org.garret.consus
Class POCollection

java.lang.Object
  extended by org.garret.consus.Persistent
      extended by org.garret.consus.POCollection
All Implemented Interfaces:
java.util.Collection, java.lang.Iterable
Direct Known Subclasses:
POList

public abstract class POCollection
extends Persistent
implements java.util.Collection

This class provides a skeletion 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 methods.)

To implement a modifiable collection, the programmer must override the add method in this (which otherwise throws an UnsupportedOperationException), and the iterator returned by the iterator method must implement its own remove method.


Field Summary
 
Fields inherited from class org.garret.consus.Persistent
db, oid, PO_DELETED, PO_LOADED, PO_NEW, PO_STUB, state, type
 
Method Summary
 boolean add(java.lang.Object o)
          Ensures that this collection contains the specified element (optional operation).
 boolean addAll(java.util.Collection c)
          Adds all of the elements in the specified collection to this collection (optional operation).
 void clear()
          Removes all of the elements from this collection (optional operation).
 boolean contains(java.lang.Object o)
          Returns true if this collection contains the specified element.
 boolean containsAll(java.util.Collection c)
          Returns true if this collection contains all of the elements in the specified collection.
 boolean equals(java.lang.Object o)
          Compares the specified object with this list for equality.
 int hashCode()
          Returns the hash code value for this list.
 boolean isEmpty()
          Returns true if this collection contains no elements.
abstract  java.util.Iterator iterator()
          Returns an iterator of the elements contained in this collection.
 boolean remove(java.lang.Object o)
          Removes a single instance of the specified element from this collection, if it is present (optional operation).
 boolean removeAll(java.util.Collection c)
          Removes from this collection all of the elements that are contained in the specified collection (optional operation).
 boolean retainAll(java.util.Collection c)
          Retains only the elements in this collection that are contained in the specified collection (optional operation).
abstract  int size()
          Returns the number of elements in this collection.
 java.lang.Object[] toArray()
          Returns an array containing all of the elements in this collection.
 java.lang.Object[] toArray(java.lang.Object[] a)
          Returns an array with a runtime type of the specified array and that contains all of the elements in this collection.
 java.lang.String toString()
          Returns a string representation of this collection.
 
Methods inherited from class org.garret.consus.Persistent
assignOID, become, beginUpdate, endUpdate, get, get, getOid, getOid, getRef, getRef, isDeleted, isLoaded, isNew, load, loadClosure, loadComponents, lock, remove, save, store, store, unget
 
Methods inherited from class java.lang.Object
getClass, notify, notifyAll, wait, wait, wait
 

Method Detail

add

public boolean add(java.lang.Object o)
Ensures that this collection contains the specified element (optional operation). Returns true if the collection changed as a result of the call. (Returns false if this collection does not permit duplicates and already contains the specified element.) Collections that support this operation may place limitations on what elements can be added to the collection. In particular, some collections will refuse to add null elements, and others will impose restrictions on the type of elements that may be added. Collection classes should clearly specify in their documentation any restrictions on what elements can be added.

This implementation always throws an UnsupportedOperationException.

Specified by:
add in interface java.util.Collection
Parameters:
o - element whose presence in this collection is to be ensured.
Returns:
true if the collection changed as a result of the call.
Throws:
java.lang.UnsupportedOperationException - if the add method is not supported by this collection.
java.lang.NullPointerException - if this collection does not permit null elements, and the specified element is null.
java.lang.ClassCastException - if the class of the specified element prevents it from being added to this collection.
java.lang.IllegalArgumentException - if some aspect of this element prevents it from being added to this collection.

addAll

public boolean addAll(java.util.Collection c)
Adds all of the elements in the specified collection to this collection (optional operation). The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified collection is this collection, and this collection is non-empty.)

This implementation iterates through the specified collection, and adds each object returned by the iterator to this collection, in turn.

Note that this implementation will throw an UnsupportedOperationException unless add it is overridden.

Specified by:
addAll in interface java.util.Collection
Parameters:
c - collection whose elements are to be added to this collection.
Returns:
true if this collection changed as a result of the call.
Throws:
java.lang.UnsupportedOperationException - if the addAll method is not supported by this collection.
See Also:
add(Object)

clear

public void clear()
Removes all of the elements from this collection (optional operation). The collection will be empty after this call returns (unless it throws an exception).

This implementation iterates through the collection, removing each element using the Iterator.remove operation. Most implementations will probably choose to override this method for efficiency.

Note that this implementation will throw an UnsupportedOperationException if the iterator returned by this collection's iterator method does not implement the remove method.

Specified by:
clear in interface java.util.Collection
Throws:
java.lang.UnsupportedOperationException - if the remove method is not supported by this collection.

contains

public boolean contains(java.lang.Object o)
Returns true if this collection contains the specified element. It returns true if, and only if, this collection contains at least one element e such that (o==null ? e==null : o.equals(e)).

This implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element.

Specified by:
contains in interface java.util.Collection
Parameters:
o - object to be checked for existance in this collection.
Returns:
true if this collection contains the specified element.

containsAll

public boolean containsAll(java.util.Collection c)
Returns true if this collection contains all of the elements in the specified collection.

This implementation iterates over the specified collection, checking each element returned by the iterator in turn to see if it's contained in this collection. If all elements are found then true is returned, otherwise false.

Specified by:
containsAll in interface java.util.Collection
Parameters:
c - collection to be checked for containment in this collection.
Returns:
true if this collection contains all of the elements in the specified collection.
See Also:
contains(Object)

equals

public boolean equals(java.lang.Object o)
Compares the specified object with this list for equality. Returns true if and only if the specified object is a list, both lists have the same size, and all corresponding pairs of elements in the two lists are equal. (Two elements e1 and e2 are equal if (e1==null ? e2==null : e1.equals(e2)).) In other words, the two lists are defined as equal if they contain the same elements in the same order.

