JCF: user defined collections

Transcription

1 JCF: user defined collections Bruce Eckel, Thinking in Java, 4th edition, PrenticeHall, New Jersey, cf. José Valente de Oliveira 20-1 Developing of a user-defined random queue n A random queue is a queue whose elements are randomly selected to be outputted n A random queue allows to access its elements randomly n Our goal is to develop a random queue where both input and output operate in constant time jvo@ualg.pt José Valente de Oliveira

2 Interface hierarchy Interface Queue interface Queue<E> extends Collection<E> { E element(); E peek(); E remove(); E pool(); boolean offer(e element); Throws exception Returns special value (null) Insert add(e) offer(e) Remove remove() poll() Examine element() peek() jvo@ualg.pt José Valente de Oliveira

3 Interface Collection public interface Collection<E> extends Iterable<E> { // Basic operations int size(); boolean isempty(); boolean contains(object element); boolean add(e element); //optional boolean remove(object element); //optional Iterator<E> iterator(); // Bulk operations boolean containsall(collection<?> c); boolean addall(collection<? extends E> c); //optional boolean removeall(collection<?> c); boolean retainall(collection<?> c); void clear(); // Array operations Object[] toarray(); <T> T[] toarray(t[] a); //optional //optional //optional optional -> UnsupportedOperationException jvo@ualg.pt José Valente de Oliveira 20-5 Interface hierarchy and abstract classes 3

4 public abstract class AbstractCollection<E> extends Object implements Collection<E> n This class provides a skeletal implementation of the Collection interface, to minimize the effort required to implement this interface. To implement an unmodifiable collection, the programmer needs only to extend this class and provide implementations for the iterator and size methods. (The iterator returned by the iterator method must implement hasnext and next.) To implement a modifiable collection, the programmer must additionally override this class's add method (which otherwise throws an UnsupportedOperationException), and the iterator returned by the iterator method must additionally implement its remove method. The programmer should generally provide a void (no argument) and Collection constructor, as per the recommendation in the Collection interface specification. The documentation for each non-abstract method in this class describes its implementation in detail. Each of these methods may be overridden if the collectionbeing implemented admits a more efficient implementation. jvo@ualg.pt José Valente de Oliveira 20-7 public abstract class AbstractQueue<E> extends AbstractCollection<E> implements Queue<E> n This class provides skeletal implementations of some Queue operations. The implementations in this class are appropriate when the base implementation does not allow null elements. Methods add, remove, and element are based on offer, poll, and peek, respectively but throw exceptions instead of indicating failure via false or null returns. A Queue implementation that extends this class must minimally define a method Queue.offer(E) which does not permit insertion of null elements, along with methods Queue.peek(), Queue.poll(), Collection.size(), and a Collection.iterator() supporting Iterator.remove(). jvo@ualg.pt José Valente de Oliveira

5 RandomQueue package ualg.deei; import java.util.*; pubic class RandomQueue<E> extends AbstractQueue<E> implements Queue<E> { private int actsize=0; private List<E> rq; public RandomQueue() { rq = new ArrayList<E>(); public RandomQueue(int n) { rq = new ArrayList<E>(n); public int size() { return actsize; jvo@ualg.pt José Valente de Oliveira 20-9 Interface Queue interface Queue<E> extends Collection<E> { E element(); E peek(); E remove(); E pool(); boolean offer(e element); Throws exception Returns special value (null) Insert add(e) offer(e) Remove remove() poll() Examine element() peek() jvo@ualg.pt José Valente de Oliveira

6 RandomQueue /** Insert an element at the end of the queue */ public boolean offer(e e) { if(e==null) returnfalse; // por imposição da interface rq.add(actsize++, e); return true; // assume-se capacidade ilimitada jvo@ualg.pt José Valente de Oliveira RandomQueue /** returns an element randomly without affecting the state of the isempty() == 0 By interface requirement returns null if queue is empty. */ public E peek() { if (actsize==0) returnnull; int r = (int) (Math.random()) * actsize; return rq.get(r); jvo@ualg.pt José Valente de Oliveira

