The Calendar class defines the constants for the MONTH field as follows.

    /**
     * Value of the {@link #MONTH} field indicating the
     * first month of the year.
     */
    public final static int JANUARY = 0;

    /**
     * Value of the {@link #MONTH} field indicating the
     * second month of the year.
     */
    public final static int FEBRUARY = 1;

etc.

However, the definitions are not applicable to other calendar systems, like Japanese imperial calendar system. For example, the Showa era started on December 26, 1926. So, December is the first (and only) month of Showa Gannen (year 1).
###@###.### 2005-2-25 07:33:32 GMT
###@###.### 2005-05-25 13:51:12 GMT