This implementation first checks that the specified object is in this list. If yes, it returns true; if not, it checks if the specified object is a list. If not, it returns false; if yes, it iterates through both lists, comparing corresponding pairs of elements. If any comparison returns false, this method returns false. If either iterator runs out of elements before the other, it returns false (as the lists are of unequal length). Otherwise it returns true when the iteration is completed.

Specified by:
equals in interface java.util.Collection
Overrides:
equals in class java.lang.Object
Parameters:
o - the object to be compared for equality with this list.
Returns:
true if the specified object is equal to this list.

hashCode

public int hashCode()
Returns the hash code value for this list.

This implementation uses the code that is used to define the list hash function in the documentation for the List.hashCode method.

Specified by:
hashCode in interface java.util.Collection
Overrides:
hashCode in class java.lang.Object
Returns:
the hash code value for this list.

isEmpty

public boolean isEmpty()
Returns true if this collection contains no elements.

This implementation returns size() == 0.

Specified by:
isEmpty in interface java.util.Collection
Returns:
true if this collection contains no elements.

iterator

public abstract java.util.Iterator iterator()
Returns an iterator of the elements contained in this collection.

Specified by:
iterator in interface java.util.Collection
Returns:
an iterator of the elements contained in this collection.

remove

public boolean remove(java.lang.Object o)
Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an element e such that (o==null ? e==null : o.equals(e)), if the collection contains one or more such elements. Returns true if the collection contained the specified element (or equivalently, if the collection changed as a result of the call).

This implementation iterates over the collection looking for the specified element. If it finds the element, it removes the element from the collection using the iterator's remove method.

Note that this implementation throws an UnsupportedOperationException if the iterator returned by this collection's iterator method does not implement the remove method.

Specified by:
remove in interface java.util.Collection
Parameters:
o - element to be removed from this collection, if present.
Returns:
true if the collection contained the specified element.
Throws:
java.lang.UnsupportedOperationException - if the remove method is not supported by this collection.

removeAll

public boolean removeAll(java.util.Collection c)
Removes from this collection all of the elements that are contained in the specified collection (optional operation).

This implementation iterates through this collection, checking each element returned by the iterator, to see if it exists in the specified collection. If it does exist, it is removed from this collection with the iterator's remove method.

Note that this implementation will throw an UnsupportedOperationException if the iterator returned by the iterator method does not implement the remove method.

Specified by:
removeAll in interface java.util.Collection
Parameters:
c - elements to be removed from this collection.
Returns:
true if this collection changed as a result of the call.
Throws:
java.lang.UnsupportedOperationException - removeAll is not supported by this collection.
See Also:
remove(Object), contains(Object)

retainAll

public boolean retainAll(java.util.Collection c)
Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, it removes from this collection all of the elements that do not exist in the specified collection.

This implementation iterates through this collection, checking each element, returned by the iterator, to see if it exists in the specified collection. If it does not exist, it is removed from this collection with the iterator's remove method.

Note that this implementation will throw an UnsupportedOperationException if the iterator returned by the iterator method does not implement the remove method.

Specified by:
retainAll in interface java.util.Collection
Returns:
true if this collection changed as a result of the call.
Throws:
java.lang.UnsupportedOperationException - if the retainAll method is not supported by this collection.
See Also:
remove(Object), contains(Object)

size

public abstract int size()
Returns the number of elements in this collection. If the collection contains more than Integer.MAX_VALUE elements it returns Integer.MAX_VALUE.

Specified by:
size in interface java.util.Collection
Returns:
the number of elements in this collection.

toArray

public java.lang.Object[] toArray()
Returns an array containing all of the elements in this collection. If the collection makes any guarantees as to the order its elements are returned by its iterator, this method must return the elements in the same order. The returned array will be "safe" in that no references to it are maintained by the collection. (In other words, this method must allocate a new array even if the collection is backed by an Array). The caller is thus free to modify the returned array.

This implementation allocates the array to be returned, and iterates over the elements in the collection, storing each object reference in the next consecutive element of the array, starting with element 0.

Specified by:
toArray in interface java.util.Collection
Returns:
an array containing all of the elements in this collection.

toArray

public java.lang.Object[] toArray(java.lang.Object[] a)
Returns an array with a runtime type of the specified array and that contains all of the elements in this collection. If the collection fits in the specified array, it is returned. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection.

If the collection fits in the specified array with room to spare (i.e. the array has more elements than the collection), the element in the array immediately following the end of the collection is set to null. This is useful in determining the length of the collection only if the caller knows that the collection does not contain any null elements.)

If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

This implementation checks if the array is large enough to contain the collection. If not, it allocates a new array of the correct size and type (using reflection). Then it iterates over the collection, storing each object reference in the next consecutive element of the array, starting with element 0. If the array is larger than the collection, a null is stored in the first location after the end of the collection.

Specified by:
toArray in interface java.util.Collection
Parameters:
a - the array into which the elements of the collection are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.
Returns:
an array containing the elements of the collection.
Throws:
java.lang.NullPointerException - if the specified array is null.
java.lang.ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this collection.

toString

public java.lang.String toString()
Returns a string representation of this collection. The string representation consists of a list of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings through String.valueOf(Object).

This implementation creates an empty string buffer, appends a left square bracket, and iterates through the collection appending the string representation of each element in turn. After appending each element, except the last, the string ", " is appended. Finally a right bracket is appended. A string is obtained from the string buffer and returned.

Overrides:
toString in class Persistent
Returns:
a string representation of this collection.