Estrutura com iterador-1

Transcription

1 Estrutura com iterador-1 public class MyContainer Object [ ] items; int size; public Object get( int idx )... public boolean add( Object x )... public MyContainerIterator iterator( ) return new MyContainerIterator(this); public class MyContainerIterator private int current = 0; private MyContainer container; MyContainerIterator(MyContainer c) container = c; public boolean hasnext( ) return current < container.size; public Object next( ) return container.items[ current++ ]; Estrutura com iterador-2 public class MyContainer private Object [ ] items = new Object[ 5 ]; private int size = 0; public Iterator iterator( ) return new MyContainerIterator(this); public interface Iterator boolean hasnext(); Object next(); class MyContainerIterator implements Iterator private int current = 0; private MyContainer container; MyContainerIterator(MyContainer c) container = c; public boolean hasnext( ) return current < container.size; public Object next( ) return container.items[ current++ ]; -1

2 Estrutura com iterador-3 package weiss.ds; public class MyContainer private Object [ ] items = new Object[ 5 ]; private int size = 0; //... public Iterator iterator( ) return new LocalIterator(this); private static class LocalIterator implements Iterator private int current = 0; private MyContainer container; private LocalIterator( MyContainer c) container = c; public boolean hasnext( ) return current < container.size; public Object next( ) return container.items[ current++ ]; Estrutura com iterador-4 package weiss.ds; public class MyContainer private Object [ ] items = new Object[ 5 ]; private int size = 0; public Object get( int idx )... public boolean add( Object x )... public Iterator iterator( ) return new LocalIterator( ); private class LocalIterator implements Iterator private int current = 0; public boolean hasnext( ) return current < size; public Object next( ) return items[ current++ ]; -2

3 Iteradores Solução 1 Classes públicas para iterador e contentor Referência do iterador no contentor Iterador partilha dados do contentor Utilizador do contentor tem de definir iterador adequado Solução 2 Contentor devolve iterador genérico, programador usa interface Iterator iterator() é fábrica que produz iterador cujo tipo fica escondido do utilizador Solução 3 Classe do iterador é nested class no contentor Evita partilha de dados no package Iterador é objecto independente construído com referência ao contentor Solução 4 Classe do iterador é inner class do contentor Iterador está implicitamente associado ao contentor, e refere directamente os seus membros package weiss.util; public abstract class implements Collection * Tests if this collection is empty. public boolean isempty( ) return size( ) == 0; * Change the size of this collection to zero. public void clear( ) Iterator itr = iterator( ); while( itr.hasnext( ) ) itr.next( ); itr.remove( ); -3

4 * Obtains a primitive array view of the collection. the primitive array view. public Object [ ] toarray( ) Object [ ] copy = new Object[ size( ) ]; Iterator itr = iterator( ); int i = 0; while( itr.hasnext( ) ) copy[ i++ ] = itr.next( ); return copy; * Returns true if this collection contains x. * If x is null, returns false. * (This behavior may not always be appropriate.) x the item to search for. true if x is not null and is found in * this collection. public boolean contains( Object x ) if( x == null ) Iterator itr = iterator( ); while( itr.hasnext( ) ) if( x.equals( itr.next( ) ) ) return true; -4

5 * Removes non-null x from this collection. * (This behavior may not always be appropriate.) x the item to remove. true if remove succeeds. public boolean remove( Object x ) if( x == null ) Iterator itr = iterator( ); while( itr.hasnext( ) ) if( x.equals( itr.next( ) ) ) itr.remove( ); return true; * Return true if items in other collection * are equal to items in this collection * (same order, and same according to equals). public final boolean equals( Object other ) if( other == this ) return true; if(! ( other instanceof Collection ) ) Collection rhs = (Collection) other; if( size( )!= rhs.size( ) ) Iterator lhsitr = this.iterator( ); Iterator rhsitr = rhs.iterator( ); while( lhsitr.hasnext( ) ) if(!isequal( lhsitr.next( ), rhsitr.next( ) ) ) return true; -5

6 * Return the hashcode. public final int hashcode( ) int hashval = 1; Iterator itr = iterator( ); ); while( itr.hasnext( ) ) Object obj = itr.next( ); hashval = 31 * hashval + ( obj == null? 0 : obj.hashcode( ) return hashval; * Return true if two objects are equal; works * if objects can be null. private boolean isequal( Object lhs, Object rhs ) if( lhs == null ) return rhs == null; return lhs.equals( rhs ); -6

