2, we saw how to access a Collection via an Iterator Kizito (Makerere University) CSC 1214 March, / 24

16 Maps Maps Aside from the java.util.collection interface, the Java JDK has the java.util.map interface as well It is sometimes also called an Associated Array or a Dictionary A map is an object that stores associations between keys and values, or key/value pairs Given a key, you can find its value Keys and values are objects Keys are unique Values may be duplicated Implementations of the Map interface do not contain collections of objects instead they contain collections of key->value mappings It can be thought of as an array where the index doesn t need to be an integer Kizito (Makerere University) CSC 1214 March, / 24

17 Maps The Map Interface Maps The Map Interface Map: Maps unique keys to values Map.Entry: Describes an element (a key/value pair) in a map. This is an inner class of Map SortedMap: Extends Map so that the keys are maintained in ascending order Kizito (Makerere University) CSC 1214 March, / 24

18 Maps The Map Interface Maps The Map Interface Methods void clear() boolean containskeys(object k) boolesn containsvalue(object v) Set entryset() boolean equals(object obj) Object get(object k) int hashcode() boolean isempty() Set keyset() Object put(object k, Object v) void putall(map m) Object remove(object k) int size() Collection values() Kizito (Makerere University) CSC 1214 March, / 24

19 Maps SortedMap and Map.Entry Interfaces The Map Interface SortedMap and Map.Entry Interfaces SortedMap Comparator comparator() Object firstkey() SortedMap headmap(object end) Object lastkey() SortedMap submap(object start, Object end) SortedMap tailmap(object start) Map.Entry Boolean equals(object obj) Object getkey() Object getvalue() int hashcode() Object setvalue(object v) Kizito (Makerere University) CSC 1214 March, / 24

20 Maps The Map Classes Maps The Map Classes AbstractMap: Implements most of the Map interfaces HashMap: Extends AbstractMap to use a hash table TreeMap: Extends AbstractMap to use a tree WeakHashMap: Extends AbstractMap to use a hash table with weak keys Kizito (Makerere University) CSC 1214 March, / 24

21 Maps Hash- and Tree-Map The Map Classes The HashMap and TreeMap Interfaces HashMap Constructors: HashMap() HashMap(Map m) HashMap(int capacity) HashMap(int capacity, float fillratio) Does not add any methods of its own Does not guarantee the order of its elements TreeMap Constructors: TreeMap() TreeMap(Comparator comp) TreeMap(Map m) TreeMap(SortedMap m) Does not define any additional methods of its own Kizito (Makerere University) CSC 1214 March, / 24

22 Maps Hash- and Tree-Map Maps class- and interface hierarchy of java.util.map Kizito (Makerere University) CSC 1214 March, / 24

23 Homework Homework Read about Class Libraries, Packages, and how to write GUI Applications Extra notes have been uploaded for this purpose Until now, the example programs we have explored have been text-based They are called command-line applications, which interact with the user using simple text prompts You are going to examine some Java applications that have graphical components These components will serve as a foundation to programs that have true Graphical User Interfaces (GUIs) Kizito (Makerere University) CSC 1214 March, / 24

24 Homework Assignment II Counters Interfaces and Inheritance in the Java Language Due Monday 26 th March 2018 public interface Counter { void increment(); void decrement(); void reset(); } String valueasstring(); class IntCounter implements Counter { // Your 1 st task is to implement this } class AsciiCounter implements Counter { // 2. Implement this too } class DateCounter implements Counter { // 3. Implement this too } class SequenceCounter implements Counter { // 4. Implement this too } class HexCounter extends IntCounter { /* 5. Implement this too * Note that this is a * subclass of IntCounter */ } Kizito (Makerere University) CSC 1214 March, / 24