java.util.AbstractCollection Maven / Gradle / Ivy
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package java.util;
/**
* 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 collection being implemented admits a more efficient implementation.
*
* This class is a member of the
*
* Java Collections Framework.
*
* @author Josh Bloch
* @author Neal Gafter
* @see Collection
* @since 1.2
*/
public abstract class AbstractCollection implements Collection {
/**
* Sole constructor. (For invocation by subclass constructors, typically
* implicit.)
*/
protected AbstractCollection() {
}
// Query Operations
/**
* Returns an iterator over the elements contained in this collection.
*
* @return an iterator over the elements contained in this collection
*/
public abstract Iterator iterator();
public abstract int size();
/**
* {@inheritDoc}
*
* This implementation returns size() == 0.
*/
public boolean isEmpty() {
return size() == 0;
}
/**
* {@inheritDoc}
*
*
This implementation iterates over the elements in the collection,
* checking each element in turn for equality with the specified element.
*
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*/
public boolean contains(Object o) {
Iterator it = iterator();
if (o==null) {
while (it.hasNext())
if (it.next()==null)
return true;
} else {
while (it.hasNext())
if (o.equals(it.next()))
return true;
}
return false;
}
/**
* {@inheritDoc}
*
* This implementation returns an array containing all the elements
* returned by this collection's iterator, in the same order, stored in
* consecutive elements of the array, starting with index {@code 0}.
* The length of the returned array is equal to the number of elements
* returned by the iterator, even if the size of this collection changes
* during iteration, as might happen if the collection permits
* concurrent modification during iteration. The {@code size} method is
* called only as an optimization hint; the correct result is returned
* even if the iterator returns a different number of elements.
*
*
This method is equivalent to:
*
*
{@code
* List list = new ArrayList(size());
* for (E e : this)
* list.add(e);
* return list.toArray();
* }
*/
public Object[] toArray() {
// Estimate size of array; be prepared to see more or fewer elements
Object[] r = new Object[size()];
Iterator it = iterator();
for (int i = 0; i < r.length; i++) {
if (! it.hasNext()) // fewer elements than expected
return Arrays.copyOf(r, i);
r[i] = it.next();
}
return it.hasNext() ? finishToArray(r, it) : r;
}
/**
* {@inheritDoc}
*
* This implementation returns an array containing all the elements
* returned by this collection's iterator in the same order, stored in
* consecutive elements of the array, starting with index {@code 0}.
* If the number of elements returned by the iterator is too large to
* fit into the specified array, then the elements are returned in a
* newly allocated array with length equal to the number of elements
* returned by the iterator, even if the size of this collection
* changes during iteration, as might happen if the collection permits
* concurrent modification during iteration. The {@code size} method is
* called only as an optimization hint; the correct result is returned
* even if the iterator returns a different number of elements.
*
*
This method is equivalent to:
*
*
{@code
* List list = new ArrayList(size());
* for (E e : this)
* list.add(e);
* return list.toArray(a);
* }
*
* @throws ArrayStoreException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*/
public T[] toArray(T[] a) {
// Estimate size of array; be prepared to see more or fewer elements
int size = size();
T[] r = a.length >= size ? a :
(T[])java.lang.reflect.Array
.newInstance(a.getClass().getComponentType(), size);
Iterator it = iterator();
for (int i = 0; i < r.length; i++) {
if (! it.hasNext()) { // fewer elements than expected
if (a != r)
return Arrays.copyOf(r, i);
r[i] = null; // null-terminate
return r;
}
r[i] = (T)it.next();
}
return it.hasNext() ? finishToArray(r, it) : r;
}
/**
* The maximum size of array to allocate.
* Some VMs reserve some header words in an array.
* Attempts to allocate larger arrays may result in
* OutOfMemoryError: Requested array size exceeds VM limit
*/
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/**
* Reallocates the array being used within toArray when the iterator
* returned more elements than expected, and finishes filling it from
* the iterator.