7 package weiss.util; public class extends implements List private static final int DEFAULT_CAPACITY = 10; private static final int NOT_FOUND = -1; private Object [ ] theitems; private int thesize; private int modcount = 0; * Construct an empty. public ( ) clear( ); * Construct an with same items as another Collection. public ( Collection other ) clear( ); Iterator itr = other.iterator( ); while( itr.hasnext( ) ) add( itr.next( ) ); -7

8 * Returns the number of items in this collection. public int size( ) return thesize; * Returns the item at position idx. idx the index to search in. ArrayIndexOutOfBoundsException if index is out of range. public Object get( int idx ) if( idx < 0 idx >= size( ) ) throw new ArrayIndexOutOfBoundsException( "Index " + idx + "; size " + size( ) ); return theitems[ idx ]; * Changes the item at position idx. public Object set( int idx, Object newval ) if( idx < 0 idx >= size( ) ) throw new ArrayIndexOutOfBoundsException( "Index " + idx + "; size " + size( ) ); Object old = theitems[ idx ]; theitems[ idx ] = newval; return old; * Tests if some item is in this collection. public boolean contains( Object x ) return findpos( x )!= NOT_FOUND; -8

9 * Returns the position of first item matching x in this collection, * or NOT_FOUND if not found. private int findpos( Object x ) for( int i = 0; i < size( ); i++ ) if( x == null ) if( theitems[ i ] == null ) return i; else if( x.equals( theitems[ i ] ) ) return i; return NOT_FOUND; * Adds an item to this collection, at the end. x any object. true. public boolean add( Object x ) if( theitems.length == size( ) ) Object [ ] old = theitems; theitems = new Object[ theitems.length * ]; for( int i = 0; i < size( ); i++ ) theitems[ i ] = old[ i ]; theitems[ thesize++ ] = x; modcount++; return true; -9

10 * Removes an item from this collection. public boolean remove( Object x ) int pos = findpos( x ); if( pos == NOT_FOUND ) else remove( pos ); return true; * Removes an item from this collection. public Object remove( int idx ) Object removeditem = theitems[ idx ]; for( int i = idx; i < size( ) - 1; i++ ) theitems[ i ] = theitems[ i + 1 ]; thesize--; modcount++; return removeditem; -10

11 * Change the size of this collection to zero. public void clear( ) thesize = 0; theitems = new Object[ DEFAULT_CAPACITY ]; modcount++; * Obtains an Iterator object used to traverse the collection. an iterator positioned prior to the first element. public Iterator iterator( ) return new Iterator( 0 ); * Obtains a ListIterator object used to traverse the collection bidirectionally. an iterator positioned prior to the requested element. idx the index to start the iterator. Use size() to do complete * reverse traversal. Use 0 to do complete forward traversal. IndexOutOfBoundsException if idx is not between 0 and size(), inclusive. public ListIterator listiterator( int idx ) return new Iterator( idx ); -11

12 Iterator * This is the implementation of the Iterator. * It maintains a notion of a current position and of * course the implicit reference to the. private class Iterator implements ListIterator private int current; private int expectedmodcount = modcount; private boolean nextcompleted = false; private boolean prevcompleted = false; Iterator( int pos ) if( pos < 0 pos > size( ) ) throw new IndexOutOfBoundsException( ); current = pos; Iterator public boolean hasnext( ) if( expectedmodcount!= modcount ) throw new ConcurrentModificationException( ); return current < size( ); public boolean hasprevious( ) if( expectedmodcount!= modcount ) throw new ConcurrentModificationException( ); return current > 0; public Object next( ) if(!hasnext( ) ) throw new NoSuchElementException( ); nextcompleted = true; prevcompleted = false; return theitems[ current++ ]; -12

13 Iterator public Object previous( ) if(!hasprevious( ) ) throw new NoSuchElementException( ); prevcompleted = true; nextcompleted = false; return theitems[ --current ]; public void remove( ) if( expectedmodcount!= modcount ) throw new ConcurrentModificationException( ); if( nextcompleted ).this.remove( --current ); else if( prevcompleted ).this.remove( current ); else throw new IllegalStateException( ); prevcompleted = nextcompleted = false; expectedmodcount++; -13