根据经纬度和当前日期获取当地的日出日落时间，强大的Google搜索让我迅速找到了一个外国人写的一个java类，代码中的注释写得很清楚。
这里直接贴出代码来：
/******************************************************************************
*
* SunriseSunset.java
*
*******************************************************************************
*
* Java Class: SunriseSunset
*
* This Java class is part of a collection of classes developed for the
* reading and processing of oceanographic and meterological data collected
* since 1970 by environmental buoys and stations. This dataset is
* maintained by the National Oceanographic Data Center and is publicly
* available. These Java classes were written for the US Environmental
* Protection Agency's National Exposure Research Laboratory under Contract
* No. GS-10F-0073K with Neptune and Company of Los Alamos, New Mexico.
*
* Purpose:
*
* This Java class performs calculations to determine the time of
* sunrise and sunset given lat, long, and date.
*
* Inputs:
*
* Latitude, longitude, date/time, and time zone.
*
* Outputs:
*
* Local time of sunrise and sunset as calculated by the
* program.
* If no sunrise or no sunset occurs, or if the sun is up all day
* or down all day, appropriate boolean values are set.
* A boolean is provided to identify if the time provided is during the day.
*
* The above values are accessed by the following methods:
*
* Date getSunrise() returns date/time of sunrise
* Date getSunset() returns date/time of sunset
* boolean isSunrise() returns true if there was a sunrise, else false
* boolean isSunset() returns true if there was a sunset, else false
* boolean isSunUp() returns true if sun is up all day, else false
* boolean isSunDown() returns true if sun is down all day, else false
* boolean isDaytime() returns true if sun is up at the time
* specified, else false
*
* Required classes from the Java library:
*
* java.util.Date
* java.text.SimpleDateFormat
* java.text.ParseException;
* java.math.BigDecimal;
*
* Package of which this class is a member:
*
* default
*
* Known limitations:
*
* It is assumed that the data provided are within valie ranges
* (i.e. latitude between -90 and +90, longitude between 0 and 360,
* a valid date, and time zone between -14 and +14.
*
* Compatibility:
*
* Java 1.1.8
*
* References:
*
* The mathematical algorithms used in this program are patterned
* after those debveloped by Roger Sinnott in his BASIC program,
* SUNUP.BAS, published in Sky & Telescope magazine:
* Sinnott, Roger W. "Sunrise and Sunset: A Challenge"
* Sky & Telescope, August, 1994 p.84-85
*
* The following is a cross-index of variables used in SUNUP.BAS.
* A single definition from multiple reuse of variable names in
* SUNUP.BAS was clarified with various definitions in this program.
*
* SUNUP.BAS this class
*
* A dfA
* A(2) dfAA1, dfAA2
* A0 dfA0
* A2 dfA2
* A5 dfA5
* AZ Not used
* C dfCosLat
* C0 dfC0
* D iDay
* D(2) dfDD1, dfDD2
* D0 dfD0
* D1 dfD1
* D2 dfD2
* D5 dfD5
* D7 Not used
* DA dfDA
* DD dfDD
* G bGregorian, dfGG
* H dfTimeZone
* H0 dfH0
* H1 dfH1
* H2 dfH2
* H3 dfHourRise, dfHourSet
* H7 Not used
* J dfJ
* J3 dfJ3
* K1 dfK1
* L dfLL
* L0 dfL0
* L2 dfL2
* L5 dfLon
* M iMonth
* M3 dfMinRise, dfMinSet
* N7 Not used
* P dfP
* S iSign, dfSinLat, dfSS
* T dfT
* T0 dfT0
* T3 not used
* TT dfTT
* U dfUU
* V dfVV
* V0 dfV0
* V1 dfV1
* V2 dfV2
* W dfWW
* Y iYear
* Z dfZenith
* Z0 dfTimeZone
*
*
* Author/Company:
*
* JDT: John Tauxe, Neptune and Company
* JMG: Jo Marie Green
*
* Change log:
*
* date ver by description of change
* _________ _____ ___ ______________________________________________
* 5 Jan 01 0.006 JDT Excised from ssapp.java v. 0.005.
