java.util: abstract public class: AbstractSet

java.util
abstract public class: AbstractSet [javadoc | source]

java.lang.Object
   java.util.AbstractCollection<E>
      java.util.AbstractSet

All Implemented Interfaces:
Set, Collection

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.

Parameters:

- the type of elements maintained by this set

Also see:

Collection

AbstractCollection

Set

author: Josh - Bloch

author: Neal - Gafter

since: 1.2 -

Constructor:
protected AbstractSet() { } Sole constructor. (For invocation by subclass constructors, typically implicit.)

Constructor:

 protected AbstractSet() {

}

Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method from java.util.AbstractSet Summary:
equals, hashCode, removeAll

Methods from java.util.AbstractCollection:
add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray, toString

Methods from java.lang.Object:
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method from java.util.AbstractSet Detail:
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; } } 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)`.
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; } 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 Object#hashCode . This implementation iterates over the set, calling the `hashCode` method on each element in the set, and adding up the results.
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; } 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.

Method from java.util.AbstractSet Detail:

 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;
        }
}

true

equals

Set

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).

 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;
}

null

s1.equals(s2)

s1.hashCode()==s2.hashCode()

s1

s2

Object#hashCode

This implementation iterates over the set, calling the hashCode method on each element in the set, and adding up the results.

 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;
}

asymmetric set difference

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.