OrderRetainingMap.java

/*
 * Copyright 1999-2012 Alibaba Group.
 * 
 * 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 fm.liu.timo.config.util;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Set;

public class OrderRetainingMap<K, V> extends HashMap<K, V> {
    private static final long serialVersionUID = 1L;

    private Set<K>  keyOrder   = new ArraySet<K>();
    private List<V> valueOrder = new ArrayList<V>();

    @Override
    public V put(K key, V value) {
        keyOrder.add(key);
        valueOrder.add(value);
        return super.put(key, value);
    }

    @Override
    public Collection<V> values() {
        return Collections.unmodifiableList(valueOrder);
    }

    @Override
    public Set<K> keySet() {
        return Collections.unmodifiableSet(keyOrder);
    }

    @Override
    public Set<Entry<K, V>> entrySet() {
        throw new UnsupportedOperationException();
    }

    private static class ArraySet<T> extends ArrayList<T>implements Set<T> {

        private static final long serialVersionUID = 1L;
    }

}