com.b2international.commons.ExplicitFirstOrdering.java Source code

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Here is the source code for com.b2international.commons.ExplicitFirstOrdering.java

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/*
 * Copyright (C) 2007 Google 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.b2international.commons;

import java.io.Serializable;
import java.util.List;

import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Lists;
import com.google.common.collect.Ordering;

/**
 * An ordering that compares objects according to a given order. If a compared
 * object is not among the given elements, it will be placed last in the order.
 * 
 */
public class ExplicitFirstOrdering<T> extends Ordering<T> implements Serializable {

    private static final long serialVersionUID = 0;

    public static <T> ExplicitFirstOrdering<T> create(T firstValue, T... nextValues) {
        return new ExplicitFirstOrdering<T>(Lists.asList(firstValue, nextValues));
    }

    public static <T> ExplicitFirstOrdering<T> create(List<T> valuesInOrder) {
        return new ExplicitFirstOrdering<T>(valuesInOrder);
    }

    private final ImmutableMap<T, Integer> rankMap;
    private final int maxRank;

    private ExplicitFirstOrdering(List<T> valuesInOrder) {

        ImmutableMap.Builder<T, Integer> builder = ImmutableMap.builder();
        int rank = 0;

        for (T value : valuesInOrder) {
            builder.put(value, rank++);
        }

        this.rankMap = builder.build();
        this.maxRank = rank;
    }

    public int compare(T left, T right) {
        return rank(left) - rank(right); // safe because both are nonnegative
    }

    private int rank(T value) {
        Integer rank = rankMap.get(value);
        return (rank == null) ? maxRank : rank;
    }

    @Override
    public boolean equals(Object object) {

        if (object instanceof ExplicitFirstOrdering<?>) {
            ExplicitFirstOrdering<?> that = (ExplicitFirstOrdering<?>) object;
            return this.rankMap.equals(that.rankMap);
        }

        return false;
    }

    @Override
    public int hashCode() {
        return rankMap.hashCode();
    }

    @Override
    public String toString() {
        return "Ordering.explicitFirst(" + rankMap.keySet() + ")";
    }
}