ChronoPeriodImpl.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
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/*
 * 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
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package java.time.chrono;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectStreamException;
import java.io.Serializable;
import java.time.DateTimeException;
import java.time.temporal.ChronoUnit;
import java.time.temporal.Temporal;
import java.time.temporal.TemporalAccessor;
import java.time.temporal.TemporalAmount;
import java.time.temporal.TemporalQueries;
import java.time.temporal.TemporalUnit;
import java.time.temporal.UnsupportedTemporalTypeException;
import java.time.temporal.ValueRange;
import java.util.List;
import java.util.Objects;

import static java.time.temporal.ChronoField.MONTH_OF_YEAR;
import static java.time.temporal.ChronoUnit.DAYS;
import static java.time.temporal.ChronoUnit.MONTHS;
import static java.time.temporal.ChronoUnit.YEARS;

/**
 * A period expressed in terms of a standard year-month-day calendar system.
 * <p>
 * This class is used by applications seeking to handle dates in non-ISO calendar systems.
 * For example, the Japanese, Minguo, Thai Buddhist and others.
 *
 * @implSpec This class is immutable nad thread-safe.
 * @since 1.8
 */
// 时间段，包含年/月/日部件，精确到天；"日期"部件基于[非ISO]历法系统
final class ChronoPeriodImpl implements ChronoPeriod, Serializable {
    
    /*
     * this class is only used by JDK chronology implementations
     * and makes assumptions based on that fact
     */
    
    /**
     * The set of supported units.
     */
    // 当前"时间段"内包含的时间量单位
    private static final List<TemporalUnit> SUPPORTED_UNITS = List.of(YEARS, MONTHS, DAYS);
    
    /**
     * The chronology.
     */
    // 历法系统
    private final Chronology chrono;
    
    /**
     * The number of years.
     */
    final int years;   // "年"
    /**
     * The number of months.
     */
    final int months;  // "月"
    /**
     * The number of days.
     */
    final int days;    // "天"
    
    
    
    /*▼ 构造器 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Creates an instance.
     */
    ChronoPeriodImpl(Chronology chrono, int years, int months, int days) {
        Objects.requireNonNull(chrono, "chrono");
        
        this.chrono = chrono;
        this.years = years;
        this.months = months;
        this.days = days;
    }
    
    /*▲ 构造器 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 部件 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    // 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
    @Override
    public boolean isZero() {
        return years == 0 && months == 0 && days == 0;
    }
    
    // 返回当前"时间段"采用的历法系统
    @Override
    public Chronology getChronology() {
        return chrono;
    }
    
    /*▲ 部件 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 基本运算 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /*
     * 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。
     */
    @Override
    public ChronoPeriod plus(TemporalAmount amountToAdd) {
        ChronoPeriodImpl amount = validateAmount(amountToAdd);
        return new ChronoPeriodImpl(chrono, Math.addExact(years, amount.years), Math.addExact(months, amount.months), Math.addExact(days, amount.days));
    }
    
    /*
     * 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。
     */
    @Override
    public ChronoPeriod minus(TemporalAmount amountToSubtract) {
        ChronoPeriodImpl amount = validateAmount(amountToSubtract);
        
        return new ChronoPeriodImpl(chrono, Math.subtractExact(years, amount.years), Math.subtractExact(months, amount.months), Math.subtractExact(days, amount.days));
    }
    
    /*
     * 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。
     */
    @Override
    public ChronoPeriod multipliedBy(int scalar) {
        if(this.isZero() || scalar == 1) {
            return this;
        }
        
        return new ChronoPeriodImpl(chrono, Math.multiplyExact(years, scalar), Math.multiplyExact(months, scalar), Math.multiplyExact(days, scalar));
    }
    
    // 判断当前"时间段"是否为负
    @Override
    public boolean isNegative() {
        return years<0 || months<0 || days<0;
    }
    
    /*▲ 基本运算 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 增加/减少 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /*
     * 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
    public Temporal addTo(Temporal temporal) {
        validateChrono(temporal);
        if(months == 0) {
            if(years != 0) {
                temporal = temporal.plus(years, YEARS);
            }
        } else {
            long monthRange = monthRange();
            if(monthRange>0) {
                temporal = temporal.plus(years * monthRange + months, MONTHS);
            } else {
                if(years != 0) {
                    temporal = temporal.plus(years, YEARS);
                }
                temporal = temporal.plus(months, MONTHS);
            }
        }
        if(days != 0) {
            temporal = temporal.plus(days, DAYS);
        }
        return temporal;
    }
    
    /*
     * 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
    public Temporal subtractFrom(Temporal temporal) {
        validateChrono(temporal);
        if(months == 0) {
            if(years != 0) {
                temporal = temporal.minus(years, YEARS);
            }
        } else {
            long monthRange = monthRange();
            if(monthRange>0) {
                temporal = temporal.minus(years * monthRange + months, MONTHS);
            } else {
                if(years != 0) {
                    temporal = temporal.minus(years, YEARS);
                }
                temporal = temporal.minus(months, MONTHS);
            }
        }
        
        if(days != 0) {
            temporal = temporal.minus(days, DAYS);
        }
        
        return temporal;
    }
    
    /*▲ 增加/减少 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 时间量单位 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    // 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
    public List<TemporalUnit> getUnits() {
        return ChronoPeriodImpl.SUPPORTED_UNITS;
    }
    
