Java tutorial
/* * Copyright 2001-2010 Stephen Colebourne * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.joda.time; import org.joda.convert.FromString; import org.joda.convert.ToString; import org.joda.time.base.BaseSingleFieldPeriod; import org.joda.time.field.FieldUtils; import org.joda.time.format.ISOPeriodFormat; import org.joda.time.format.PeriodFormatter; /** * An immutable time period representing a number of months. * <p> * <code>Months</code> is an immutable period that can only store months. * It does not store years, days or hours for example. As such it is a * type-safe way of representing a number of months in an application. * <p> * The number of months is set in the constructor, and may be queried using * <code>getMonths()</code>. Basic mathematical operations are provided - * <code>plus()</code>, <code>minus()</code>, <code>multipliedBy()</code> and * <code>dividedBy()</code>. * <p> * <code>Months</code> is thread-safe and immutable. * * @author Stephen Colebourne * @since 1.4 */ public final class Months extends BaseSingleFieldPeriod { /** Constant representing zero months. */ public static final Months ZERO = new Months(0); /** Constant representing one month. */ public static final Months ONE = new Months(1); /** Constant representing two months. */ public static final Months TWO = new Months(2); /** Constant representing three months. */ public static final Months THREE = new Months(3); /** Constant representing four months. */ public static final Months FOUR = new Months(4); /** Constant representing five months. */ public static final Months FIVE = new Months(5); /** Constant representing six months. */ public static final Months SIX = new Months(6); /** Constant representing seven months. */ public static final Months SEVEN = new Months(7); /** Constant representing eight months. */ public static final Months EIGHT = new Months(8); /** Constant representing nine months. */ public static final Months NINE = new Months(9); /** Constant representing ten months. */ public static final Months TEN = new Months(10); /** Constant representing eleven months. */ public static final Months ELEVEN = new Months(11); /** Constant representing twelve months. */ public static final Months TWELVE = new Months(12); /** Constant representing the maximum number of months that can be stored in this object. */ public static final Months MAX_VALUE = new Months(Integer.MAX_VALUE); /** Constant representing the minimum number of months that can be stored in this object. */ public static final Months MIN_VALUE = new Months(Integer.MIN_VALUE); /** The parser to use for this class. */ private static final PeriodFormatter PARSER = ISOPeriodFormat.standard().withParseType(PeriodType.months()); /** Serialization version. */ private static final long serialVersionUID = 87525275727380867L; //----------------------------------------------------------------------- /** * Obtains an instance of <code>Months</code> that may be cached. * <code>Months</code> is immutable, so instances can be cached and shared. * This factory method provides access to shared instances. * * @param months the number of months to obtain an instance for * @return the instance of Months */ public static Months months(int months) { switch (months) { case 0: return ZERO; case 1: return ONE; case 2: return TWO; case 3: return THREE; case 4: return FOUR; case 5: return FIVE; case 6: return SIX; case 7: return SEVEN; case 8: return EIGHT; case 9: return NINE; case 10: return TEN; case 11: return ELEVEN; case 12: return TWELVE; case Integer.MAX_VALUE: return MAX_VALUE; case Integer.MIN_VALUE: return MIN_VALUE; default: return new Months(months); } } //----------------------------------------------------------------------- /** * Creates a <code>Months</code> representing the number of whole months * between the two specified datetimes. This method correctly handles * any daylight savings time changes that may occur during the interval. * <p> * This method calculates by adding months to the start date until the result * is past the end date. As such, a period from the end of a "long" month to * the end of a "short" month is counted as a whole month. * * @param start the start instant, must not be null * @param end the end instant, must not be null * @return the period in months * @throws IllegalArgumentException if the instants are null or invalid */ public static Months monthsBetween(ReadableInstant start, ReadableInstant end) { int amount = BaseSingleFieldPeriod.between(start, end, DurationFieldType.months()); return Months.months(amount); } /** * Creates a <code>Months</code> representing the number of whole months * between the two specified partial datetimes. * <p> * The two partials must contain the same fields, for example you can specify * two <code>LocalDate</code> objects. * <p> * This method calculates by adding months to the start date until the result * is past the end date. As such, a period from the end of a "long" month to * the end of a "short" month is counted as a whole month. * * @param start the start partial date, must not be null * @param end the end partial date, must not be null * @return the period in months * @throws IllegalArgumentException if the partials are null or invalid */ public static Months monthsBetween(ReadablePartial start, ReadablePartial end) { if (start instanceof LocalDate && end instanceof LocalDate) { Chronology chrono = DateTimeUtils.getChronology(start.getChronology()); int months = chrono.months().getDifference(((LocalDate) end).getLocalMillis(), ((LocalDate) start).getLocalMillis()); return Months.months(months); } int amount = BaseSingleFieldPeriod.between(start, end, ZERO); return Months.months(amount); } /** * Creates a <code>Months</code> representing the number of whole months * in the specified interval. This method correctly handles any daylight * savings time changes that may occur during the interval. * * @param interval the interval to extract months from, null returns zero * @return the period in months * @throws IllegalArgumentException if the partials are null or invalid */ public static Months monthsIn(ReadableInterval interval) { if (interval == null) { return Months.ZERO; } int amount = BaseSingleFieldPeriod.between(interval.getStart(), interval.getEnd(), DurationFieldType.months()); return Months.months(amount); } /** * Creates a new <code>Months</code> by parsing a string in the ISO8601 format 'PnM'. * <p> * The parse will accept the full ISO syntax of PnYnMnWnDTnHnMnS however only the * months component may be non-zero. If any other component is non-zero, an exception * will be thrown. * * @param periodStr the period string, null returns zero * @return the period in months * @throws IllegalArgumentException if the string format is invalid */ @FromString public static Months parseMonths(String periodStr) { if (periodStr == null) { return Months.ZERO; } Period p = PARSER.parsePeriod(periodStr); return Months.months(p.getMonths()); } //----------------------------------------------------------------------- /** * Creates a new instance representing a number of months. * You should consider using the factory method {@link #months(int)} * instead of the constructor. * * @param months the number of months to represent */ private Months(int months) { super(months); } /** * Resolves singletons. * * @return the singleton instance */ private Object readResolve() { return Months.months(getValue()); } //----------------------------------------------------------------------- /** * Gets the duration field type, which is <code>months</code>. * * @return the period type */ public DurationFieldType getFieldType() { return DurationFieldType.months(); } /** * Gets the period type, which is <code>months</code>. * * @return the period type */ public PeriodType getPeriodType() { return PeriodType.months(); } //----------------------------------------------------------------------- /** * Gets the number of months that this period represents. * * @return the number of months in the period */ public int getMonths() { return getValue(); } //----------------------------------------------------------------------- /** * Returns a new instance with the specified number of months added. * <p> * This instance is immutable and unaffected by this method call. * * @param months the amount of months to add, may be negative * @return the new period plus the specified number of months * @throws ArithmeticException if the result overflows an int */ public Months plus(int months) { if (months == 0) { return this; } return Months.months(FieldUtils.safeAdd(getValue(), months)); } /** * Returns a new instance with the specified number of months added. * <p> * This instance is immutable and unaffected by this method call. * * @param months the amount of months to add, may be negative, null means zero * @return the new period plus the specified number of months * @throws ArithmeticException if the result overflows an int */ public Months plus(Months months) { if (months == null) { return this; } return plus(months.getValue()); } //----------------------------------------------------------------------- /** * Returns a new instance with the specified number of months taken away. * <p> * This instance is immutable and unaffected by this method call. * * @param months the amount of months to take away, may be negative * @return the new period minus the specified number of months * @throws ArithmeticException if the result overflows an int */ public Months minus(int months) { return plus(FieldUtils.safeNegate(months)); } /** * Returns a new instance with the specified number of months taken away. * <p> * This instance is immutable and unaffected by this method call. * * @param months the amount of months to take away, may be negative, null means zero * @return the new period minus the specified number of months * @throws ArithmeticException if the result overflows an int */ public Months minus(Months months) { if (months == null) { return this; } return minus(months.getValue()); } //----------------------------------------------------------------------- /** * Returns a new instance with the months multiplied by the specified scalar. * <p> * This instance is immutable and unaffected by this method call. * * @param scalar the amount to multiply by, may be negative * @return the new period multiplied by the specified scalar * @throws ArithmeticException if the result overflows an int */ public Months multipliedBy(int scalar) { return Months.months(FieldUtils.safeMultiply(getValue(), scalar)); } /** * Returns a new instance with the months divided by the specified divisor. * The calculation uses integer division, thus 3 divided by 2 is 1. * <p> * This instance is immutable and unaffected by this method call. * * @param divisor the amount to divide by, may be negative * @return the new period divided by the specified divisor * @throws ArithmeticException if the divisor is zero */ public Months dividedBy(int divisor) { if (divisor == 1) { return this; } return Months.months(getValue() / divisor); } //----------------------------------------------------------------------- /** * Returns a new instance with the months value negated. * * @return the new period with a negated value * @throws ArithmeticException if the result overflows an int */ public Months negated() { return Months.months(FieldUtils.safeNegate(getValue())); } //----------------------------------------------------------------------- /** * Is this months instance greater than the specified number of months. * * @param other the other period, null means zero * @return true if this months instance is greater than the specified one */ public boolean isGreaterThan(Months other) { if (other == null) { return getValue() > 0; } return getValue() > other.getValue(); } /** * Is this months instance less than the specified number of months. * * @param other the other period, null means zero * @return true if this months instance is less than the specified one */ public boolean isLessThan(Months other) { if (other == null) { return getValue() < 0; } return getValue() < other.getValue(); } //----------------------------------------------------------------------- /** * Gets this instance as a String in the ISO8601 duration format. * <p> * For example, "P4M" represents 4 months. * * @return the value as an ISO8601 string */ @ToString public String toString() { return "P" + String.valueOf(getValue()) + "M"; } }