java.util.AbstractSet Maven / Gradle / Ivy
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* accompanied this code).
*
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*
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package java.util;
/**
* This class provides a skeletal implementation of the Set
* interface to minimize the effort required to implement this
* interface.
*
* 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 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 extends AbstractCollection implements Set {
/**
* Sole constructor. (For invocation by subclass constructors, typically
* implicit.)
*/
protected AbstractSet() {
}
// Comparison and hashing
/**
* Compares the specified object with this set for equality. Returns
* 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 equals method works
* properly across different implementations of the Set
* interface.
*
* 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 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 asymmetric set difference of
* the two sets.
*
* 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) {
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;
}
}