ListMap.java

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// Copyright 2014 Cloudera Inc.
//
// 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 com.cloudera.impala.util;

import java.util.Map;
import java.util.ArrayList;
import java.util.List;

import com.google.common.base.Preconditions;
import com.google.common.collect.Maps;
import com.google.common.collect.Lists;

public class ListMap<T> {
  // Maps from Integer to T.
  private List<T> list_ = Lists.newArrayList();
  // Maps from T to Integer.
  private final Map<T, Integer> map_ = Maps.newHashMap();

  public List<T> getList() { return list_; }
  public int size() { return list_.size(); }

  public T getEntry(Integer index) { return list_.get(index); }

  public Integer getIndex(T t) {
    Integer index = map_.get(t);
    if (index == null) {
      // No match was found, add a new entry.
      list_.add(t);
      index = list_.size() - 1;
      map_.put(t, index);
    }
    return index;
  }

  public void populate(List<T> list) {
    Preconditions.checkState(list_.isEmpty() && map_.isEmpty());
    // Require list to be an ArrayList so that getEntry() is fast.
    Preconditions.checkState(list instanceof ArrayList<?>);
    list_ = list;
    for (int i = 0; i < list_.size(); ++i) {
      map_.put(list_.get(i), i);
    }
  }
}