abstractmap.java

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/*
 * @(#)AbstractMap.java	1.34 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.util;
import java.util.Map.Entry;

/**
 * This class provides a skeletal implementation of the <tt>Map</tt>
 * interface, to minimize the effort required to implement this interface. <p>
 *
 * To implement an unmodifiable map, the programmer needs only to extend this
 * class and provide an implementation for the <tt>entrySet</tt> method, which
 * returns a set-view of the map's mappings.  Typically, the returned set
 * will, in turn, be implemented atop <tt>AbstractSet</tt>.  This set should
 * not support the <tt>add</tt> or <tt>remove</tt> methods, and its iterator
 * should not support the <tt>remove</tt> method.<p>
 *
 * To implement a modifiable map, the programmer must additionally override
 * this class's <tt>put</tt> method (which otherwise throws an
 * <tt>UnsupportedOperationException</tt>), and the iterator returned by
 * <tt>entrySet().iterator()</tt> must additionally implement its
 * <tt>remove</tt> method.<p>
 *
 * The programmer should generally provide a void (no argument) and map
 * constructor, as per the recommendation in the <tt>Map</tt> interface
 * specification.<p>
 *
 * The documentation for each non-abstract methods in this class describes its
 * implementation in detail.  Each of these methods may be overridden if the
 * map being implemented admits a more efficient implementation.<p>
 *
 * This class is a member of the 
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @author  Josh Bloch
 * @version 1.34, 01/23/03
 * @see Map
 * @see Collection
 * @since 1.2
 */

public abstract class AbstractMap implements Map {
    /**
     * Sole constructor.  (For invocation by subclass constructors, typically
     * implicit.)
     */
    protected AbstractMap() {
    }

    // Query Operations

    /**
     * Returns the number of key-value mappings in this map.  If the map
     * contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
     * <tt>Integer.MAX_VALUE</tt>.<p>
     *
     * This implementation returns <tt>entrySet().size()</tt>.
     *
     * @return the number of key-value mappings in this map.
     */
    public int size() {
	return entrySet().size();
    }

    /**
     * Returns <tt>true</tt> if this map contains no key-value mappings. <p>
     *
     * This implementation returns <tt>size() == 0</tt>.
     *
     * @return <tt>true</tt> if this map contains no key-value mappings.
     */
    public boolean isEmpty() {
	return size() == 0;
    }

    /**
     * Returns <tt>true</tt> if this map maps one or more keys to this value.
     * More formally, returns <tt>true</tt> if and only if this map contains
     * at least one mapping to a value <tt>v</tt> such that <tt>(value==null ?
     * v==null : value.equals(v))</tt>.  This operation will probably require
     * time linear in the map size for most implementations of map.<p>
     *
     * This implementation iterates over entrySet() searching for an entry
     * with the specified value.  If such an entry is found, <tt>true</tt> is
     * returned.  If the iteration terminates without finding such an entry,
     * <tt>false</tt> is returned.  Note that this implementation requires
     * linear time in the size of the map.
     *
     * @param value value whose presence in this map is to be tested.
     * 
     * @return <tt>true</tt> if this map maps one or more keys to this value.
     */
    public boolean containsValue(Object value) {
	Iterator i = entrySet().iterator();
	if (value==null) {
	    while (i.hasNext()) {
		Entry e = (Entry) i.next();
		if (e.getValue()==null)
		    return true;
	    }
	} else {
	    while (i.hasNext()) {
		Entry e = (Entry) i.next();
		if (value.equals(e.getValue()))
		    return true;
	    }
	}
	return false;
    }

    /**
     * Returns <tt>true</tt> if this map contains a mapping for the specified
     * key. <p>
     *
     * This implementation iterates over <tt>entrySet()</tt> searching for an
     * entry with the specified key.  If such an entry is found, <tt>true</tt>
     * is returned.  If the iteration terminates without finding such an
     * entry, <tt>false</tt> is returned.  Note that this implementation
     * requires linear time in the size of the map; many implementations will
     * override this method.
     *
     * @param key key whose presence in this map is to be tested.
     * @return <tt>true</tt> if this map contains a mapping for the specified
     *            key.
     * 
     * @throws NullPointerException key is <tt>null</tt> and this map does not
     *            not permit <tt>null</tt> keys.
     */
    public boolean containsKey(Object key) {
	Iterator i = entrySet().iterator();
	if (key==null) {
	    while (i.hasNext()) {
		Entry e = (Entry) i.next();
		if (e.getKey()==null)
		    return true;
	    }
	} else {
	    while (i.hasNext()) {
		Entry e = (Entry) i.next();
		if (key.equals(e.getKey()))
		    return true;
	    }
	}
	return false;
    }

    /**
     * Returns the value to which this map maps the specified key.  Returns
     * <tt>null</tt> if the map contains no mapping for this key.  A return
     * value of <tt>null</tt> does not <i>necessarily</i> indicate that the
     * map contains no mapping for the key; it's also possible that the map
     * explicitly maps the key to <tt>null</tt>.  The containsKey operation
     * may be used to distinguish these two cases. <p>
     *
     * This implementation iterates over <tt>entrySet()</tt> searching for an
     * entry with the specified key.  If such an entry is found, the entry's
     * value is returned.  If the iteration terminates without finding such an
     * entry, <tt>null</tt> is returned.  Note that this implementation
     * requires linear time in the size of the map; many implementations will
     * override this method.
     *
     * @param key key whose associated value is to be returned.
     * @return the value to which this map maps the specified key.
     * 
     * @throws NullPointerException if the key is <tt>null</tt> and this map
     *		  does not not permit <tt>null</tt> keys.
     * 
     * @see #containsKey(Object)
     */
    public Object get(Object key) {
	Iterator i = entrySet().iterator();
	if (key==null) {
	    while (i.hasNext()) {
		Entry e = (Entry) i.next();
		if (e.getKey()==null)
		    return e.getValue();
	    }
	} else {
	    while (i.hasNext()) {
		Entry e = (Entry) i.next();
		if (key.equals(e.getKey()))
		    return e.getValue();
	    }
	}
	return null;
    }


