How to check a timeperiod is overlapping another time period in java

Question

How to check a time period is overlapping another time period in the same day.

For example,

1. 7:00AM to 10:30AM is overlapping 10:00AM to 11:30AM
2. 7:00AM to 10:30AM is overlapping 8:00AM to 9:00AM
3. 7:00AM to 10:30AM is overlapping 5:00AM to 8:00AM

Answer 1

There is a simple solution, expressed here as a utility method:

public static boolean isOverlapping(Date start1, Date end1, Date start2, Date end2) {
    return start1.before(end2) && start2.before(end1);
}

This code requires there to be at least one millisecond to be shared between the two periods to return true.

If abutting time periods are considered to "overlap" (eg 10:00-10:30 and 10:30-11:00) the logic needs to be tweaked ever so slightly:

public static boolean isOverlapping(Date start1, Date end1, Date start2, Date end2) {
    return !start1.after(end2) && !start2.after(end1);
}

This logic more often comes up in database queries, but the same approach applies in any context.

Once you realise just how simple it is, you at first kick yourself, then you put it in the bank!

Answer 2

tl;dr

( startA.isBefore( stopB ) ) && ( stopA.isAfter( startB ) ) 

LocalTime

If you really want to work with a generic time-of-day without the context of a date and time zone, use the LocalTime class.

LocalTime startA = LocalTime.of( 7 , 0 );
LocalTime stopA = LocalTime.of( 10 , 30 );

LocalTime startB = LocalTime.of( 10 , 0 );
LocalTime stop2B = LocalTime.of( 11 , 30 );

Validate the data, being sure the ending is after the beginning (or equal). A briefer way of saying that is “beginning is not after ending”.

Boolean validA = ( ! startA.isAfter( stopA ) ) ;
Boolean validB = ( ! startB.isAfter( stop2B ) ) ;

Per this Answer by Meno Hochschild, using the Half-Open approach to defining a span of time where the beginning is inclusive while the ending is exclusive, we can use this logic:

(StartA < EndB) and (EndA > StartB)

Boolean overlaps = ( 
    ( startA.isBefore( stopB ) ) 
    && 
    ( stopA.isAfter( startB ) ) 
) ;

Note that LocalTime is constrained to a single generic 24-hour day. The times cannot go past midnight, cannot wrap around into another. There are no other days to consider. Validate your inputs to verify the beginning time comes before the end, or they are equal (if that suits your business rules).

if( stopA.isBefore( startA ) ) { … handle error  } 

if( stopB.isBefore( startB ) ) { … handle error  } 

ZonedDateTime

If you want to test actual moments on the timeline, you must adjust these time-of-day objects into the context of dates and a time zone. Apply a ZoneId to get a ZonedDateTime object.

ZoneId z = ZoneId.of( "America/Montreal" );
LocalDate today = LocalDate.now( z );
ZonedDateTime zdt = ZonedDateTime.of( today , startA , z);

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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.

Answer 3

If interval is opened (for example, some process is not finished yet) and end date might be null:

public static boolean isOverlapping(Date start1, Date end1, Date start2, Date end2)
{
    return
            ((null == end2) || start1.before(end2)) &&
            ((null == end1) || start2.before(end1)) ;
}

Answer 4

JOda Time has this functionality baked in. It's very well-built and on JSR route to replace the broken Java Calendar API. You should probably considering using it.

Answer 5

EDIT:

Here is the working method:

public boolean isOverlapping(Date start1, Date end1, Date start2, Date end2) {
    return start1.compareTo(end2) <= 0 && end1.compareTo(start2) >= 0;
}

And here is proof for everyone to try it:

@Test
public void isOverlapping_base() {
    Assert.assertTrue(isOverlapping(getDate(2014, 1, 1),
            getDate(2014, 3, 31), getDate(2014, 1, 2),
            getDate(2014, 4, 1)));
    
    Assert.assertTrue(isOverlapping(getDate(2014, 1, 2),
            getDate(2014, 4, 1), getDate(2014, 1, 1),
            getDate(2014, 3, 31)));
    
    Assert.assertTrue(isOverlapping(getDate(2014, 1, 1),
            getDate(2014, 4, 1), getDate(2014, 1, 2),
            getDate(2014, 3, 31)));
    
    Assert.assertTrue(isOverlapping(getDate(2014, 1, 2),
            getDate(2014, 3, 31), getDate(2014, 1, 1),
            getDate(2014, 4, 1)));
    
    Assert.assertFalse(isOverlapping(getDate(2014, 1, 1),
            getDate(2014, 1, 31), getDate(2014, 3, 1),
            getDate(2014, 3, 31)));
    
    Assert.assertFalse(isOverlapping(getDate(2014, 3, 1),
            getDate(2014, 3, 31), getDate(2014, 1, 1),
            getDate(2014, 1, 31)));
}

Date getDate(int year, int month, int date) {
    Calendar working = Calendar.getInstance();
    working.set(year, month - 1, date, 0, 0, 0); 
    working.set(Calendar.MILLISECOND, 0);
    return working.getTime();
}