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/*
 * Copyright 2015 The Netty Project
 *
 * The Netty Project 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:
 *
 *   https://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 io.netty.util;

/**
 * Abstraction for hash code generation and equality comparison.
 */
public interface HashingStrategy {
    /**
     * Generate a hash code for {@code obj}.
     * 

* This method must obey the same relationship that {@link java.lang.Object#hashCode()} has with * {@link java.lang.Object#equals(Object)}: *

    *
  • Calling this method multiple times with the same {@code obj} should return the same result
  • *
  • If {@link #equals(Object, Object)} with parameters {@code a} and {@code b} returns {@code true} * then the return value for this method for parameters {@code a} and {@code b} must return the same result
  • *
  • If {@link #equals(Object, Object)} with parameters {@code a} and {@code b} returns {@code false} * then the return value for this method for parameters {@code a} and {@code b} does not have to * return different results results. However this property is desirable.
  • *
  • if {@code obj} is {@code null} then this method return {@code 0}
  • *
*/ int hashCode(T obj); /** * Returns {@code true} if the arguments are equal to each other and {@code false} otherwise. * This method has the following restrictions: *
    *
  • reflexive - {@code equals(a, a)} should return true
  • *
  • symmetric - {@code equals(a, b)} returns {@code true} if {@code equals(b, a)} returns * {@code true}
  • *
  • transitive - if {@code equals(a, b)} returns {@code true} and {@code equals(a, c)} returns * {@code true} then {@code equals(b, c)} should also return {@code true}
  • *
  • consistent - {@code equals(a, b)} should return the same result when called multiple times * assuming {@code a} and {@code b} remain unchanged relative to the comparison criteria
  • *
  • if {@code a} and {@code b} are both {@code null} then this method returns {@code true}
  • *
  • if {@code a} is {@code null} and {@code b} is non-{@code null}, or {@code a} is non-{@code null} and * {@code b} is {@code null} then this method returns {@code false}
  • *
*/ boolean equals(T a, T b); /** * A {@link HashingStrategy} which delegates to java's {@link Object#hashCode()} * and {@link Object#equals(Object)}. */ @SuppressWarnings("rawtypes") HashingStrategy JAVA_HASHER = new HashingStrategy() { @Override public int hashCode(Object obj) { return obj != null ? obj.hashCode() : 0; } @Override public boolean equals(Object a, Object b) { return (a == b) || (a != null && a.equals(b)); } }; }




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