1Java Collections FrameworkCS211Fall 20002Java Collections Framework■ Collections: holders that let you store and organize objects in useful ways for efficient access■ Since Java 1.2, the package java.util includes interfaces and classes for a general collection framework■ Goal: conciseness● A few concepts that are broadly useful● Not an exhaustive set of useful concepts■ Two types of concepts are provided● Interfaces (i.e., ADTs)● Implementations3JCF Interfaces and Classes■ Interfaces● Collection● Set (no duplicates)● SortedSet● List (duplicates OK)● Map (i.e., Dictionary)● SortedMap● Iterator● ListIterator■ Classes● HashSet● TreeSet● ArrayList● LinkedList● HashMap● TreeMap4java.util.Collection (an interface)public int size( );Return number of elements in collectionpublic boolean isEmpty( );Return true iff collection holds no elementspublic boolean add (Object x);Make sure the collection includes x; returns true if collection has changed (some collections allow duplicates, some don’t)public boolean contains (Object x);Returns true iff collection contains x (uses equals( ) method)public boolean remove (Object x);Removes a single instance of x from the collection; returns true if collection has changedpublic Iterator iterator ( );Returns an Iterator that steps through elements of collection5java.util.Iterator (an interface)public boolean hasNext ( );Returns true if the iteration has more elementspublic Object next ( );Returns the next element in the iteration; throws NoSuchElementException if no next elementpublic void remove ( );The element most-recently returned by next( ) is removed from the collection; can throw IllegalStateException if next( ) not yet used or if remove( ) already called6Additional Methods of Collectionpublic Object [ ] toArray ( );Returns a new array containing all the elements of this collectionpublic Object [ ] toArray (Object [ ] dest);Returns an array containing all the elements of this collection; uses dest as that array if it canBulk Operations:public boolean containsAll (Collection c);public boolean addAll (Collection c);public boolean removeAll (Collection c);public boolean retainAll (Collection c);public void clear ( );27java.util.Set (an interface)■ Set extends Collection● Set has no methods of its own, but it inherits the methods from Collection■ A Set contains no duplicates● If you attempt to add( ) an element twice then the second add( ) will return false (i.e., the Set has not changed)■ Write a method that checks if a given word is within a Set of words■ Write a method that removes all words longer than 5 letters from a Set■ Write methods for the union and intersection of two Sets8Set Implementations■ java.util.HashSet (a hashtable)● Constructorspublic HashSet ( );public HashSet (Collection c);public HashSet (int initialCapacity);public HashSet (int initialCapacity, float loadFactor);■java.util.TreeSet (a balanced BST [red-black tree])● Constructorspublic TreeSet ( );public TreeSet (Collection c);…■Both implement
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