* * 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 Set * interface (for instance, the add method must not permit addition of * multiple instances of an object to a set).
* * Note that this class does not override any of the implementations from * the AbstractCollection class. It merely adds implementations * for equals and hashCode.
*
* This class is a member of the
*
* Java Collections Framework.
*
* @param
*
* This implementation first checks if the specified object is this
* set; if so it returns 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
* containsAll((Collection) o).
*
* @param o object to be compared for equality with this set
* @return 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 null element is defined to be zero.
* This ensures that s1.equals(s2) implies that
* s1.hashCode()==s2.hashCode() for any two sets s1
* and s2, as required by the general contract of
* {@link Object#hashCode}.
*
* This implementation iterates over the set, calling the
* 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 This implementation determines which is the smaller of this set
* and the specified collection, by invoking the 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 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 remove method.
*
* Note that this implementation will throw an
* UnsupportedOperationException if the iterator returned by the
* iterator method does not implement the remove method.
*
* @param c collection containing elements to be removed from this set
* @return true if this set changed as a result of the call
* @throws UnsupportedOperationException if the 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
* (optional)
* @throws NullPointerException if this set contains a null element and the
* specified collection does not permit null elements
* (optional),
* 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 (Iterator i = c.iterator(); i.hasNext(); )
modified |= remove(i.next());
} else {
for (Iterator i = iterator(); i.hasNext(); ) {
if (c.contains(i.next())) {
i.remove();
modified = true;
}
}
}
return modified;
}
}