* 11 Jan 01 0.007 JDT Minor modifications to comments based on
* material from Sinnott, 1994.
* 7 Feb 01 0.008 JDT Fixed backwards time zone. The standard is that
* local time zone is specified in hours EAST of
* Greenwich, so that EST would be -5, for example.
* For some reason, SUNUP.BAS does this backwards
* (probably an americocentric perspective) and
* SunriseSunset adopted that convention. Oops.
* So the sign in the math is changed.
* 7 Feb 01 0.009 JDT Well, that threw off the azimuth calculation...
* Removed the azimuth calculations.
* 14 Feb 01 0.010 JDT Added ability to accept a time (HH:mm) in
* dateInput, and decide if that time is daytime
* or nighttime.
* 27 Feb 01 0.011 JDT Added accessor methods in place of having public
* variables to get results.
* 28 Feb 01 0.012 JDT Cleaned up list of imported classes.
* 28 Mar 01 1.10 JDT Final version accompanying deliverable 1b.
* 4 Apr 01 1.11 JDT Moved logic supporting .isDaytime into method.
* Moved calculations out of constructor.
* 01 May 01 1.12 JMG Added 'GMT' designation and testing lines.
* 16 May 01 1.13 JDT Added setLenient( false ) and setTimeZone( tz )
* to dfmtDay, dfmtMonth, and dfmtYear in
* doCalculations.
* 27 Jun 01 1.14 JDT Removed reliance on StationConstants (GMT).
* 13 Aug 01 1.20 JDT Final version accompanying deliverable 1c.
* 6 Sep 01 1.21 JDT Thorough code and comment review.
* 21 Sep 01 1.30 JDT Final version accompanying deliverable 2.
* 17 Dec 01 1.40 JDT Version accompanying final deliverable.
*
*----------------------------------------------------------------------------*/
// Import required classes and packages
import java.util.Date;
import java.text.SimpleDateFormat;
import java.text.ParseException;
import java.math.BigDecimal;
import java.util.TimeZone;
/******************************************************************************
* class: SunriseSunset class
*******************************************************************************
*
* This Java class performs calculations to determine the time of
* sunrise and sunset given lat, long, and date.
*
* It is assumed that the data provided are within valie ranges
* (i.e. latitude between -90 and +90, longitude between 0 and 360,
* a valid date, and time zone between -14 and +14.
*
*----------------------------------------------------------------------------*/
public class SunriseSunset
{
// Declare and initialize variables
private double dfLat; // latitude from user
private double dfLon; // latitude from user
private Date dateInput; // date/time from user
private double dfTimeZone; // time zone from user
private Date dateSunrise; // date and time of sunrise
private Date dateSunset; // date and time of sunset
private boolean bSunriseToday = false; // flag for sunrise on this date
private boolean bSunsetToday = false; // flag for sunset on this date
private boolean bSunUpAllDay = false; // flag for sun up all day
private boolean bSunDownAllDay = false; // flag for sun down all day
private boolean bDaytime = false; // flag for daytime, given
// hour and min in dateInput
private boolean bSunrise = false; // sunrise during hour checked
private boolean bSunset = false; // sunset during hour checked
private boolean bGregorian = false; // flag for Gregorian calendar
private int iJulian; // Julian day
private int iYear; // year of date of interest
private int iMonth; // month of date of interest
private int iDay; // day of date of interest
private int iCount; // a simple counter
private int iSign; // SUNUP.BAS: S
private double dfHourRise, dfHourSet; // hour of event: SUNUP.BAS H3
private double dfMinRise, dfMinSet; // minute of event: SUNUP.BAS M3
