Какдокументация в состояниях Object.hashCode (),

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)

Таким образом, язык Java не требует, чтобы хеш-код класса Object возвращал адрес памяти объекта, и поэтому вам не следует полагаться на это.

Вы всегда можете проверить, посмотрев на источник, который поставляется с вашим JDK.

мойjava.lang.Object шоуhashCode как родной метод. Вот явадаки.

/**
 * Returns a hash code value for the object. This method is 
 * supported for the benefit of hashtables such as those provided by 
 * <code>java.util.Hashtable</code>. 
 * <p>
 * The general contract of <code>hashCode</code> is: 
 * <ul>
 * <li>Whenever it is invoked on the same object more than once during 
 *     an execution of a Java application, the <tt>hashCode</tt> method 
 *     must consistently return the same integer, provided no information 
 *     used in <tt>equals</tt> comparisons on the object is modified.
 *     This integer need not remain consistent from one execution of an
 *     application to another execution of the same application. 
 * <li>If two objects are equal according to the <tt>equals(Object)</tt>
 *     method, then calling the <code>hashCode</code> method on each of 
 *     the two objects must produce the same integer result. 
 * <li>It is <em>not</em> required that if two objects are unequal 
 *     according to the {@link java.lang.Object#equals(java.lang.Object)} 
 *     method, then calling the <tt>hashCode</tt> method on each of the 
 *     two objects must produce distinct integer results.  However, the 
 *     programmer should be aware that producing distinct integer results 
 *     for unequal objects may improve the performance of hashtables.
 * </ul>
 * <p>
 * As much as is reasonably practical, the hashCode method defined by 
 * class <tt>Object</tt> does return distinct integers for distinct 
 * objects. (This is typically implemented by converting the internal 
 * address of the object into an integer, but this implementation 
 * technique is not required by the 
 * Java<font size="-2"><sup>TM</sup></font> programming language.)
 *
 * @return  a hash code value for this object.
 * @see     java.lang.Object#equals(java.lang.Object)
 * @see     java.util.Hashtable
 */
public native int hashCode();

Нет, функция HashCode () возвращает целое число. Если вы не определили функцию HashCode () для своего объекта, Java МОЖЕТ преобразовать адрес памяти объекта в целое число и вернуть его.