7 RandomQueue a randomly selected element removing it from the queue. elements are uniformly selected, i.e., with equal probability */ public E poll() { if (actsize == 0) return null; int r=(int) (Math.random() * actsize); E tmp = rq.get(r); rq.set(r, rq.get(--actsize)); // rq.set(actsize+1, null); return tmp; jvo@ualg.pt José Valente de Oliveira RandomQueue /* Optou-se por percorrer sequencialmente o conteúdo da fila aleatória Iterações sucessivas produzem a mesma sequência de elementos. */ public Iterator<E> iterator() { return new Iterator<E> () { int i=0; public boolean hasnext() { return i < actsize; public E next() throws NoSuchElementException { if(i >= actsize) throw new NoSuchElementException("At the end!"); return rq.get(i++); public void remove() throws IllegalStateException { if (i==0) throw new IllegalStateException ("call next() first!"); rq.remove(i-1); ; // end of class jvo@ualg.pt José Valente de Oliveira

8 RandomQueue: making it available n Make a jar file, say lib.jar jar cvf lib.jar ualg\deei\*.class n Make the lib.jar file available from a given dir, say: c:\mydistribution n Set the CLASSPATH environment variable to include the above dir: set CLASSPATH=%CLASSPATH%;c:\myDistribution\lib.jar;.; jvo@ualg.pt José Valente de Oliveira RandomQueue: making a java extension (optional package) n n Make a jar file, say lib.jar jar cvf lib.jar ualg\deei\*.class (Java 6 or later) Make the lib.jar file available from the following dir System.getProperties().getProperty( "java.ext.dirs")) q q q SolarisTM Operating System: /usr/jdk/packages/lib/ext Linux: /usr/java/packages/lib/ext Microsoft Windows: %SystemRoot%\Sun\Java\lib\ext jvo@ualg.pt José Valente de Oliveira

9 Application example using shuffle import java.util.*; class Peca { private int lado1, lado2; public Peca(int i, int j) {lado1=i; lado2=j; public String tostring(){ returnnew String("("+lado1 +" " + lado2+")"); public class ExDesord { public static void main(string[] args) { List<Peca> domino = new ArrayList<Peca>(28); for (int i = 0; i < 7; i++) for (int j = i; j < 7; j++) domino.add(new Peca(i,j)); System.out.print( Before: "); System.out.println(domino); Collections.shuffle(domino); System.out.print( After: "); System.out.print(domino); jvo@ualg.pt José Valente de Oliveira Application example using our RandomQueue for efficiency import java.util; import ualg.deei.randomqueue; public class RQClient { public static void main(string[] args) throws NoSuchElementException, IIlegalStateException { Queue<Peca> domino = new RandomQueue<Peca>(28); for (int i=0; i<7; i++) for(int j=i; j<7; j++) domino.offer(new Peca(i, j)); System.out.print(domino); jvo@ualg.pt José Valente de Oliveira

10 To take away today n JCF: defining and using user-defined collections q TheRandomQueue example jvo@ualg.pt José Valente de Oliveira JCF: Case studies jvo@ualg.pt José Valente de Oliveira

11 CS1: From real to fraction n How to convert a real number into a fraction? q 0.1=? q 0.25=? q = 0.(3) = 0.3 =? q = =? jvo@ualg.pt José Valente de Oliveira Exemplo 1: De real a fracção jvo@ualg.pt José Valente de Oliveira

12 Anthyphairetic Ratio José Valente de Oliveira Exemplo 1: De real a fracção jvo@ualg.pt José Valente de Oliveira

13 Exemplo 1: De real a fracção jvo@ualg.pt José Valente de Oliveira Exemplo 1: De real a fracção jvo@ualg.pt José Valente de Oliveira

14 Exemplo 1: De real a fracção jvo@ualg.pt José Valente de Oliveira Exemplo 1: De real a fracção jvo@ualg.pt José Valente de Oliveira