001/*
002 *  Copyright 2001-2010 Stephen Colebourne
003 *
004 *  Licensed under the Apache License, Version 2.0 (the "License");
005 *  you may not use this file except in compliance with the License.
006 *  You may obtain a copy of the License at
007 *
008 *      http://www.apache.org/licenses/LICENSE-2.0
009 *
010 *  Unless required by applicable law or agreed to in writing, software
011 *  distributed under the License is distributed on an "AS IS" BASIS,
012 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 *  See the License for the specific language governing permissions and
014 *  limitations under the License.
015 */
016package org.joda.time;
017
018import org.joda.convert.FromString;
019import org.joda.convert.ToString;
020import org.joda.time.base.BaseSingleFieldPeriod;
021import org.joda.time.field.FieldUtils;
022import org.joda.time.format.ISOPeriodFormat;
023import org.joda.time.format.PeriodFormatter;
024
025/**
026 * An immutable time period representing a number of months.
027 * <p>
028 * <code>Months</code> is an immutable period that can only store months.
029 * It does not store years, days or hours for example. As such it is a
030 * type-safe way of representing a number of months in an application.
031 * <p>
032 * The number of months is set in the constructor, and may be queried using
033 * <code>getMonths()</code>. Basic mathematical operations are provided -
034 * <code>plus()</code>, <code>minus()</code>, <code>multipliedBy()</code> and
035 * <code>dividedBy()</code>.
036 * <p>
037 * <code>Months</code> is thread-safe and immutable.
038 *
039 * @author Stephen Colebourne
040 * @since 1.4
041 */
042public final class Months extends BaseSingleFieldPeriod {
043
044    /** Constant representing zero months. */
045    public static final Months ZERO = new Months(0);
046    /** Constant representing one month. */
047    public static final Months ONE = new Months(1);
048    /** Constant representing two months. */
049    public static final Months TWO = new Months(2);
050    /** Constant representing three months. */
051    public static final Months THREE = new Months(3);
052    /** Constant representing four months. */
053    public static final Months FOUR = new Months(4);
054    /** Constant representing five months. */
055    public static final Months FIVE = new Months(5);
056    /** Constant representing six months. */
057    public static final Months SIX = new Months(6);
058    /** Constant representing seven months. */
059    public static final Months SEVEN = new Months(7);
060    /** Constant representing eight months. */
061    public static final Months EIGHT = new Months(8);
062    /** Constant representing nine months. */
063    public static final Months NINE = new Months(9);
064    /** Constant representing ten months. */
065    public static final Months TEN = new Months(10);
066    /** Constant representing eleven months. */
067    public static final Months ELEVEN = new Months(11);
068    /** Constant representing twelve months. */
069    public static final Months TWELVE = new Months(12);
070    /** Constant representing the maximum number of months that can be stored in this object. */
071    public static final Months MAX_VALUE = new Months(Integer.MAX_VALUE);
072    /** Constant representing the minimum number of months that can be stored in this object. */
073    public static final Months MIN_VALUE = new Months(Integer.MIN_VALUE);
074
075    /** The parser to use for this class. */
076    private static final PeriodFormatter PARSER = ISOPeriodFormat.standard().withParseType(PeriodType.months());
077    /** Serialization version. */
078    private static final long serialVersionUID = 87525275727380867L;
079
080    //-----------------------------------------------------------------------
081    /**
082     * Obtains an instance of <code>Months</code> that may be cached.
083     * <code>Months</code> is immutable, so instances can be cached and shared.
084     * This factory method provides access to shared instances.
085     *
086     * @param months  the number of months to obtain an instance for
087     * @return the instance of Months
088     */
089    public static Months months(int months) {
090        switch (months) {
091            case 0:
092                return ZERO;
093            case 1:
094                return ONE;
095            case 2:
096                return TWO;
097            case 3:
098                return THREE;
099            case 4:
100                return FOUR;
101            case 5:
102                return FIVE;
103            case 6:
104                return SIX;
105            case 7:
106                return SEVEN;
107            case 8:
108                return EIGHT;
109            case 9:
110                return NINE;
111            case 10:
112                return TEN;
113            case 11:
114                return ELEVEN;
115            case 12:
116                return TWELVE;
117            case Integer.MAX_VALUE:
118                return MAX_VALUE;
119            case Integer.MIN_VALUE:
120                return MIN_VALUE;
121            default:
122                return new Months(months);
123        }
124    }
125
126    //-----------------------------------------------------------------------
127    /**
128     * Creates a <code>Months</code> representing the number of whole months
129     * between the two specified datetimes. This method corectly handles
130     * any daylight savings time changes that may occur during the interval.
