Date operations in Java already passed or near in the future

Question

In Java (I'm a junior) - how do you perform various date operations?

Assess "storedDate is one week away from today" and "storedDate has passed"

I am not sure if its the best approach or how to do the condition check

java.sql.Date  dueDate = (Date) loggedUser.get("dueDate");

I've seen various calculations like this - but not sure an if condition could be met like this?

Calendar c= Calendar.getInstance();
//c.set(Calendar.DAY_OF_WEEK,Calendar.SUNDAY);
c.set(Calendar.HOUR_OF_DAY,0);
c.set(Calendar.MINUTE,0);
c.set(Calendar.SECOND,0);
DateFormat df=new SimpleDateFormat("EEE yyyy/MM/dd HH:mm:ss");
System.out.println(df.format(c.getTime()));// This past Sunday [ May include today ]
c.add(Calendar.DATE,7);
System.out.println(df.format(c.getTime()));// Next Sunday

Answer 1

Step 1: Learn to read API pages. Here is the Calendar API Page, read it.

For your class project, you don't care about timezone (since you didn't mention it in your post).

Get a date parameter: public void methodName(Date dateParameter)

Create a Calendar containing now: Calendar myCalendar = Calendar.getInstance();

Set a calendar to a date value: myCalendar.setTime(dateParameter)

"Calculate" one week from today: myCalendar.roll(Calendar.DAY_OF_YEAR, 7)

The Calendar object stores Millisecond, Second, Minute, and Hour. Clear these using the set method.

Compare Calendar objects using the after method.

Answer 2

tl;dr

LocalDate.now( ZoneId.of( "Pacific/Auckland" ) )
.with( 
    TemporalAdjusters.previousOrSame​( DayOfWeek.SUNDAY ) 
)

java.time

The modern approach uses java.time classes.

Get current moment in UTC.

Instant instant = Instant.now() ; 

If you care about day-of-week, you care about date. Determining a date requires a time zone. For any given moment the date varies around the globe by zone.

ZoneId z = ZoneId.of( "Africa/Tunis" ) ;
ZonedDateTime zdt = instant.atZone( z ) ;  // Same point on the timeline, different wall-clock time.

To focus on date-only without time-of-day, extract a LocalDate.

LocalDate ld = zdt.toLocalDate() ;

To adjust into other moments, use a TemporalAdjuster. Find implementations in TemporalAdjusters.

LocalDate previousOrSameSunday = ld.with( 
    TemporalAdjusters.previousOrSame​( DayOfWeek.SUNDAY ) 
) ;

…and…

LocalDate nextOrSameSunday = ld.with( 
    TemporalAdjusters.nextOrSame​( DayOfWeek.SUNDAY ) 
) ;

To compare, look for isBefore, isAfter, isEqual, and equals methods on the various java.time classes.

thisLocalDate.isBefore( thatLocalDate) 

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About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
  • See How to use ThreeTenABP….

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.