BEGIN LICENSE BLOCK *****
Version: EPL 2.0/GPL 2.0/LGPL 2.1
The contents of this file are subject to the Eclipse Public
License Version 2.0 (the "License"); you may not use this file
except in compliance with the License. You may obtain a copy of
the License at http://www.eclipse.org/legal/epl-v20.html
Software distributed under the License is distributed on an "AS
IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
implied. See the License for the specific language governing
rights and limitations under the License.
Copyright (C) 2006 Kresten Krab Thorup 
Alternatively, the contents of this file may be used under the terms of
either of the GNU General Public License Version 2 or later (the "GPL"),
or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
in which case the provisions of the GPL or the LGPL are applicable instead
of those above. If you wish to allow use of your version of this file only
under the terms of either the GPL or the LGPL, and not to allow others to
use your version of this file under the terms of the EPL, indicate your
decision by deleting the provisions above and replace them with the notice
and other provisions required by the GPL or the LGPL. If you do not delete
the provisions above, a recipient may use your version of this file under
the terms of any one of the EPL, the GPL or the LGPL.
END LICENSE BLOCK /***** BEGIN LICENSE BLOCK *****
 * Version: EPL 2.0/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Eclipse Public
 * License Version 2.0 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.eclipse.org/legal/epl-v20.html
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * Copyright (C) 2006 Kresten Krab Thorup <krab@gnu.org>
 * 
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the EPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the EPL, the GPL or the LGPL.
 ***** END LICENSE BLOCK *****/

package org.jruby.util;

import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

A GenericMap is simply an abstract java.util.Map 
implementation for which subclasses really only need to implement 
the method entryIterator. 
Author:
Kresten Krab Thorup (krab@trifork.com)/**
 * A <code>GenericMap</code> is simply an abstract <code>java.util.Map</code> 
 * implementation for which subclasses really only need to implement 
 * the method entryIterator. 
 * 
 * @author Kresten Krab Thorup (krab@trifork.com)
 */

public abstract class GenericMap implements Map {
    protected int size;

    public int size() {
        return size;
    }

    public boolean isEmpty() {
        return size() == 0;
    }

    protected int keyHash(Object key) {
        return key == null ? 0 : key.hashCode();
    }

    protected boolean keyEquals(Object containedKey, Object givenKey) {
        return containedKey == null ? givenKey == null : containedKey.equals(givenKey);
    }

    protected int valueHash(Object value) {
        return value == null ? 0 : value.hashCode();
    }

    protected boolean valueEquals(Object value1, Object value2) {
        return value1 == null ? value2 == null : value1.equals(value2);
    }

    abstract class Entry implements Map.Entry {
        @Override
        public int hashCode() {
            return keyHash(getKey()) ^ valueHash(getValue());
        }

        @Override
        public boolean equals(Object other) {
            if (other instanceof Map.Entry) {
                Map.Entry ent = (Map.Entry) other;
                return keyEquals(getKey(), ent.getKey()) && valueEquals(getValue(), ent.getValue());
            } 

            return false;
        }
    }

    public void putAll(Map other) {
        if (other == this) return;

        for (Iterator it = other.entrySet().iterator(); it.hasNext();) {
            Map.Entry entry = (Map.Entry) it.next();
            
            put(entry.getKey(), entry.getValue());
        }
    }

    protected abstract Iterator entryIterator();

    protected Iterator keyIterator() {
        return new KeyIterator();
    }

    protected Iterator valueIterator() {
        return new ValueIterator();
    }

    abstract class KeyOrValueIterator implements Iterator {
        Iterator iter = entryIterator();

        public boolean hasNext() {
            return iter.hasNext();
        }

        protected Map.Entry nextEntry() {
            return (Map.Entry) iter.next();
        }

        public void remove() {
            throw new UnsupportedOperationException();
        }
    }

    class KeyIterator extends KeyOrValueIterator {
        public Object next() {
            return nextEntry().getKey();
        }
    }

    class ValueIterator extends KeyOrValueIterator {
        public Object next() {
            return nextEntry().getValue();
        }
    }

    
I don't quite understand why we need to replace this method from
AbstractCollection, but it has been observed that toArray returns the
 *reverse* order of elements. --Kresten
/**
     * I don't quite understand why we need to replace this method from
     * AbstractCollection, but it has been observed that toArray returns the
     * *reverse* order of elements. --Kresten
     */
    private static Object[] toArray(Object[] arr, int size, Iterator it) {
        Object[] out;

        if (arr != null && arr.length >= size) {
            out = arr;
        } else if (arr == null) {
            out = new Object[size];
        } else {
            out = (Object[]) java.lang.reflect.Array.newInstance(arr.getClass().getComponentType(), size);
        }

        for (int i = 0; i < size; i++) {
            out[i] = it.next();
        }

        if (out.length > size) out[size] = null;

        return out;
    }

    public Collection values() {
        return new AbstractCollection() {
            public Iterator iterator() {
                return valueIterator();
            }

            public int size() {
                return GenericMap.this.size();
            }

            @Override
            public Object[] toArray(Object[] arr) {
                return GenericMap.toArray(arr, size(), iterator());
            }
        };
    }

    public Set keySet() {
        return new AbstractSet() {
            public Iterator iterator() {
                return keyIterator();
            }

            public int size() {
                return GenericMap.this.size();
            }

            @Override
            public Object[] toArray(Object[] arr) {
                return GenericMap.toArray(arr, size(), iterator());
            }
        };
    }

    @Override
    public int hashCode() {
        int code = 0;
        
        for (Iterator it = entryIterator(); it.hasNext(); ) {
            code += it.next().hashCode();
        }

        return code;
    }

    @Override
    public boolean equals(Object other) {
        if (!(other instanceof Map)) return false;

        Map map = (Map) other;

        if (map.size() != size()) return false;
            
        for (Iterator it = entryIterator(); it.hasNext();) {
            Entry ent = (Entry) it.next();
            Object key = ent.getKey();
            Object val = ent.getValue();

            if (map.containsKey(key)) {
                Object otherVal = map.get(key);
                if (!valueEquals(val, otherVal)) return false;
            }
        }
            
        return true;
    }

    public Set entrySet() {
        return new AbstractSet() {
            public Iterator iterator() {
                return entryIterator();
            }

            public int size() {
                return size;
            }

            @Override
            public Object[] toArray(Object[] arr) {
                return GenericMap.toArray(arr, size(), iterator());
            }
        };
    }

    
return the element with the given key /** return the element with the given key */
    public boolean containsValue(Object value) {
        for (Iterator it = valueIterator(); it.hasNext(); ) {
            if (valueEquals(value, it.next())) return true;
        }
        
        return false;
    }

    public boolean containsKey(Object key) {
        return get(key) != null;
    }
}