*
* @param r the array, replete with previously stored elements
* @param it the in-progress iterator over this collection
* @return array containing the elements in the given array, plus any
* further elements returned by the iterator, trimmed to size
*/
private static T[] finishToArray(T[] r, Iterator it) {
int i = r.length;
while (it.hasNext()) {
int cap = r.length;
if (i == cap) {
int newCap = cap + (cap >> 1) + 1;
// overflow-conscious code
if (newCap - MAX_ARRAY_SIZE > 0)
newCap = hugeCapacity(cap + 1);
r = Arrays.copyOf(r, newCap);
}
r[i++] = (T)it.next();
}
// trim if overallocated
return (i == r.length) ? r : Arrays.copyOf(r, i);
}
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError
("Required array size too large");
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}
// Modification Operations
/**
* {@inheritDoc}
*
* This implementation always throws an
* UnsupportedOperationException.
*
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
* @throws IllegalStateException {@inheritDoc}
*/
public boolean add(E e) {
throw new UnsupportedOperationException();
}
/**
* {@inheritDoc}
*
*
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 and this collection contains the specified object.
*
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*/
public boolean remove(Object o) {
Iterator it = iterator();
if (o==null) {
while (it.hasNext()) {
if (it.next()==null) {
it.remove();
return true;
}
}
} else {
while (it.hasNext()) {
if (o.equals(it.next())) {
it.remove();
return true;
}
}
}
return false;
}
// Bulk Operations
/**
* {@inheritDoc}
*
* 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 so
* contained true is returned, otherwise false.
*
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @see #contains(Object)
*/
public boolean containsAll(Collection c) {
for (Object e : c)
if (!contains(e))
return false;
return true;
}
/**
* {@inheritDoc}
*
*
This implementation iterates over 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 is
* overridden (assuming the specified collection is non-empty).
*
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
* @throws IllegalStateException {@inheritDoc}
*
* @see #add(Object)
*/
public boolean addAll(Collection c) {
boolean modified = false;
for (E e : c)
if (add(e))
modified = true;
return modified;
}
/**
* {@inheritDoc}
*
*
This implementation iterates over this collection, checking each
* element returned by the iterator in turn to see if it's contained
* in the specified collection. If it's so contained, it's 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
* and this collection contains one or more elements in common with the
* specified collection.
*
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*
* @see #remove(Object)
* @see #contains(Object)
*/
public boolean removeAll(Collection c) {
boolean modified = false;
Iterator it = iterator();
while (it.hasNext()) {
if (c.contains(it.next())) {
it.remove();
modified = true;
}
}
return modified;
}
/**
* {@inheritDoc}
*
*
This implementation iterates over this collection, checking each
* element returned by the iterator in turn to see if it's contained
* in the specified collection. If it's not so contained, it's 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
* and this collection contains one or more elements not present in the
* specified collection.
*
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*
* @see #remove(Object)
* @see #contains(Object)
*/
public boolean retainAll(Collection c) {
boolean modified = false;
Iterator it = iterator();
while (it.hasNext()) {
if (!c.contains(it.next())) {
it.remove();
modified = true;
}
}
return modified;
}
/**
* {@inheritDoc}
*
* This implementation iterates over this 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 and this collection is non-empty.
*
* @throws UnsupportedOperationException {@inheritDoc}
*/
public void clear() {
Iterator it = iterator();
while (it.hasNext()) {
it.next();
it.remove();
}
}
// String conversion
/**
* 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 as
* by {@link String#valueOf(Object)}.
*
* @return a string representation of this collection
*/
public String toString() {
Iterator it = iterator();
if (! it.hasNext())
return "[]";
StringBuilder sb = new StringBuilder();
sb.append('[');
for (;;) {
E e = it.next();
sb.append(e == this ? "(this Collection)" : e);
if (! it.hasNext())
return sb.append(']').toString();
sb.append(',').append(' ');
}
}
}