io.netty.util.HashingStrategy Maven / Gradle / Ivy
/*
* 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:
*
* 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 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));
}
};
}