KeyMap.java

/*
 * KeyMap.java May 2007
 *
 * Copyright (C) 2007, Niall Gallagher <niallg@users.sf.net>
 *
 * Licensed under the Apache 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.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 
 * implied. See the License for the specific language governing 
 * permissions and limitations under the License.
 */

package org.simpleframework.util;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Set;

/**
 * The <code>KeyMap</code> object is used to represent a map of values keyed
 * using a known string. This also ensures that the keys and the values added to
 * this hash map can be acquired in an independent list of values, ensuring that
 * modifications to the map do not have an impact on the lists provided, and
 * vice versa. The key map can also be used in a fore each look using the string
 * keys.
 * 
 * @author Niall Gallagher
 */
public class KeyMap<T> extends LinkedHashMap<String, T> implements
        Iterable<String> {

    /**
     * Constructor for the <code>KeyMap</code> object. This creates a hash map
     * that can expose the keys and values of the map as an independent
     * <code>List</code> containing the values. This can also be used within a
     * for loop for convenience.
     */
    public KeyMap() {
        super();
    }

    /**
     * This is used to produce an <code>Iterator</code> of values that can be
     * used to acquire the contents of the key map within a for each loop. The
     * key map can be modified while it is been iterated as the iterator is an
     * independent list of values.
     * 
     * @return this returns an iterator of the keys in the map
     */
    @Override
    public Iterator<String> iterator() {
        return this.getKeys().iterator();
    }

    /**
     * This is used to produce a <code>List</code> of the keys in the map. The
     * list produced is a copy of the internal keys and so can be modified and
     * used without affecting this map object.
     * 
     * @return this returns an independent list of the key values
     */
    public List<String> getKeys() {
        Set<String> keys = this.keySet();

        if (keys == null) return new ArrayList<String>();
        return new ArrayList<String>(keys);
    }

    /**
     * This is used to produce a <code>List</code> of the values in the map. The
     * list produced is a copy of the internal values and so can be modified and
     * used without affecting this map object.
     * 
     * @return this returns an independent list of the values
     */
    public List<T> getValues() {
        Collection<T> values = this.values();

        if (values == null) return new ArrayList<T>();
        return new ArrayList<T>(values);
    }
}