guava/src/com/google/common/collect/LexicographicalOrdering.java

/*
 * Copyright (C) 2007 The Guava Authors
 *
 * 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.google.common.collect;

import com.google.common.annotations.GwtCompatible;

import java.io.Serializable;
import java.util.Iterator;

import javax.annotation.Nullable;

/**
 * An ordering which sorts iterables by comparing corresponding elements
 * pairwise.
 */
@GwtCompatible(serializable = true)
final class LexicographicalOrdering<T>
    extends Ordering<Iterable<T>> implements Serializable {
  final Ordering<? super T> elementOrder;

  LexicographicalOrdering(Ordering<? super T> elementOrder) {
    this.elementOrder = elementOrder;
  }

  @Override public int compare(
      Iterable<T> leftIterable, Iterable<T> rightIterable) {
    Iterator<T> left = leftIterable.iterator();
    Iterator<T> right = rightIterable.iterator();
    while (left.hasNext()) {
      if (!right.hasNext()) {
        return LEFT_IS_GREATER; // because it's longer
      }
      int result = elementOrder.compare(left.next(), right.next());
      if (result != 0) {
        return result;
      }
    }
    if (right.hasNext()) {
      return RIGHT_IS_GREATER; // because it's longer
    }
    return 0;
  }

  @Override public boolean equals(@Nullable Object object) {
    if (object == this) {
      return true;
    }
    if (object instanceof LexicographicalOrdering) {
      LexicographicalOrdering<?> that = (LexicographicalOrdering<?>) object;
      return this.elementOrder.equals(that.elementOrder);
    }
    return false;
  }

  @Override public int hashCode() {
    return elementOrder.hashCode() ^ 2075626741; // meaningless
  }

  @Override public String toString() {
    return elementOrder + ".lexicographical()";
  }

  private static final long serialVersionUID = 0;
}