RegularTimePeriod.java
/* ===========================================================
* JFreeChart : a free chart library for the Java(tm) platform
* ===========================================================
*
* (C) Copyright 2000-2022, by David Gilbert and Contributors.
*
* Project Info: http://www.jfree.org/jfreechart/index.html
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This library 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 Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
* USA.
*
* [Oracle and Java are registered trademarks of Oracle and/or its affiliates.
* Other names may be trademarks of their respective owners.]
*
* ----------------------
* RegularTimePeriod.java
* ----------------------
* (C) Copyright 2001-2022, by David Gilbert.
*
* Original Author: David Gilbert;
* Contributor(s): -;
*
*/
package org.jfree.data.time;
import java.lang.reflect.Constructor;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;
import java.util.concurrent.atomic.AtomicReference;
import org.jfree.chart.date.MonthConstants;
/**
* An abstract class representing a unit of time. Convenient methods are
* provided for calculating the next and previous time periods. Conversion
* methods are defined that return the first and last milliseconds of the time
* period. The results from these methods are timezone dependent.
* <P>
* This class is immutable, and all subclasses should be immutable also.
*/
public abstract class RegularTimePeriod implements TimePeriod, Comparable,
MonthConstants {
private static final AtomicReference<Calendar> calendarPrototype = new AtomicReference<>();
private static final ThreadLocal<Calendar> threadLocalCalendar = new ThreadLocal<>();
/**
* Creates a time period that includes the specified millisecond, assuming
* the given time zone.
*
* @param c the time period class.
* @param millisecond the time.
* @param zone the time zone.
* @param locale the locale.
*
* @return The time period.
*/
public static RegularTimePeriod createInstance(Class c, Date millisecond,
TimeZone zone, Locale locale) {
RegularTimePeriod result = null;
try {
Constructor constructor = c.getDeclaredConstructor(
new Class[] {Date.class, TimeZone.class, Locale.class});
result = (RegularTimePeriod) constructor.newInstance(
new Object[] {millisecond, zone, locale});
}
catch (Exception e) {
// do nothing, so null is returned
}
return result;
}
/**
* Returns a subclass of {@link RegularTimePeriod} that is smaller than
* the specified class.
*
* @param c a subclass of {@link RegularTimePeriod}.
*
* @return A class.
*/
public static Class downsize(Class c) {
if (c.equals(Year.class)) {
return Quarter.class;
}
else if (c.equals(Quarter.class)) {
return Month.class;
}
else if (c.equals(Month.class)) {
return Day.class;
}
else if (c.equals(Day.class)) {
return Hour.class;
}
else if (c.equals(Hour.class)) {
return Minute.class;
}
else if (c.equals(Minute.class)) {
return Second.class;
}
else if (c.equals(Second.class)) {
return Millisecond.class;
}
else {
return Millisecond.class;
}
}
/**
* Creates or returns a thread-local Calendar instance.
* This function is used by the various subclasses to obtain a calendar for
* date-time to/from ms-since-epoch conversions (and to determine
* the first day of the week, in case of {@link Week}).
* <p>
* If a thread-local calendar was set with {@link #setThreadLocalCalendarInstance(Calendar)},
* then it is simply returned.
* <p>
* Otherwise, If a global calendar prototype was set with {@link #setCalendarInstancePrototype(Calendar)},
* then it is cloned and set as the thread-local calendar instance for future use,
* as if it was set with {@link #setThreadLocalCalendarInstance(Calendar)}.
* <p>
* Otherwise, if neither is set, a new instance will be created every
* time with {@link Calendar#getInstance()}, resorting to JFreeChart 1.5.0
* behavior (leading to huge load on GC and high memory consumption
* if many instances are created).
*
* @return a thread-local Calendar instance
*/
protected static Calendar getCalendarInstance() {
Calendar calendar = threadLocalCalendar.get();
if (calendar == null) {
Calendar prototype = calendarPrototype.get();
if (prototype != null) {
calendar = (Calendar) prototype.clone();
threadLocalCalendar.set(calendar);
}
}
return calendar != null ? calendar : Calendar.getInstance();
}
/**
* Sets the thread-local calendar instance for time calculations.
* <p>
* {@code RegularTimePeriod} instances sometimes need a {@link Calendar}
* to perform time calculations (date-time from/to milliseconds-since-epoch).
* In JFreeChart 1.5.0, they created a new {@code Calendar} instance
* every time they needed one. This created a huge load on GC and lead
* to high memory consumption. To avoid this, a thread-local {@code Calendar}
* instance can be set, which will then be used for time calculations
* every time, unless the caller passes a specific {@code Calendar}
* instance in places where the API allows it.
* <p>
* If the specified calendar is {@code null}, or if this method was never called,
* then the next time a calendar instance is needed, a new one will be created by cloning
* the global prototype set with {@link #setCalendarInstancePrototype(Calendar)}.
* If none was set either, then a new instance will be created every time
* with {@link Calendar#getInstance()}, resorting to JFreeChart 1.5.0 behavior.
*
* @param calendar the new thread-local calendar instance
*/
public static void setThreadLocalCalendarInstance(Calendar calendar) {
threadLocalCalendar.set(calendar);
}
/**
* Sets a global calendar prototype for time calculations.
* <p>
* {@code RegularTimePeriod} instances sometimes need a {@link Calendar}
* to perform time calculations (date-time from/to milliseconds-since-epoch).
* In JFreeChart 1.5.0, they created a new {@code Calendar} instance
* every time they needed one. This created a huge load on GC and lead
* to high memory consumption. To avoid this, a prototype {@code Calendar}
* can be set, which will be then cloned by every thread that needs
* a {@code Calendar} instance. The prototype is not cloned right away,
* and stored instead for later cloning, therefore the caller must not
* alter the prototype after it has been passed to this method.