131     *
132     * @param start  the start instant, must not be null
133     * @param end  the end instant, must not be null
134     * @return the period in months
135     * @throws IllegalArgumentException if the instants are null or invalid
136     */
137    public static Months monthsBetween(ReadableInstant start, ReadableInstant end) {
138        int amount = BaseSingleFieldPeriod.between(start, end, DurationFieldType.months());
139        return Months.months(amount);
140    }
141
142    /**
143     * Creates a <code>Months</code> representing the number of whole months
144     * between the two specified partial datetimes.
145     * <p>
146     * The two partials must contain the same fields, for example you can specify
147     * two <code>LocalDate</code> objects.
148     *
149     * @param start  the start partial date, must not be null
150     * @param end  the end partial date, must not be null
151     * @return the period in months
152     * @throws IllegalArgumentException if the partials are null or invalid
153     */
154    public static Months monthsBetween(ReadablePartial start, ReadablePartial end) {
155        if (start instanceof LocalDate && end instanceof LocalDate)   {
156            Chronology chrono = DateTimeUtils.getChronology(start.getChronology());
157            int months = chrono.months().getDifference(
158                    ((LocalDate) end).getLocalMillis(), ((LocalDate) start).getLocalMillis());
159            return Months.months(months);
160        }
161        int amount = BaseSingleFieldPeriod.between(start, end, ZERO);
162        return Months.months(amount);
163    }
164
165    /**
166     * Creates a <code>Months</code> representing the number of whole months
167     * in the specified interval. This method corectly handles any daylight
168     * savings time changes that may occur during the interval.
169     *
170     * @param interval  the interval to extract months from, null returns zero
171     * @return the period in months
172     * @throws IllegalArgumentException if the partials are null or invalid
173     */
174    public static Months monthsIn(ReadableInterval interval) {
175        if (interval == null)   {
176            return Months.ZERO;
177        }
178        int amount = BaseSingleFieldPeriod.between(interval.getStart(), interval.getEnd(), DurationFieldType.months());
179        return Months.months(amount);
180    }
181
182    /**
183     * Creates a new <code>Months</code> by parsing a string in the ISO8601 format 'PnM'.
184     * <p>
185     * The parse will accept the full ISO syntax of PnYnMnWnDTnHnMnS however only the
186     * months component may be non-zero. If any other component is non-zero, an exception
187     * will be thrown.
188     *
189     * @param periodStr  the period string, null returns zero
190     * @return the period in months
191     * @throws IllegalArgumentException if the string format is invalid
192     */
193    @FromString
194    public static Months parseMonths(String periodStr) {
195        if (periodStr == null) {
196            return Months.ZERO;
197        }
198        Period p = PARSER.parsePeriod(periodStr);
199        return Months.months(p.getMonths());
200    }
201
202    //-----------------------------------------------------------------------
203    /**
204     * Creates a new instance representing a number of months.
205     * You should consider using the factory method {@link #months(int)}
206     * instead of the constructor.
207     *
208     * @param months  the number of months to represent
209     */
210    private Months(int months) {
211        super(months);
212    }
213
214    /**
215     * Resolves singletons.
216     * 
217     * @return the singleton instance
218     */
219    private Object readResolve() {
220        return Months.months(getValue());
221    }
222
223    //-----------------------------------------------------------------------
224    /**
225     * Gets the duration field type, which is <code>months</code>.
226     *
227     * @return the period type
228     */
229    public DurationFieldType getFieldType() {
230        return DurationFieldType.months();
231    }
232
233    /**
234     * Gets the period type, which is <code>months</code>.
235     *
236     * @return the period type
237     */
238    public PeriodType getPeriodType() {
239        return PeriodType.months();
240    }
241
242    //-----------------------------------------------------------------------
243    /**
244     * Gets the number of months that this period represents.
245     *
246     * @return the number of months in the period
247     */
248    public int getMonths() {
249        return getValue();
250    }
251
252    //-----------------------------------------------------------------------
253    /**
254     * Returns a new instance with the specified number of months added.