private double dfSinLat, dfCosLat; // sin and cos of latitude
private double dfZenith; // SUNUP.BAS Z: Zenith
private SimpleDateFormat dfmtDate; // formatting for date alone
private SimpleDateFormat dfmtDateTime; // formatting for date and time
private SimpleDateFormat dfmtYear; // formatting for year
private SimpleDateFormat dfmtMonth; // formatting for month
private SimpleDateFormat dfmtDay; // formatting for day
// Many variables in SUNUP.BAS have undocumented meanings,
// and so are translated rather directly to avoid confusion:
private double dfAA1 = 0, dfAA2 = 0; // SUNUP.BAS A(2)
private double dfDD1 = 0, dfDD2 = 0; // SUNUP.BAS D(2)
private double dfC0; // SUNUP.BAS C0
private double dfK1; // SUNUP.BAS K1
private double dfP; // SUNUP.BAS P
private double dfJ; // SUNUP.BAS J
private double dfJ3; // SUNUP.BAS J3
private double dfA; // SUNUP.BAS A
private double dfA0, dfA2, dfA5; // SUNUP.BAS A0, A2, A5
private double dfD0, dfD1, dfD2, dfD5; // SUNUP.BAS D0, D1, D2, D5
private double dfDA, dfDD; // SUNUP.BAS DA, DD
private double dfH0, dfH1, dfH2; // SUNUP.BAS H0, H1, H2
private double dfL0, dfL2; // SUNUP.BAS L0, L2
private double dfT, dfT0, dfTT; // SUNUP.BAS T, T0, TT
private double dfV0, dfV1, dfV2; // SUNUP.BAS V0, V1, V2
private TimeZone tz = TimeZone.getTimeZone( "GMT" );
/******************************************************************************
* method: SunriseSunset
*******************************************************************************
*
* Constructor for SunriseSunset class.
*
*----------------------------------------------------------------------------*/
SunriseSunset(
double dfLatIn, // latitude
double dfLonIn, // longitude
Date dateInputIn, // date
double dfTimeZoneIn // time zone
)
{
// Copy values supplied as agruments to local variables.
dfLat = dfLatIn;
dfLon = dfLonIn;
dateInput = dateInputIn;
dfTimeZone = dfTimeZoneIn;
// Call the method to do the calculations.
doCalculations();
} // end of class constructor
/******************************************************************************
* method: doCalculations
*******************************************************************************
*
* Method for performing the calculations done in SUNUP.BAS.
*
*----------------------------------------------------------------------------*/
private void doCalculations()
{
try
{
// Break out day, month, and year from date provided.
// (This is necesary for the math algorithms.)
dfmtYear = new SimpleDateFormat( "yyyy" );
dfmtYear.setLenient( false );
dfmtYear.setTimeZone( tz );
dfmtMonth = new SimpleDateFormat( "M" );
dfmtMonth.setLenient( false );
dfmtMonth.setTimeZone( tz );
dfmtDay = new SimpleDateFormat( "d" );
dfmtDay.setLenient( false );
dfmtDay.setTimeZone( tz );
iYear = Integer.parseInt( dfmtYear.format( dateInput ) );
iMonth = Integer.parseInt( dfmtMonth.format( dateInput ) );
iDay = Integer.parseInt( dfmtDay.format( dateInput ) );
// Convert time zone hours to decimal days (SUNUP.BAS line 50)
dfTimeZone = dfTimeZone / 24.0;
// NOTE: (7 Feb 2001) Here is a non-standard part of SUNUP.BAS:
// It (and this algorithm) assumes that the time zone is
// positive west, instead of the standard negative west.
// Classes calling SunriseSunset will be assuming that
// times zones are specified in negative west, so here the
// sign is changed so that the SUNUP algorithm works:
dfTimeZone = -dfTimeZone;
// Convert longitude to fraction (SUNUP.BAS line 50)
dfLon = dfLon / 360.0;
// Convert calendar date to Julian date:
// Check to see if it's later than 1583: Gregorian calendar
// When declared, bGregorian is initialized to false.
