74 lines
3.3 KiB
Java
74 lines
3.3 KiB
Java
/*
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* Copyright 2015 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License,
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* version 2.0 (the "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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package io.netty.util;
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/**
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* Abstraction for hash code generation and equality comparison.
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*/
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public interface HashingStrategy<T> {
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/**
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* Generate a hash code for {@code obj}.
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* <p>
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* This method must obey the same relationship that {@link java.lang.Object#hashCode()} has with
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* {@link java.lang.Object#equals(Object)}:
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* <ul>
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* <li>Calling this method multiple times with the same {@code obj} should return the same result</li>
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* <li>If {@link #equals(Object, Object)} with parameters {@code a} and {@code b} returns {@code true}
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* then the return value for this method for parameters {@code a} and {@code b} must return the same result</li>
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* <li>If {@link #equals(Object, Object)} with parameters {@code a} and {@code b} returns {@code false}
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* then the return value for this method for parameters {@code a} and {@code b} does <strong>not</strong> have to
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* return different results results. However this property is desirable.</li>
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* <li>if {@code obj} is {@code null} then this method return {@code 0}</li>
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* </ul>
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*/
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int hashCode(T obj);
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/**
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* Returns {@code true} if the arguments are equal to each other and {@code false} otherwise.
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* This method has the following restrictions:
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* <ul>
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* <li><i>reflexive</i> - {@code equals(a, a)} should return true</li>
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* <li><i>symmetric</i> - {@code equals(a, b)} returns {@code true} if {@code equals(b, a)} returns
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* {@code true}</li>
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* <li><i>transitive</i> - if {@code equals(a, b)} returns {@code true} and {@code equals(a, c)} returns
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* {@code true} then {@code equals(b, c)} should also return {@code true}</li>
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* <li><i>consistent</i> - {@code equals(a, b)} should return the same result when called multiple times
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* assuming {@code a} and {@code b} remain unchanged relative to the comparison criteria</li>
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* <li>if {@code a} and {@code b} are both {@code null} then this method returns {@code true}</li>
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* <li>if {@code a} is {@code null} and {@code b} is non-{@code null}, or {@code a} is non-{@code null} and
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* {@code b} is {@code null} then this method returns {@code false}</li>
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* </ul>
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*/
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boolean equals(T a, T b);
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/**
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* A {@link HashingStrategy} which delegates to java's {@link Object#hashCode()}
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* and {@link Object#equals(Object)}.
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*/
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@SuppressWarnings("rawtypes")
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HashingStrategy JAVA_HASHER = new HashingStrategy() {
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@Override
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public int hashCode(Object obj) {
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return obj != null ? obj.hashCode() : 0;
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}
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@Override
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public boolean equals(Object a, Object b) {
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return (a == b) || (a != null && a.equals(b));
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}
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};
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}
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