How to Efficiently Calculate the Date Difference in Android/Java?

Determining Date Difference in Android/Java

Calculating the difference between two dates is a common requirement in various applications. In Android programming, there are multiple approaches to determine the number of days between the current date and a given date in the format "yyyy/mm/dd."

Using the JodaTime Library

For a reliable and flexible solution, consider utilizing the JodaTime library. It provides robust date handling and manipulation capabilities. Here's an example:

import org.joda.time.LocalDate;
import org.joda.time.Period;
import org.joda.time.PeriodType;

LocalDate today = LocalDate.now();
LocalDate thatDay = LocalDate.parse("1985/08/25");

Period period = new Period(thatDay, today, PeriodType.days());
long days = period.getDays();

This approach uses JodaTime to parse the given date string and calculate the difference in days from today.

Manual Approximation

Alternatively, you can attempt a manual approximation using the following steps:

• Parse the given date string into individual integer values for year, month, and day.
• Create two Calendar instances, one for the current date and one for the given date, and set their respective fields.
• Calculate the time difference in milliseconds between the two Calendar instances.
• Divide the time difference by the number of milliseconds in a day (24 60 60 * 1000) to obtain the approximate number of days.

Example Code:

SimpleDateFormat formatter = new SimpleDateFormat("yyyy/MM/dd");
Date d = formatter.parse("1985/08/25");

Calendar thatDay = Calendar.getInstance();
thatDay.setTime(d);
Calendar today = Calendar.getInstance();

long diff = today.getTimeInMillis() - thatDay.getTimeInMillis();
long days = diff / (24 * 60 * 60 * 1000);

Note: This manual approximation may not be entirely accurate for dates close to year or month boundaries.

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