// ** Consider making a separate class of this function. **
if( iYear >= 1583 ) bGregorian = true;
// SUNUP.BAS 1210
dfJ = -Math.floor( 7.0 // SUNUP used INT, not floor
* ( Math.floor(
( iMonth + 9.0 )
/ 12.0
) + iYear
) / 4.0
)
// add SUNUP.BAS 1240 and 1250 for G = 0
+ Math.floor( iMonth * 275.0 / 9.0 )
+ iDay
+ 1721027.0
+ iYear * 367.0;
if ( bGregorian )
{
// SUNUP.BAS 1230
if ( ( iMonth - 9.0 ) < 0.0 ) iSign = -1;
else iSign = 1;
dfA = Math.abs( iMonth - 9.0 );
// SUNUP.BAS 1240 and 1250
dfJ3 = -Math.floor(
(
Math.floor(
Math.floor( iYear
+ (double)iSign
* Math.floor( dfA / 7.0 )
)
/ 100.0
) + 1.0
) * 0.75
);
// correct dfJ as in SUNUP.BAS 1240 and 1250 for G = 1
dfJ = dfJ + dfJ3 + 2.0;
}
// SUNUP.BAS 1290
iJulian = (int)dfJ - 1;
// SUNUP.BAS 60 and 70 (see also line 1290)
dfT = (double)iJulian - 2451545.0 + 0.5;
dfTT = dfT / 36525.0 + 1.0; // centuries since 1900
// Calculate local sidereal time at 0h in zone time
// SUNUP.BAS 410 through 460
dfT0 = ( dfT * 8640184.813 / 36525.0
+ 24110.5
+ dfTimeZone * 86636.6
+ dfLon * 86400.0
)
/ 86400.0;
dfT0 = dfT0 - Math.floor( dfT0 ); // NOTE: SUNUP.BAS uses INT()
dfT0 = dfT0 * 2.0 * Math.PI;
// SUNUP.BAS 90
dfT = dfT + dfTimeZone;
// SUNUP.BAS 110: Get Sun's position
for( iCount=0; iCount<=1; iCount++ ) // Loop thru only twice
{
// Calculate Sun's right ascension and declination
// at the start and end of each day.
// SUNUP.BAS 910 - 1160: Fundamental arguments
// from van Flandern and Pulkkinen, 1979
// declare local temporary doubles for calculations
double dfGG; // SUNUP.BAS G
double dfLL; // SUNUP.BAS L
double dfSS; // SUNUP.BAS S
double dfUU; // SUNUP.BAS U
double dfVV; // SUNUP.BAS V
double dfWW; // SUNUP.BAS W
dfLL = 0.779072 + 0.00273790931 * dfT;
dfLL = dfLL - Math.floor( dfLL );
dfLL = dfLL * 2.0 * Math.PI;
dfGG = 0.993126 + 0.0027377785 * dfT;
dfGG = dfGG - Math.floor( dfGG );
dfGG = dfGG * 2.0 * Math.PI;
dfVV = 0.39785 * Math.sin( dfLL )
- 0.01000 * Math.sin( dfLL - dfGG )
+ 0.00333 * Math.sin( dfLL + dfGG )
- 0.00021 * Math.sin( dfLL ) * dfTT;
dfUU = 1
- 0.03349 * Math.cos( dfGG )
- 0.00014 * Math.cos( dfLL * 2.0 )
+ 0.00008 * Math.cos( dfLL );
dfWW = - 0.00010
- 0.04129 * Math.sin( dfLL * 2.0 )
+ 0.03211 * Math.sin( dfGG )
- 0.00104 * Math.sin( 2.0 * dfLL - dfGG )
- 0.00035 * Math.sin( 2.0 * dfLL + dfGG )
- 0.00008 * Math.sin( dfGG ) * dfTT;
