ChronoLocalDateTime until() method in Java with Examples

until() method of the ChronoLocalDateTime interface used to calculate the amount of time between two ChronoLocalDateTime objects using TemporalUnit. The start and end points are this and the specified ChronoLocalDateTime passed as a parameter. The result will be negative if the end is before the start. The calculation returns a whole number, representing the number of complete units between the two ChronoLocalDateTime. This instance is immutable and unaffected by this method call.
Syntax:

public long until(Temporal endExclusive, 
                  TemporalUnit unit)

Parameters: This method accepts two parameters: 

• endExclusive which is the end date, exclusive, which is converted to a ChronoLocalDateTime and
• unit which is the unit to measure the amount.

Return value: This method returns the amount of time between this ChronoLocalDateTime and the end ChronoLocalDateTime.
Exception:This method throws following Exceptions: 

• DateTimeException – if the amount cannot be calculated, or the ending temporal cannot be converted to a ChronoLocalDateTime.
• UnsupportedTemporalTypeException – if the unit is not supported.
• ArithmeticException – if numeric overflow occurs.

Below programs illustrate the until() method: 
Program 1:

Java

// Java program to demonstrate
// ChronoLocalDateTime.until() method

import java.time.*;
import java.time.chrono.*;
import java.time.temporal.*;

public class GFG {
    public static void main(String[] args)
    {
        // create ChronoLocalDateTime objects
        ChronoLocalDateTime z1
            = LocalDateTime
                  .parse("2019-12-31T19:15:30");

        ChronoLocalDateTime z2
            = LocalDateTime.parse(
                "2018-10-25T23:12:31.123");

        // apply until method of ChronoLocalDateTime class
        long result
            = z1.until(z2,
                       ChronoUnit.HOURS);

        // print results
        System.out.println("Result in HOURS: "
                           + result);
    }
}

Output:

Result in HOURS: -10364

Program 2:

Java

// Java program to demonstrate
// ChronoLocalDateTime.until() method

import java.time.*;
import java.time.chrono.*;
import java.time.temporal.*;

public class GFG {
    public static void main(String[] args)
    {
        // create ChronoLocalDateTime objects
        ChronoLocalDateTime z1
            = LocalDateTime
                  .parse("1999-10-31T19:15:30");

        ChronoLocalDateTime z2
            = LocalDateTime.parse(
                "1990-10-25T23:12:31.123");

        // applyendDateTime.parseChronoLocalDateTime class
        long result
            = z2.until(z1,
                       ChronoUnit.DAYS);

        // print results
        System.out.println("Result in DAYS: "
                           + result);
    }
}

Output:

Result in DAYS: 3292

References:
https://docs.oracle.com/javase/9/docs/api/java/time/temporal/Temporal.html#until-java.time.temporal.Temporal-java.time.temporal.TemporalUnit-