    // 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
    public long get(TemporalUnit unit) {
        if(unit == ChronoUnit.YEARS) {
            return years;
        } else if(unit == ChronoUnit.MONTHS) {
            return months;
        } else if(unit == ChronoUnit.DAYS) {
            return days;
        } else {
            throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
        }
    }
    
    /*▲ 时间量单位 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 杂项 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    // 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
    @Override
    public ChronoPeriod normalized() {
        long monthRange = monthRange();
        if(monthRange<=0) {
            return this;
        }
        
        long totalMonths = years * monthRange + months;
        long splitYears = totalMonths / monthRange;
        int splitMonths = (int) (totalMonths % monthRange);
        if(splitYears == years && splitMonths == months) {
            return this;
        }
        
        return new ChronoPeriodImpl(chrono, Math.toIntExact(splitYears), splitMonths, days);
    }
    
    /*▲ 杂项 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    /**
     * Obtains an instance of {@code ChronoPeriodImpl} from a temporal amount.
     *
     * @param amount the temporal amount to convert, not null
     *
     * @return the period, not null
     */
    private ChronoPeriodImpl validateAmount(TemporalAmount amount) {
        Objects.requireNonNull(amount, "amount");
        
        if(!(amount instanceof ChronoPeriodImpl)) {
            throw new DateTimeException("Unable to obtain ChronoPeriod from TemporalAmount: " + amount.getClass());
        }
        
        ChronoPeriodImpl period = (ChronoPeriodImpl) amount;
        if(!chrono.equals(period.getChronology())) {
            throw new ClassCastException("Chronology mismatch, expected: " + chrono.getId() + ", actual: " + period.getChronology().getId());
        }
        
        return period;
    }
    
    /**
     * Validates that the temporal has the correct chronology.
     */
    private void validateChrono(TemporalAccessor temporal) {
        Objects.requireNonNull(temporal, "temporal");
        
        Chronology temporalChrono = temporal.query(TemporalQueries.chronology());
        
        if(temporalChrono != null && !chrono.equals(temporalChrono)) {
            throw new DateTimeException("Chronology mismatch, expected: " + chrono.getId() + ", actual: " + temporalChrono.getId());
        }
    }
    
    /**
     * Calculates the range of months.
     *
     * @return the month range, -1 if not fixed range
     */
    private long monthRange() {
        // 返回时间量字段MONTH_OF_YEAR的取值区间
        ValueRange startRange = chrono.range(MONTH_OF_YEAR);
        
        if(startRange.isFixed() && startRange.isIntValue()) {
            return startRange.getMaximum() - startRange.getMinimum() + 1;
        }
        
        return -1;
    }
    
    
    @Override
    public String toString() {
        if(isZero()) {
            return getChronology().toString() + " P0D";
        }
        
        StringBuilder buf = new StringBuilder();
        buf.append(getChronology().toString()).append(' ').append('P');
        if(years != 0) {
            buf.append(years).append('Y');
        }
        if(months != 0) {
            buf.append(months).append('M');
        }
        if(days != 0) {
            buf.append(days).append('D');
        }
        return buf.toString();
    }
    
    @Override
    public boolean equals(Object obj) {
        if(this == obj) {
            return true;
        }
        if(obj instanceof ChronoPeriodImpl) {
            ChronoPeriodImpl other = (ChronoPeriodImpl) obj;
            return years == other.years && months == other.months && days == other.days && chrono.equals(other.chrono);
        }
        return false;
    }
    
    @Override
    public int hashCode() {
        return (years + Integer.rotateLeft(months, 8) + Integer.rotateLeft(days, 16)) ^ chrono.hashCode();
    }
    
    
    
    /*▼ 序列化 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Serialization version.
     */
    private static final long serialVersionUID = 57387258289L;
    
    /**
     * Writes the Chronology using a
     * <a href="../../../serialized-form.html#java.time.chrono.Ser">dedicated serialized form</a>.
     * <pre>
     *  out.writeByte(12);  // identifies this as a ChronoPeriodImpl
     *  out.writeUTF(getId());  // the chronology
     *  out.writeInt(years);
     *  out.writeInt(months);
     *  out.writeInt(days);
     * </pre>
     *
     * @return the instance of {@code Ser}, not null
     */
    protected Object writeReplace() {
        return new Ser(Ser.CHRONO_PERIOD_TYPE, this);
    }
    
    /**
     * Defend against malicious streams.
     *
     * @param s the stream to read
     *
     * @throws InvalidObjectException always
     */
    private void readObject(ObjectInputStream s) throws ObjectStreamException {
        throw new InvalidObjectException("Deserialization via serialization delegate");
    }
    
    void writeExternal(DataOutput out) throws IOException {
        out.writeUTF(chrono.getId());
        out.writeInt(years);
        out.writeInt(months);
        out.writeInt(days);
    }
    
    static ChronoPeriodImpl readExternal(DataInput in) throws IOException {
        Chronology chrono = Chronology.of(in.readUTF());
        int years = in.readInt();
        int months = in.readInt();
        int days = in.readInt();
        return new ChronoPeriodImpl(chrono, years, months, days);
    }
    
    /*▲ 序列化 ████████████████████████████████████████████████████████████████████████████████┛ */
    
}