// Compute Sun's RA and Dec; SUNUP.BAS 1120 - 1140
dfSS = dfWW / Math.sqrt( dfUU - dfVV * dfVV );
dfA5 = dfLL
+ Math.atan( dfSS / Math.sqrt( 1.0 - dfSS * dfSS ));
dfSS = dfVV / Math.sqrt( dfUU );
dfD5 = Math.atan( dfSS / Math.sqrt( 1 - dfSS * dfSS ));
// Set values and increment t
if ( iCount == 0 ) // SUNUP.BAS 125
{
dfAA1 = dfA5;
dfDD1 = dfD5;
}
else // SUNUP.BAS 145
{
dfAA2 = dfA5;
dfDD2 = dfD5;
}
dfT = dfT + 1.0; // SUNUP.BAS 130
} // end of Get Sun's Position for loop
if ( dfAA2 < dfAA1 ) dfAA2 = dfAA2 + 2.0 * Math.PI;
// SUNUP.BAS 150
dfZenith = Math.PI * 90.833 / 180.0; // SUNUP.BAS 160
dfSinLat = Math.sin( dfLat * Math.PI / 180.0 ); // SUNUP.BAS 170
dfCosLat = Math.cos( dfLat * Math.PI / 180.0 ); // SUNUP.BAS 170
dfA0 = dfAA1; // SUNUP.BAS 190
dfD0 = dfDD1; // SUNUP.BAS 190
dfDA = dfAA2 - dfAA1; // SUNUP.BAS 200
dfDD = dfDD2 - dfDD1; // SUNUP.BAS 200
dfK1 = 15.0 * 1.0027379 * Math.PI / 180.0; // SUNUP.BAS 330
// Initialize sunrise and sunset times, and other variables
// hr and min are set to impossible times to make errors obvious
dfHourRise = 99.0;
dfMinRise = 99.0;
dfHourSet = 99.0;
dfMinSet = 99.0;
dfV0 = 0.0; // initialization implied by absence in SUNUP.BAS
dfV2 = 0.0; // initialization implied by absence in SUNUP.BAS
// Test each hour to see if the Sun crosses the horizon
// and which way it is heading.
for( iCount=0; iCount<24; iCount++ ) // SUNUP.BAS 210
{
double tempA; // SUNUP.BAS A
double tempB; // SUNUP.BAS B
double tempD; // SUNUP.BAS D
double tempE; // SUNUP.BAS E
dfC0 = (double)iCount;
dfP = ( dfC0 + 1.0 ) / 24.0; // SUNUP.BAS 220
dfA2 = dfAA1 + dfP * dfDA; // SUNUP.BAS 230
dfD2 = dfDD1 + dfP * dfDD; // SUNUP.BAS 230
dfL0 = dfT0 + dfC0 * dfK1; // SUNUP.BAS 500
dfL2 = dfL0 + dfK1; // SUNUP.BAS 500
dfH0 = dfL0 - dfA0; // SUNUP.BAS 510
dfH2 = dfL2 - dfA2; // SUNUP.BAS 510
// hour angle at half hour
dfH1 = ( dfH2 + dfH0 ) / 2.0; // SUNUP.BAS 520
// declination at half hour
dfD1 = ( dfD2 + dfD0 ) / 2.0; // SUNUP.BAS 530
// Set value of dfV0 only if this is the first hour,
// otherwise, it will get set to the last dfV2 (SUNUP.BAS 250)
if ( iCount == 0 ) // SUNUP.BAS 550
{
dfV0 = dfSinLat * Math.sin( dfD0 )
+ dfCosLat * Math.cos( dfD0 ) * Math.cos( dfH0 )
- Math.cos( dfZenith ); // SUNUP.BAS 560
}
else
dfV0 = dfV2; // That is, dfV2 from the previous hour.
