com.itextpdf.io.util.HashCode Maven / Gradle / Ivy
/*
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Copyright (c) 1998-2022 iText Group NV
Authors: Bruno Lowagie, Paulo Soares, et al.
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it under the terms of the GNU Affero General Public License version 3
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or FITNESS FOR A PARTICULAR PURPOSE.
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*/
package com.itextpdf.io.util;
/**
* 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
* {@link java.util.List#hashCode}.
*
* If you need order independent hash code just summate, multiply or XOR all
* elements.
*
*
* Suppose we have class:
*
*
* class Thing {
* long id;
* String name;
* float weight;
* }
*
*
* The hash code calculation can be expressed in 2 forms.
*
*
* For maximum performance:
*
*
* 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;
* }
*
*
*
* For convenience:
*
* public int hashCode() {
* return new HashCode().append(id).append(name).append(weight).hashCode();
* }
*
*
* @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
*/
@Override
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;
}
}