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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.harmony.misc;
/**
* This class is a convenience method to sequentially calculate hash code of the
* object based on the field values. The result depends on the order of elements
* appended. The exact formula is the same as for
* <code>java.util.List.hashCode</code>.
*
* If you need order independent hash code just summate, multiply or XOR all
* elements.
*
* <p>
* Suppose we have class:
*
* <pre><code>
* class Thing {
* long id;
* String name;
* float weight;
* }
* </code></pre>
*
* The hash code calculation can be expressed in 2 forms.
*
* <p>
* For maximum performance:
*
* <pre><code>
* public int hashCode() {
* int hashCode = HashCode.EMPTY_HASH_CODE;
* hashCode = HashCode.combine(hashCode, id);
* hashCode = HashCode.combine(hashCode, name);
* hashCode = HashCode.combine(hashCode, weight);
* return hashCode;
* }
* </code></pre>
*
* <p>
* For convenience: <code><pre>
* public int hashCode() {
* return new HashCode().append(id).append(name).append(weight).hashCode();
* }
* </code></pre>
*
* @see java.util.List#hashCode()
*/
public final class HashCode {
/**
* The hashCode value before any data is appended, equals to 1.
* @see java.util.List#hashCode()
*/
public static final int EMPTY_HASH_CODE = 1;
private int hashCode = EMPTY_HASH_CODE;
/**
* Returns accumulated hashCode
*/
public final int hashCode() {
return hashCode;
}
/**
* Combines hashCode of previous elements sequence and value's hashCode.
* @param hashCode previous hashCode value
* @param value new element
* @return combined hashCode
*/
public static int combine(int hashCode, boolean value) {
int v = value ? 1231 : 1237;
return combine(hashCode, v);
}
/**
* Combines hashCode of previous elements sequence and value's hashCode.
* @param hashCode previous hashCode value
* @param value new element
* @return combined hashCode
*/
public static int combine(int hashCode, long value) {
int v = (int) (value ^ (value >>> 32));
return combine(hashCode, v);
}
/**
* Combines hashCode of previous elements sequence and value's hashCode.
* @param hashCode previous hashCode value
* @param value new element
* @return combined hashCode
*/
public static int combine(int hashCode, float value) {
int v = Float.floatToIntBits(value);
return combine(hashCode, v);
}
/**
* Combines hashCode of previous elements sequence and value's hashCode.
* @param hashCode previous hashCode value
* @param value new element
* @return combined hashCode
*/
public static int combine(int hashCode, double value) {
long v = Double.doubleToLongBits(value);
return combine(hashCode, v);
}
/**
* Combines hashCode of previous elements sequence and value's hashCode.
* @param hashCode previous hashCode value
* @param value new element
* @return combined hashCode
*/
public static int combine(int hashCode, Object value) {
return combine(hashCode, value.hashCode());
}
/**
* Combines hashCode of previous elements sequence and value's hashCode.
* @param hashCode previous hashCode value
* @param value new element
* @return combined hashCode
*/
public static int combine(int hashCode, int value) {
return 31 * hashCode + value;
}
/**
* Appends value's hashCode to the current hashCode.
* @param value new element
* @return this
*/
public final HashCode append(int value) {
hashCode = combine(hashCode, value);
return this;
}
/**
* Appends value's hashCode to the current hashCode.
* @param value new element
* @return this
*/
public final HashCode append(long value) {
hashCode = combine(hashCode, value);
return this;
}
/**
* Appends value's hashCode to the current hashCode.
* @param value new element
* @return this
*/
public final HashCode append(float value) {
hashCode = combine(hashCode, value);
return this;
}
/**
* Appends value's hashCode to the current hashCode.
* @param value new element
* @return this
*/
public final HashCode append(double value) {
hashCode = combine(hashCode, value);
return this;
}
/**
* Appends value's hashCode to the current hashCode.
* @param value new element
* @return this
*/
public final HashCode append(boolean value) {
hashCode = combine(hashCode, value);
return this;
}
/**
* Appends value's hashCode to the current hashCode.
* @param value new element
* @return this
*/
public final HashCode append(Object value) {
hashCode = combine(hashCode, value);
return this;
}
}
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