equals比较得是两个对象，或者是两个对象的内容，假如两个对象相等那它们两个的hashcode也必须一样，因为hashcode是用对象的内部地址转换成一个整数的。
假如你改写了equals方法而没重写hashcode方法，那就乱套了！

这是sun说的，看看Object#equals()和Object#hashCode()的文档

     * Note that it is generally necessary to override the <tt>hashCode</tt>
     * method whenever this method is overridden, so as to maintain the
     * general contract for the <tt>hashCode</tt> method, which states
     * that equal objects must have equal hash codes.

     * 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>.

equals比较得是两个对象，或者是两个对象的内容，假如两个对象相等那它们两个的hashcode也必须一样，因为hashcode是用对象的内部地址转换成一个整数的。
假如你改写了equals方法而没重写hashcode方法，那就乱套了！

这是sun说的，看看Object#equals()和Object#hashCode()的文档

     * Note that it is generally necessary to override the <tt>hashCode</tt>
     * method whenever this method is overridden, so as to maintain the
     * general contract for the <tt>hashCode</tt> method, which states
     * that equal objects must have equal hash codes.

     * 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>.