dfV2 = dfSinLat * Math.sin( dfD2 )
+ dfCosLat * Math.cos( dfD2 ) * Math.cos( dfH2 )
- Math.cos( dfZenith ); // SUNUP.BAS 570
// if dfV0 and dfV2 have the same sign, then proceed to next hr
if (
( dfV0 >= 0.0 && dfV2 >= 0.0 ) // both are positive
|| // or
( dfV0 < 0.0 && dfV2 < 0.0 ) // both are negative
)
{
// Break iteration and proceed to test next hour
dfA0 = dfA2; // SUNUP.BAS 250
dfD0 = dfD2; // SUNUP.BAS 250
continue; // SUNUP.BAS 610
}
dfV1 = dfSinLat * Math.sin( dfD1 )
+ dfCosLat * Math.cos( dfD1 ) * Math.cos( dfH1 )
- Math.cos( dfZenith ); // SUNUP.BAS 590
tempA = 2.0 * dfV2 - 4.0 * dfV1 + 2.0 * dfV0;
// SUNUP.BAS 600
tempB = 4.0 * dfV1 - 3.0 * dfV0 - dfV2; // SUNUP.BAS 600
tempD = tempB * tempB - 4.0 * tempA * dfV0; // SUNUP.BAS 610
if ( tempD < 0.0 )
{
// Break iteration and proceed to test next hour
dfA0 = dfA2; // SUNUP.BAS 250
dfD0 = dfD2; // SUNUP.BAS 250
continue; // SUNUP.BAS 610
}
tempD = Math.sqrt( tempD ); // SUNUP.BAS 620
// Determine occurence of sunrise or sunset.
// Flags to identify occurrence during this day are
// bSunriseToday and bSunsetToday, and are initialized false.
// These are set true only if sunrise or sunset occurs
// at any point in the hourly loop. Never set to false.
// Flags to identify occurrence during this hour:
bSunrise = false; // reset before test
bSunset = false; // reset before test
if ( dfV0 < 0.0 && dfV2 > 0.0 ) // sunrise occurs this hour
{
bSunrise = true; // SUNUP.BAS 640
bSunriseToday = true; // sunrise occurred today
}
if ( dfV0 > 0.0 && dfV2 < 0.0 ) // sunset occurs this hour
{
bSunset = true; // SUNUP.BAS 660
bSunsetToday = true; // sunset occurred today
}
tempE = ( tempD - tempB ) / ( 2.0 * tempA );
if ( tempE > 1.0 || tempE < 0.0 ) // SUNUP.BAS 670, 680
tempE = ( -tempD - tempB ) / ( 2.0 * tempA );
// Set values of hour and minute of sunset or sunrise
// only if sunrise/set occurred this hour.
if ( bSunrise )
{
dfHourRise = Math.floor( dfC0 + tempE + 1.0/120.0 );
dfMinRise = Math.floor(
( dfC0 + tempE + 1.0/120.0
- dfHourRise
)
* 60.0
);
}
if ( bSunset )
{
dfHourSet = Math.floor( dfC0 + tempE + 1.0/120.0 );
dfMinSet = Math.floor(
( dfC0 + tempE + 1.0/120.0
- dfHourSet
)
* 60.0
);
}
// Change settings of variables for next loop
dfA0 = dfA2; // SUNUP.BAS 250
dfD0 = dfD2; // SUNUP.BAS 250
} // end of loop testing each hour for an event
// After having checked all hours, set flags if no rise or set
// bSunUpAllDay and bSundownAllDay are initialized as false
if ( !bSunriseToday && !bSunsetToday )
{
if ( dfV2 < 0.0 )
bSunDownAllDay = true;
else
bSunUpAllDay = true;
}
// Load dateSunrise with data
dfmtDateTime = new SimpleDateFormat( "d M yyyy HH:mm z" );
if( bSunriseToday )
{
dateSunrise = dfmtDateTime.parse( iDay
+ " " + iMonth
+ " " + iYear
+ " " + (int)dfHourRise
+ ":" + (int)dfMinRise
+ " GMT" );
}
// Load dateSunset with data
if( bSunsetToday )
{
dateSunset = dfmtDateTime.parse( iDay
+ " " + iMonth
+ " " + iYear
+ " " + (int)dfHourSet
+ ":" + (int)dfMinSet
+ " GMT" );
}
} // end of try
// Catch errors
catch( ParseException e )
{
System.out.println( "\nCannot parse date" );
System.out.println( e );
System.exit( 1 );
} // end of catch
}
/******************************************************************************
* method: getSunrise()
*******************************************************************************
*
* Gets the date and time of sunrise. If there is no sunrise, returns null.