* <p>
* If the prototype is {@code null}, then thread-local calendars
* set with {@link #setThreadLocalCalendarInstance(Calendar)} will be
* used instead. If none was set for some thread, then a new instance will be
* created with {@link Calendar#getInstance()} every time one is needed.
* However, if the prototype was already cloned by some thread,
* then setting it to {@code null} has no effect, and that thread must
* explicitly set its own instance to {@code null} or something else to get
* rid of the cloned calendar.
* <p>
* Calling {@code setCalendarInstancePrototype(Calendar.getInstance())}
* somewhere early in an application will effectively mimic JFreeChart
* 1.5.0 behavior (using the default calendar everywhere unless explicitly
* specified), while preventing the many-allocations problem. There is one
* important caveat, however: once a prototype is cloned by some
* thread, calling {@link TimeZone#setDefault(TimeZone)}
* or {@link Locale#setDefault(Locale)}} will have no
* effect on future calculations. To avoid this problem, simply set
* the default time zone and locale before setting the prototype.
*
* @param calendar the new thread-local calendar instance
*/
public static void setCalendarInstancePrototype(Calendar calendar) {
calendarPrototype.set(calendar);
}
/**
* Returns the time period preceding this one, or {@code null} if some
* lower limit has been reached.
*
* @return The previous time period (possibly {@code null}).
*/
public abstract RegularTimePeriod previous();
/**
* Returns the time period following this one, or {@code null} if some
* limit has been reached.
*
* @return The next time period (possibly {@code null}).
*/
public abstract RegularTimePeriod next();
/**
* Returns a serial index number for the time unit.
*
* @return The serial index number.
*/
public abstract long getSerialIndex();
//////////////////////////////////////////////////////////////////////////
/**
* Recalculates the start date/time and end date/time for this time period
* relative to the supplied calendar (which incorporates a time zone).
*
* @param calendar the calendar ({@code null} not permitted).
*
* @since 1.0.3
*/
public abstract void peg(Calendar calendar);
/**
* Returns the date/time that marks the start of the time period. This
* method returns a new {@code Date} instance every time it is called.
*
* @return The start date/time.
*
* @see #getFirstMillisecond()
*/
@Override
public Date getStart() {
return new Date(getFirstMillisecond());
}
/**
* Returns the date/time that marks the end of the time period. This
* method returns a new {@code Date} instance every time it is called.
*
* @return The end date/time.
*
* @see #getLastMillisecond()
*/
@Override
public Date getEnd() {
return new Date(getLastMillisecond());
}
/**
* Returns the first millisecond of the time period. This will be
* determined relative to the time zone specified in the constructor, or
* in the calendar instance passed in the most recent call to the
* {@link #peg(Calendar)} method.
*
* @return The first millisecond of the time period.
*
* @see #getLastMillisecond()
*/
public abstract long getFirstMillisecond();
/**
* Returns the first millisecond of the time period, evaluated using the
* supplied calendar (which incorporates a timezone).
*
* @param calendar the calendar ({@code null} not permitted).
*
* @return The first millisecond of the time period.
*
* @throws NullPointerException if {@code calendar} is {@code null}.
*
* @see #getLastMillisecond(Calendar)
*/
public abstract long getFirstMillisecond(Calendar calendar);
/**
* Returns the last millisecond of the time period. This will be
* determined relative to the time zone specified in the constructor, or
* in the calendar instance passed in the most recent call to the
* {@link #peg(Calendar)} method.
*
* @return The last millisecond of the time period.
*
* @see #getFirstMillisecond()
*/
public abstract long getLastMillisecond();
/**
* Returns the last millisecond of the time period, evaluated using the
* supplied calendar (which incorporates a timezone).
*
* @param calendar the calendar ({@code null} not permitted).
*
* @return The last millisecond of the time period.
*
* @see #getFirstMillisecond(Calendar)
*/
public abstract long getLastMillisecond(Calendar calendar);
/**
* Returns the millisecond closest to the middle of the time period.
*
* @return The middle millisecond.
*/
public long getMiddleMillisecond() {
long m1 = getFirstMillisecond();
long m2 = getLastMillisecond();
return m1 + (m2 - m1) / 2;
}
/**
* Returns the millisecond closest to the middle of the time period,
* evaluated using the supplied calendar (which incorporates a timezone).
*
* @param calendar the calendar.
*
* @return The middle millisecond.
*/
public long getMiddleMillisecond(Calendar calendar) {
long m1 = getFirstMillisecond(calendar);
long m2 = getLastMillisecond(calendar);
return m1 + (m2 - m1) / 2;
}
/**
* Returns the millisecond (relative to the epoch) corresponding to the
* specified {@code anchor} using the supplied {@code calendar}
* (which incorporates a time zone).
*
* @param anchor the anchor ({@code null} not permitted).
* @param calendar the calendar ({@code null} not permitted).
*
* @return Milliseconds since the epoch.
*
* @since 1.0.18
*/
public long getMillisecond(TimePeriodAnchor anchor, Calendar calendar) {
if (anchor.equals(TimePeriodAnchor.START)) {
return getFirstMillisecond(calendar);
} else if (anchor.equals(TimePeriodAnchor.MIDDLE)) {
return getMiddleMillisecond(calendar);
} else if (anchor.equals(TimePeriodAnchor.END)) {
return getLastMillisecond(calendar);
} else {
throw new IllegalStateException("Unrecognised anchor: " + anchor);
}
}
/**
* Returns a string representation of the time period.
*
* @return The string.
*/
@Override
public String toString() {
return String.valueOf(getStart());
}
}