ChronoPeriod.java

/*
 * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * Copyright (c) 2013, Stephen Colebourne & Michael Nascimento Santos
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  * Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 *  * Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 *  * Neither the name of JSR-310 nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package java.time.chrono;

import java.time.DateTimeException;
import java.time.temporal.ChronoUnit;
import java.time.temporal.Temporal;
import java.time.temporal.TemporalAmount;
import java.time.temporal.TemporalUnit;
import java.time.temporal.UnsupportedTemporalTypeException;
import java.util.List;
import java.util.Objects;

/**
 * A date-based amount of time, such as '3 years, 4 months and 5 days' in an
 * arbitrary chronology, intended for advanced globalization use cases.
 * <p>
 * This interface models a date-based amount of time in a calendar system.
 * While most calendar systems use years, months and days, some do not.
 * Therefore, this interface operates solely in terms of a set of supported
 * units that are defined by the {@code Chronology}.
 * The set of supported units is fixed for a given chronology.
 * The amount of a supported unit may be set to zero.
 * <p>
 * The period is modeled as a directed amount of time, meaning that individual
 * parts of the period may be negative.
 *
 * @implSpec This interface must be implemented with care to ensure other classes operate correctly.
 * All implementations that can be instantiated must be final, immutable and thread-safe.
 * Subclasses should be Serializable wherever possible.
 * @since 1.8
 */
// 时间段，包含年/月/日部件，精确到天；允许在子类中将"日期"部件绑定到某种历法系统
public interface ChronoPeriod extends TemporalAmount {
    
    /*▼ 部件 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Checks if all the supported units of this period are zero.
     *
     * @return true if this period is zero-length
     */
    // 判断当前"时间段"的值是否为0，即该"时间段"内所有计时部件的值为0
    default boolean isZero() {
        for(TemporalUnit unit : getUnits()) {
            if(get(unit) != 0) {
                return false;
            }
        }
        
        return true;
    }
    
    /**
     * Gets the chronology that defines the meaning of the supported units.
     * <p>
     * The period is defined by the chronology.
     * It controls the supported units and restricts addition/subtraction
     * to {@code ChronoLocalDate} instances of the same chronology.
     *
     * @return the chronology defining the period, not null
     */
    // 返回当前"时间段"采用的历法系统
    Chronology getChronology();
    
    /*▲ 部件 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 基本运算 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Returns a copy of this period with the specified period added.
     * <p>
     * If the specified amount is a {@code ChronoPeriod} then it must have
     * the same chronology as this period. Implementations may choose to
     * accept or reject other {@code TemporalAmount} implementations.
     * <p>
     * This instance is immutable and unaffected by this method call.
     *
     * @param amountToAdd the period to add, not null
     *
     * @return a {@code ChronoPeriod} based on this period with the requested period added, not null
     *
     * @throws ArithmeticException if numeric overflow occurs
     */
    /*
     * 对当前"时间段"的值与参数中的"时间段"求和
     *
     * 如果求和后的值与当前"时间段"的值相等，则直接返回当前"时间段"对象。
     * 否则，需要构造"求和"后的新对象再返回。
     */
    ChronoPeriod plus(TemporalAmount amountToAdd);
    
    /**
     * Returns a copy of this period with the specified period subtracted.
     * <p>
     * If the specified amount is a {@code ChronoPeriod} then it must have
     * the same chronology as this period. Implementations may choose to
     * accept or reject other {@code TemporalAmount} implementations.
     * <p>
     * This instance is immutable and unaffected by this method call.
     *
     * @param amountToSubtract the period to subtract, not null
     *
     * @return a {@code ChronoPeriod} based on this period with the requested period subtracted, not null
     *
     * @throws ArithmeticException if numeric overflow occurs
     */
    /*
     * 对当前"时间段"的值与参数中的"时间段"求差
     *
     * 如果求差后的值与当前"时间段"的值相等，则直接返回当前"时间段"对象。
     * 否则，需要构造"求差"后的新对象再返回。
     */
    ChronoPeriod minus(TemporalAmount amountToSubtract);
    