255     * <p>
256     * This instance is immutable and unaffected by this method call.
257     *
258     * @param months  the amount of months to add, may be negative
259     * @return the new period plus the specified number of months
260     * @throws ArithmeticException if the result overflows an int
261     */
262    public Months plus(int months) {
263        if (months == 0) {
264            return this;
265        }
266        return Months.months(FieldUtils.safeAdd(getValue(), months));
267    }
268
269    /**
270     * Returns a new instance with the specified number of months added.
271     * <p>
272     * This instance is immutable and unaffected by this method call.
273     *
274     * @param months  the amount of months to add, may be negative, null means zero
275     * @return the new period plus the specified number of months
276     * @throws ArithmeticException if the result overflows an int
277     */
278    public Months plus(Months months) {
279        if (months == null) {
280            return this;
281        }
282        return plus(months.getValue());
283    }
284
285    //-----------------------------------------------------------------------
286    /**
287     * Returns a new instance with the specified number of months taken away.
288     * <p>
289     * This instance is immutable and unaffected by this method call.
290     *
291     * @param months  the amount of months to take away, may be negative
292     * @return the new period minus the specified number of months
293     * @throws ArithmeticException if the result overflows an int
294     */
295    public Months minus(int months) {
296        return plus(FieldUtils.safeNegate(months));
297    }
298
299    /**
300     * Returns a new instance with the specified number of months taken away.
301     * <p>
302     * This instance is immutable and unaffected by this method call.
303     *
304     * @param months  the amount of months to take away, may be negative, null means zero
305     * @return the new period minus the specified number of months
306     * @throws ArithmeticException if the result overflows an int
307     */
308    public Months minus(Months months) {
309        if (months == null) {
310            return this;
311        }
312        return minus(months.getValue());
313    }
314
315    //-----------------------------------------------------------------------
316    /**
317     * Returns a new instance with the months multiplied by the specified scalar.
318     * <p>
319     * This instance is immutable and unaffected by this method call.
320     *
321     * @param scalar  the amount to multiply by, may be negative
322     * @return the new period multiplied by the specified scalar
323     * @throws ArithmeticException if the result overflows an int
324     */
325    public Months multipliedBy(int scalar) {
326        return Months.months(FieldUtils.safeMultiply(getValue(), scalar));
327    }
328
329    /**
330     * Returns a new instance with the months divided by the specified divisor.
331     * The calculation uses integer division, thus 3 divided by 2 is 1.
332     * <p>
333     * This instance is immutable and unaffected by this method call.
334     *
335     * @param divisor  the amount to divide by, may be negative
336     * @return the new period divided by the specified divisor
337     * @throws ArithmeticException if the divisor is zero
338     */
339    public Months dividedBy(int divisor) {
340        if (divisor == 1) {
341            return this;
342        }
343        return Months.months(getValue() / divisor);
344    }
345
346    //-----------------------------------------------------------------------
347    /**
348     * Returns a new instance with the months value negated.
349     *
350     * @return the new period with a negated value
351     * @throws ArithmeticException if the result overflows an int
352     */
353    public Months negated() {
354        return Months.months(FieldUtils.safeNegate(getValue()));
355    }
356
357    //-----------------------------------------------------------------------
358    /**
359     * Is this months instance greater than the specified number of months.
360     *
361     * @param other  the other period, null means zero
362     * @return true if this months instance is greater than the specified one
363     */
364    public boolean isGreaterThan(Months other) {
365        if (other == null) {
366            return getValue() > 0;
367        }
368        return getValue() > other.getValue();
369    }
370
371    /**
372     * Is this months instance less than the specified number of months.
373     *
374     * @param other  the other period, null means zero
375     * @return true if this months instance is less than the specified one
376     */
377    public boolean isLessThan(Months other) {
378        if (other == null) {
379            return getValue() < 0;
380        }
381        return getValue() < other.getValue();
382    }
383
384    //-----------------------------------------------------------------------
385    /**
386     * Gets this instance as a String in the ISO8601 duration format.
387     * <p>
388     * For example, "P4M" represents 4 months.
389     *
390     * @return the value as an ISO8601 string
391     */
392    @ToString
393    public String toString() {
394        return "P" + String.valueOf(getValue()) + "M";
395    }
396
397}