org.apache.harmony.misc.HashCode Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of afirma-lib-itext-android Show documentation
Version modificada de iText 2.1.7 con el paquete cambiado, adaptaciones menores para firma y dependencias actualizadas.
There is a newer version: 1.5
Show newest version
/*
 *  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
 * 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 this.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) {
		final 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) {
		final 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) {
		final 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) {
		final 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) {
		this.hashCode = combine(this.hashCode, value);
		return this;
	}

	/**
	 * Appends value's hashCode to the current hashCode.
	 *
	 * @param value
	 *            new element
	 * @return this
	 */
	public final HashCode append(long value) {
		this.hashCode = combine(this.hashCode, value);
		return this;
	}

	/**
	 * Appends value's hashCode to the current hashCode.
	 *
	 * @param value
	 *            new element
	 * @return this
	 */
	public final HashCode append(float value) {
		this.hashCode = combine(this.hashCode, value);
		return this;
	}

	/**
	 * Appends value's hashCode to the current hashCode.
	 *
	 * @param value
	 *            new element
	 * @return this
	 */
	public final HashCode append(double value) {
		this.hashCode = combine(this.hashCode, value);
		return this;
	}

	/**
	 * Appends value's hashCode to the current hashCode.
	 *
	 * @param value
	 *            new element
	 * @return this
	 */
	public final HashCode append(boolean value) {
		this.hashCode = combine(this.hashCode, value);
		return this;
	}

	/**
	 * Appends value's hashCode to the current hashCode.
	 *
	 * @param value
	 *            new element
	 * @return this
	 */
	public final HashCode append(Object value) {
		this.hashCode = combine(this.hashCode, value);
		return this;
	}
}