    /**
     * Returns a new instance with each amount in this period in this period
     * multiplied by the specified scalar.
     * <p>
     * This returns a period with each supported unit individually multiplied.
     * For example, a period of "2 years, -3 months and 4 days" multiplied by
     * 3 will return "6 years, -9 months and 12 days".
     * No normalization is performed.
     *
     * @param scalar the scalar to multiply by, not null
     *
     * @return a {@code ChronoPeriod} based on this period with the amounts multiplied
     * by the scalar, not null
     *
     * @throws ArithmeticException if numeric overflow occurs
     */
    /*
     * 在当前"时间段"的值上乘以scalar(即放大scalar倍)
     *
     * 如果乘以后的值与当前"时间段"的值相等，则直接返回当前"时间段"对象。
     * 否则，需要构造"乘以"操作后的新对象再返回。
     */
    ChronoPeriod multipliedBy(int scalar);
    
    /**
     * Returns a new instance with each amount in this period negated.
     * <p>
     * This returns a period with each supported unit individually negated.
     * For example, a period of "2 years, -3 months and 4 days" will be
     * negated to "-2 years, 3 months and -4 days".
     * No normalization is performed.
     *
     * @return a {@code ChronoPeriod} based on this period with the amounts negated, not null
     *
     * @throws ArithmeticException if numeric overflow occurs, which only happens if
     *                             one of the units has the value {@code Long.MIN_VALUE}
     */
    // 取相反数
    default ChronoPeriod negated() {
        return multipliedBy(-1);
    }
    
    /**
     * Checks if any of the supported units of this period are negative.
     *
     * @return true if any unit of this period is negative
     */
    // 判断当前"时间段"是否为负
    default boolean isNegative() {
        for(TemporalUnit unit : getUnits()) {
            if(get(unit)<0) {
                return true;
            }
        }
        return false;
    }
    
    /*▲ 基本运算 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 增加/减少 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Adds this period to the specified temporal object.
     * <p>
     * This returns a temporal object of the same observable type as the input
     * with this period added.
     * <p>
     * In most cases, it is clearer to reverse the calling pattern by using
     * {@link Temporal#plus(TemporalAmount)}.
     * <pre>
     *   // these two lines are equivalent, but the second approach is recommended
     *   dateTime = thisPeriod.addTo(dateTime);
     *   dateTime = dateTime.plus(thisPeriod);
     * </pre>
     * <p>
     * The specified temporal must have the same chronology as this period.
     * This returns a temporal with the non-zero supported units added.
     * <p>
     * This instance is immutable and unaffected by this method call.
     *
     * @param temporal the temporal object to adjust, not null
     *
     * @return an object of the same type with the adjustment made, not null
     *
     * @throws DateTimeException   if unable to add
     * @throws ArithmeticException if numeric overflow occurs
     */
    /*
     * 增加目标时间量temporal
     *
     * 尝试将当前"时间段"累加到指定的时间量temporal上，
     * 如果累加后的值与原值相同，则返回temporal自身；否则，会构造一个新对象再返回。
     */
    @Override
    Temporal addTo(Temporal temporal);
    
    /**
     * Subtracts this period from the specified temporal object.
     * <p>
     * This returns a temporal object of the same observable type as the input
     * with this period subtracted.
     * <p>
     * In most cases, it is clearer to reverse the calling pattern by using
     * {@link Temporal#minus(TemporalAmount)}.
     * <pre>
     *   // these two lines are equivalent, but the second approach is recommended
     *   dateTime = thisPeriod.subtractFrom(dateTime);
     *   dateTime = dateTime.minus(thisPeriod);
     * </pre>
     * <p>
     * The specified temporal must have the same chronology as this period.
     * This returns a temporal with the non-zero supported units subtracted.
     * <p>
     * This instance is immutable and unaffected by this method call.
     *
     * @param temporal the temporal object to adjust, not null
     *
     * @return an object of the same type with the adjustment made, not null
     *
     * @throws DateTimeException   if unable to subtract
     * @throws ArithmeticException if numeric overflow occurs
     */
    /*
     * 减少目标时间量temporal
     *
     * 尝试从指定的时间量temporal上减去当前"时间段"，
     * 如果减少后的值与原值相同，则返回temporal自身；否则，会构造一个新对象再返回。
     */
    @Override
    Temporal subtractFrom(Temporal temporal);
    