    // Modification Operations

    /**
     * Associates the specified value with the specified key in this map
     * (optional operation).  If the map previously contained a mapping for
     * this key, the old value is replaced.<p>
     *
     * This implementation always throws an
     * <tt>UnsupportedOperationException</tt>.
     *
     * @param key key with which the specified value is to be associated.
     * @param value value to be associated with the specified key.
     * 
     * @return previous value associated with specified key, or <tt>null</tt>
     *	       if there was no mapping for key.  (A <tt>null</tt> return can
     *	       also indicate that the map previously associated <tt>null</tt>
     *	       with the specified key, if the implementation supports
     *	       <tt>null</tt> values.)
     * 
     * @throws UnsupportedOperationException if the <tt>put</tt> operation is
     *	          not supported by this map.
     * 
     * @throws ClassCastException if the class of the specified key or value
     * 	          prevents it from being stored in this map.
     * 
     * @throws IllegalArgumentException if some aspect of this key or value *
     *            prevents it from being stored in this map.
     * 
     * @throws NullPointerException this map does not permit <tt>null</tt>
     *            keys or values, and the specified key or value is
     *            <tt>null</tt>.
     */
    public Object put(Object key, Object value) {
	throw new UnsupportedOperationException();
    }

    /**
     * Removes the mapping for this key from this map if present (optional
     * operation). <p>
     *
     * This implementation iterates over <tt>entrySet()</tt> searching for an
     * entry with the specified key.  If such an entry is found, its value is
     * obtained with its <tt>getValue</tt> operation, the entry is is removed
     * from the Collection (and the backing map) with the iterator's
     * <tt>remove</tt> operation, and the saved value is returned.  If the
     * iteration terminates without finding such an entry, <tt>null</tt> is
     * returned.  Note that this implementation requires linear time in the
     * size of the map; many implementations will override this method.<p>
     *
     * Note that this implementation throws an
     * <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt> iterator
     * does not support the <tt>remove</tt> method and this map contains a
     * mapping for the specified key.
     *
     * @param key key whose mapping is to be removed from the map.
     * @return previous value associated with specified key, or <tt>null</tt>
     *	       if there was no entry for key.  (A <tt>null</tt> return can
     *	       also indicate that the map previously associated <tt>null</tt>
     *	       with the specified key, if the implementation supports
     *	       <tt>null</tt> values.)
     * @throws UnsupportedOperationException if the <tt>remove</tt> operation
     * 		  is not supported by this map.
     */
    public Object remove(Object key) {
	Iterator i = entrySet().iterator();
	Entry correctEntry = null;
	if (key==null) {
	    while (correctEntry==null && i.hasNext()) {
		Entry e = (Entry) i.next();
		if (e.getKey()==null)
		    correctEntry = e;
	    }
	} else {
	    while (correctEntry==null && i.hasNext()) {
		Entry e = (Entry) i.next();
		if (key.equals(e.getKey()))
		    correctEntry = e;
	    }
	}

	Object oldValue = null;
	if (correctEntry !=null) {
	    oldValue = correctEntry.getValue();
	    i.remove();
	}
	return oldValue;
    }


    // Bulk Operations

    /**
     * Copies all of the mappings from the specified map to this map
     * (optional operation).  These mappings will replace any mappings that
     * this map had for any of the keys currently in the specified map.<p>
     *
     * This implementation iterates over the specified map's
     * <tt>entrySet()</tt> collection, and calls this map's <tt>put</tt>
     * operation once for each entry returned by the iteration.<p>
     *
     * Note that this implementation throws an
     * <tt>UnsupportedOperationException</tt> if this map does not support
     * the <tt>put</tt> operation and the specified map is nonempty.
     *
     * @param t mappings to be stored in this map.
     * 
     * @throws UnsupportedOperationException if the <tt>putAll</tt> operation
     * 		  is not supported by this map.
     * 
     * @throws ClassCastException if the class of a key or value in the
     * 	          specified map prevents it from being stored in this map.
     * 
     * @throws IllegalArgumentException if some aspect of a key or value in
     *	          the specified map prevents it from being stored in this map.
     * @throws NullPointerException the specified map is <tt>null</tt>, or if
     *         this map does not permit <tt>null</tt> keys or values, and the
     *         specified map contains <tt>null</tt> keys or values.
     */
    public void putAll(Map t) {
	Iterator i = t.entrySet().iterator();
	while (i.hasNext()) {
	    Entry e = (Entry) i.next();
	    put(e.getKey(), e.getValue());
	}
    }

    /**
     * Removes all mappings from this map (optional operation). <p>
     *
     * This implementation calls <tt>entrySet().clear()</tt>.
     *
     * Note that this implementation throws an
     * <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt>
     * does not support the <tt>clear</tt> operation.
     *
     * @throws    UnsupportedOperationException clear is not supported
     * 		  by this map.
     */
    public void clear() {
	entrySet().clear();
    }