*
* Member of SunriseSunset class
*
* -------------------------------------------------------------------------- */
public Date getSunrise()
{
if ( bSunriseToday )
return( dateSunrise );
else
return( null );
}
/******************************************************************************
* method: getSunset()
*******************************************************************************
*
* Gets the date and time of sunset. If there is no sunset, returns null.
*
* Member of SunriseSunset class
*
* -------------------------------------------------------------------------- */
public Date getSunset()
{
if ( bSunsetToday )
return( dateSunset );
else
return( null );
}
/******************************************************************************
* method: isSunrise()
*******************************************************************************
*
* Returns a boolean identifying if there was a sunrise.
*
* Member of SunriseSunset class
*
* -------------------------------------------------------------------------- */
public boolean isSunrise()
{
return( bSunriseToday );
}
/******************************************************************************
* method: isSunset()
*******************************************************************************
*
* Returns a boolean identifying if there was a sunset.
*
* Member of SunriseSunset class
*
* -------------------------------------------------------------------------- */
public boolean isSunset()
{
return( bSunsetToday );
}
/******************************************************************************
* method: isSunUp()
*******************************************************************************
*
* Returns a boolean identifying if the sun is up all day.
*
* Member of SunriseSunset class
*
* -------------------------------------------------------------------------- */
public boolean isSunUp()
{
return( bSunUpAllDay );
}
/******************************************************************************
* method: isSunDown()
*******************************************************************************
*
* Returns a boolean identifying if the sun is down all day.
*
* Member of SunriseSunset class
*
* -------------------------------------------------------------------------- */
public boolean isSunDown()
{
return( bSunDownAllDay );
}
/******************************************************************************
* method: isDaytime()
*******************************************************************************
*
* Returns a boolean identifying if it is daytime at the hour contained in
* the Date object passed to SunriseSunset on construction.
*
* Member of SunriseSunset class
*
* -------------------------------------------------------------------------- */
public boolean isDaytime()
{
// Determine if it is daytime (at sunrise or later)
// or nighttime (at sunset or later) at the location of interest
// but expressed in the time zone requested.
if ( bSunriseToday && bSunsetToday ) // sunrise and sunset
{
if ( dateSunrise.before( dateSunset ) ) // sunrise < sunset
{
if (
(
dateInput.after( dateSunrise )
dateInput.equals( dateSunrise )
)
&&
dateInput.before( dateSunset )
)
bDaytime = true;
else
bDaytime = false;
}
else // sunrise comes after sunset (in opposite time zones)
{
if (
(
dateInput.after( dateSunrise )
dateInput.equals( dateSunrise )
)
|| // use OR rather than AND
dateInput.before( dateSunset )
)
bDaytime = true;
else
bDaytime = false;
}
}
else if ( bSunUpAllDay ) // sun is up all day
bDaytime = true;
else if ( bSunDownAllDay ) // sun is down all day
bDaytime = false;
else if ( bSunriseToday ) // sunrise but no sunset
{
if ( dateInput.before( dateSunrise ) )
bDaytime = false;
else
bDaytime = true;
}
else if ( bSunsetToday ) // sunset but no sunrise
{
if ( dateInput.before( dateSunset ) )
bDaytime = true;
else
bDaytime = false;
}
else bDaytime = false; // this should never execute
return( bDaytime );
}
} // end of class
/*-----------------------------------------------------------------------------
* end of class
*----------------------------------------------------------------------------*/