Java .compareTo()

The Date.compareTo() method compares one Date object with another and returns an integer value accordingly.

Syntax

thisDate.compareTo(argumentDate)

The Date.compareTo() takes only one parameter:

• argumentDate: A Date object to be compared chronologically with the given date.

It returns:

• The value 0 if argumentDate is equal to thisDate.
• A value less than 0 if thisDate is before argumentDate.
• A value greater than 0 if thisDate is after argumentDate.

The function throws a single exception, a NullPointerException, if argumentDate is null.

Example

The following example shows the implementation of Date.compareTo():

import java.util.Date;

public class Main {
  public static void main(String[] args) {

    Date firstDate = new Date(2023, 1, 18);
    Date secondDate = new Date(2023, 1, 19);
    Date thirdDate = new Date(2023, 1, 18);
    Date fourthDate = new Date(2023, 1, 17);
    Date nullDate = null;

    System.out.println("Comparing firstDate and secondDate: " + firstDate.compareTo(secondDate));
    System.out.println("Comparing firstDate and thirdDate: " + firstDate.compareTo(thirdDate));
    System.out.println("Comparing firstDate and fourthDate: " + firstDate.compareTo(fourthDate));
    System.out.println("Comparing firstDate and nullDate: " + firstDate.compareTo(nullDate));
   }
}

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The output will be:

Comparing firstDate and secondDate: -1
Comparing firstDate and thirdDate: 0
Comparing firstDate and fourthDate: 1
Exception in thread "main" java.lang.NullPointerException
       at java.base/java.util.Date.getMillisOf(Date.java:956)
       at java.base/java.util.Date.compareTo(Date.java:979)
       at Main.main(Main.java:15)

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