juneau-core/juneau-marshall/src/main/java/org/apache/juneau/internal/HashCode.java

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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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package org.apache.juneau.internal;

/**
 * Utility class for generating integer hash codes.
 *
 * <p>
 * General usage:
 * <p class='bcode w800'>
 * 	int hashCode = new HashCode().add("foobar").add(myobject).add(123).get();
 * </p>
 */
public class HashCode {

	private int hashCode = 1;

	/**
	 * Create a new HashCode object.
	 *
	 * @return A new HashCode object.
	 */
	public static final HashCode create() {
		return new HashCode();
	}

	/**
	 * Hashes the hashcode of the specified object into this object.
	 *
	 * @param o The object whose hashcode will be hashed with this object.
	 * @return This object (for method chaining).
	 */
	public HashCode add(Object o) {
		o = unswap(o);
		add(o == null ? 1 : o.hashCode());
		return this;
	}

	/**
	 * Hashes the hashcode into this object.
	 *
	 * <p>
	 * The formula is simply <c>hashCode = 31*hashCode + i;</c>
	 *
	 * @param i The hashcode to hash into this object's hashcode.
	 * @return This object (for method chaining).
	 */
	public HashCode add(int i) {
		hashCode = 31*hashCode + i;
		return this;
	}

	/**
	 * Return the calculated hashcode value.
	 *
	 * @return The calculated hashcode.
	 */
	public int get() {
		return hashCode;
	}

	/**
	 * Converts the object to a normalized form before grabbing it's hashcode.
	 *
	 * <p>
	 * Subclasses can override this method to provide specialized handling (e.g. converting numbers to strings so that
	 * <c>123</c> and <js>"123"</js> end up creating the same hashcode.)
	 *
	 * <p>
	 * Default implementation does nothing.
	 *
	 * @param o The object to normalize before getting it's hashcode.
	 * @return The normalized object.
	 */
	protected Object unswap(Object o) {
		return o;
	}
}