    /*▲ 增加/减少 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 时间量单位 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Gets the set of units supported by this period.
     * <p>
     * The supported units are chronology specific.
     * They will typically be {@link ChronoUnit#YEARS YEARS},
     * {@link ChronoUnit#MONTHS MONTHS} and {@link ChronoUnit#DAYS DAYS}.
     * They are returned in order from largest to smallest.
     * <p>
     * This set can be used in conjunction with {@link #get(TemporalUnit)}
     * to access the entire state of the period.
     *
     * @return a list containing the supported units, not null
     */
    // 返回当前"时间段"上可用的时间量单位，这其实是该"时间段"的组成部件
    @Override
    List<TemporalUnit> getUnits();
    
    /**
     * Gets the value of the requested unit.
     * <p>
     * The supported units are chronology specific.
     * They will typically be {@link ChronoUnit#YEARS YEARS},
     * {@link ChronoUnit#MONTHS MONTHS} and {@link ChronoUnit#DAYS DAYS}.
     * Requesting an unsupported unit will throw an exception.
     *
     * @param unit the {@code TemporalUnit} for which to return the value
     *
     * @return the long value of the unit
     *
     * @throws DateTimeException                if the unit is not supported
     * @throws UnsupportedTemporalTypeException if the unit is not supported
     */
    // 返回当前"时间段"中指定的时间量单位unit对应的时间量数值
    @Override
    long get(TemporalUnit unit);
    
    /*▲ 时间量单位 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 杂项 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Obtains a {@code ChronoPeriod} consisting of amount of time between two dates.
     * <p>
     * The start date is included, but the end date is not.
     * The period is calculated using {@link ChronoLocalDate#until(ChronoLocalDate)}.
     * As such, the calculation is chronology specific.
     * <p>
     * The chronology of the first date is used.
     * The chronology of the second date is ignored, with the date being converted
     * to the target chronology system before the calculation starts.
     * <p>
     * The result of this method can be a negative period if the end is before the start.
     * In most cases, the positive/negative sign will be the same in each of the supported fields.
     *
     * @param startDateInclusive the start date, inclusive, specifying the chronology of the calculation, not null
     * @param endDateExclusive   the end date, exclusive, in any chronology, not null
     *
     * @return the period between this date and the end date, not null
     *
     * @see ChronoLocalDate#until(ChronoLocalDate)
     */
    // 计算两个时间量之间相差多少个"时间段"
    static ChronoPeriod between(ChronoLocalDate startDateInclusive, ChronoLocalDate endDateExclusive) {
        Objects.requireNonNull(startDateInclusive, "startDateInclusive");
        Objects.requireNonNull(endDateExclusive, "endDateExclusive");
        
        return startDateInclusive.until(endDateExclusive);
    }
    
    /**
     * Returns a copy of this period with the amounts of each unit normalized.
     * <p>
     * The process of normalization is specific to each calendar system.
     * For example, in the ISO calendar system, the years and months are
     * normalized but the days are not, such that "15 months" would be
     * normalized to "1 year and 3 months".
     * <p>
     * This instance is immutable and unaffected by this method call.
     *
     * @return a {@code ChronoPeriod} based on this period with the amounts of each
     * unit normalized, not null
     *
     * @throws ArithmeticException if numeric overflow occurs
     */
    // 返回当前"时间段"的一个规范表示：即先从比较大的单位开始填充数据
    ChronoPeriod normalized();
    
    /*▲ 杂项 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    /**
     * Outputs this period as a {@code String}.
     * <p>
     * The output will include the period amounts and chronology.
     *
     * @return a string representation of this period, not null
     */
    @Override
    String toString();
    
    /**
     * Checks if this period is equal to another period, including the chronology.
     * <p>
     * Compares this period with another ensuring that the type, each amount and
     * the chronology are the same.
     * Note that this means that a period of "15 Months" is not equal to a period
     * of "1 Year and 3 Months".
     *
     * @param obj the object to check, null returns false
     *
     * @return true if this is equal to the other period
     */
    @Override
    boolean equals(Object obj);
    
    /**
     * A hash code for this period.
     *
     * @return a suitable hash code
     */
    @Override
    int hashCode();
    
}