crunch-core/src/main/java/org/apache/crunch/materialize/MaterializableMap.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.crunch.materialize;

import java.util.AbstractMap;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

import org.apache.crunch.Pair;

public class MaterializableMap<K, V> extends AbstractMap<K, V> {

  private Iterable<Pair<K, V>> iterable;
  private Set<Map.Entry<K, V>> entrySet;

  public MaterializableMap(Iterable<Pair<K, V>> iterable) {
    this.iterable = iterable;
  }

  private Set<Map.Entry<K, V>> toMapEntries(Iterable<Pair<K, V>> xs) {
    HashMap<K, V> m = new HashMap<K, V>();
    for (Pair<K, V> x : xs)
      m.put(x.first(), x.second());
    return m.entrySet();
  }

  @Override
  public Set<Map.Entry<K, V>> entrySet() {
    if (entrySet == null)
      entrySet = toMapEntries(iterable);
    return entrySet;
  }

}