java.util.Comparator Maven / Gradle / Ivy
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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 java.util;
/**
* A {@code Comparator} is used to compare two objects to determine their ordering with
* respect to each other. On a given {@code Collection}, a {@code Comparator} can be used to
* obtain a sorted {@code Collection} which is totally ordered. For a {@code Comparator}
* to be consistent with equals, its {code #compare(Object, Object)}
* method has to return zero for each pair of elements (a,b) where a.equals(b)
* holds true. It is recommended that a {@code Comparator} implements
* {@link java.io.Serializable}.
*
* @since 1.2
*/
public interface Comparator {
/**
* Compares the two specified objects to determine their relative ordering. The ordering
* implied by the return value of this method for all possible pairs of
* {@code (object1, object2)} should form an equivalence relation.
* This means that
*
* - {@code compare(a,a)} returns zero for all {@code a}
* - the sign of {@code compare(a,b)} must be the opposite of the sign of {@code
* compare(b,a)} for all pairs of (a,b)
* - From {@code compare(a,b) > 0} and {@code compare(b,c) > 0} it must
* follow {@code compare(a,c) > 0} for all possible combinations of {@code
* (a,b,c)}
*
*
* @param object1
* an {@code Object}.
* @param object2
* a second {@code Object} to compare with {@code object1}.
* @return an integer < 0 if {@code object1} is less than {@code object2}, 0 if they are
* equal, and > 0 if {@code object1} is greater than {@code object2}.
* @throws ClassCastException
* if objects are not of the correct type.
*/
public int compare(T object1, T object2);
/**
* Compares this {@code Comparator} with the specified {@code Object} and indicates whether they
* are equal. In order to be equal, {@code object} must represent the same object
* as this instance using a class-specific comparison.
*
* A {@code Comparator} never needs to override this method, but may choose so for
* performance reasons.
*
* @param object
* the {@code Object} to compare with this comparator.
* @return boolean {@code true} if specified {@code Object} is the same as this
* {@code Object}, and {@code false} otherwise.
* @see Object#hashCode
* @see Object#equals
*/
public boolean equals(Object object);
}