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Apache Ignite® is a Distributed Database For High-Performance Computing With In-Memory Speed.

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/*
 * 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.ignite.ml.tree.impurity;

import java.io.Serializable;

/**
 * Base interface for impurity measures that can be used in distributed decision tree algorithm.
 *
 * @param  Type of this impurity measure.
 */
public interface ImpurityMeasure> extends Comparable, Serializable {
    /**
     * Calculates impurity measure as a single double value.
     *
     * @return Impurity measure value.
     */
    public double impurity();

    /**
     * Adds the given impurity to this.
     *
     * @param measure Another impurity.
     * @return Sum of this and the given impurity.
     */
    public T add(T measure);

    /**
     * Subtracts the given impurity for this.
     *
     * @param measure Another impurity.
     * @return Difference of this and the given impurity.
     */
    public T subtract(T measure);

    /** {@inheritDoc} */
    default public int compareTo(T o) {
        return Double.compare(impurity(), o.impurity());
    }
}