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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
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* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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*/
package java.util;
/**
* This class provides a skeletal implementation of the {@code Set}
* interface to minimize the effort required to implement this
* interface. <p>
*
* The process of implementing a set by extending this class is identical
* to that of implementing a Collection by extending AbstractCollection,
* except that all of the methods and constructors in subclasses of this
* class must obey the additional constraints imposed by the {@code Set}
* interface (for instance, the add method must not permit addition of
* multiple instances of an object to a set).<p>
*
* Note that this class does not override any of the implementations from
* the {@code AbstractCollection} class. It merely adds implementations
* for {@code equals} and {@code hashCode}.<p>
*
* This class is a member of the
* <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @param <E> the type of elements maintained by this set
*
* @author Josh Bloch
* @author Neal Gafter
* @see Collection
* @see AbstractCollection
* @see Set
* @since 1.2
*/
public abstract class AbstractSet<E> extends AbstractCollection<E> implements Set<E> {
/**
* Sole constructor. (For invocation by subclass constructors, typically
* implicit.)
*/
protected AbstractSet() {
}
// Comparison and hashing
/**
* Compares the specified object with this set for equality. Returns
* {@code true} if the given object is also a set, the two sets have
* the same size, and every member of the given set is contained in
* this set. This ensures that the {@code equals} method works
* properly across different implementations of the {@code Set}
* interface.<p>
*
* This implementation first checks if the specified object is this
* set; if so it returns {@code true}. Then, it checks if the
* specified object is a set whose size is identical to the size of
* this set; if not, it returns false. If so, it returns
* {@code containsAll((Collection) o)}.
*
* @param o object to be compared for equality with this set
* @return {@code true} if the specified object is equal to this set
*/
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Set))
return false;
Collection<?> c = (Collection<?>) o;
if (c.size() != size())
return false;
try {
return containsAll(c);
} catch (ClassCastException unused) {
return false;
} catch (NullPointerException unused) {
return false;
}
}
/**
* Returns the hash code value for this set. The hash code of a set is
* defined to be the sum of the hash codes of the elements in the set,
* where the hash code of a {@code null} element is defined to be zero.
* This ensures that {@code s1.equals(s2)} implies that
* {@code s1.hashCode()==s2.hashCode()} for any two sets {@code s1}
* and {@code s2}, as required by the general contract of
* {@link Object#hashCode}.
*
* <p>This implementation iterates over the set, calling the
* {@code hashCode} method on each element in the set, and adding up
* the results.
*
* @return the hash code value for this set
* @see Object#equals(Object)
* @see Set#equals(Object)
*/
public int hashCode() {
int h = 0;
Iterator<E> i = iterator();
while (i.hasNext()) {
E obj = i.next();
if (obj != null)
h += obj.hashCode();
}
return h;
}
/**
* Removes from this set all of its elements that are contained in the
* specified collection (optional operation). If the specified
* collection is also a set, this operation effectively modifies this
* set so that its value is the <i>asymmetric set difference</i> of
* the two sets.
*
* <p>This implementation determines which is the smaller of this set
* and the specified collection, by invoking the {@code size}
* method on each. If this set has fewer elements, then the
* implementation iterates over this set, checking each element
* returned by the iterator in turn to see if it is contained in
* the specified collection. If it is so contained, it is removed
* from this set with the iterator's {@code remove} method. If
* the specified collection has fewer elements, then the
* implementation iterates over the specified collection, removing
* from this set each element returned by the iterator, using this
* set's {@code remove} method.
*
* <p>Note that this implementation will throw an
* {@code UnsupportedOperationException} if the iterator returned by the
* {@code iterator} method does not implement the {@code remove} method.
*
* @param c collection containing elements to be removed from this set
* @return {@code true} if this set changed as a result of the call
* @throws UnsupportedOperationException if the {@code removeAll} operation
* is not supported by this set
* @throws ClassCastException if the class of an element of this set
* is incompatible with the specified collection
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if this set contains a null element and the
* specified collection does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see #remove(Object)
* @see #contains(Object)
*/
public boolean removeAll(Collection<?> c) {
Objects.requireNonNull(c);
boolean modified = false;
if (size() > c.size()) {
for (Object e : c)
modified |= remove(e);
} else {
for (Iterator<?> i = iterator(); i.hasNext(); ) {
if (c.contains(i.next())) {
i.remove();
modified = true;
}
}
}
return modified;
}
}