## Monday, 4 January 2021

### Design Patterns

A software design pattern is a general, reusable solution to a commonly occurring problem within a given context in software design. It is not a finished design that can be transformed directly into the source or machine code.

There are mainly three categories of design patterns:

Creational Design Pattern

Structural Design Pattern
2. Bridge Pattern
3. Composite Pattern

Behavioral Design Pattern
2. Command Pattern
3. Interpreter Pattern

## Sunday, 23 February 2020

### Java 8 | Calculate days between two dates

We have already seen to calculate the number of Days between two dates prior to Java 8.

Today, we will discuss how to calculate the number of days between two dates in Java 8.

To calculate the days between two dates we can use the DAYS.between() method of java.time.temporal.ChronoUnit.

Syntax of DAYS.between():

long noOfDaysBetween = DAYS.between(startDate, endDate);

// or alternatively
long noOfDaysBetween = startDate.until(endDate, DAYS);

The startDate is Inclusive and endDate is Exclusive in the calculation of noOfDaysBetween

1. Number of Days between two Dates using DAYS.between() method

package com.algorithmforum.date;

import java.time.LocalDate;
import java.time.Month;
import java.time.temporal.ChronoUnit;

public class DaysDiffJava8 {
public static void main(String[] args) {
// 24-May-2017, change this to your desired Start Date
LocalDate dateBefore = LocalDate.of(2017, Month.MAY, 24);

// 29-July-2017, change this to your desired End Date
LocalDate dateAfter = LocalDate.of(2017, Month.JULY, 29);

// Logic to calculate the days difference.
long noOfDaysBetween = ChronoUnit.DAYS.between(dateBefore, dateAfter);
System.out.println(noOfDaysBetween);
}
}

2. Parsing the Dates and then calculating the days between them
In the above example we are passing the date in desired format, however if you have the date as a String then you can parse the date to convert it into a Java 8 LocalDate. After the parsing, we are calculating the days between similar to the above example.

You can parse a date of any format to the desired format. Refer Java – parse date tutorial for date parsing examples.

package com.algorithmforum.date;

import java.time.LocalDate;
import java.time.temporal.ChronoUnit;

public class DaysDiffJava8 {
public static void main(String[] args) {
String dateBeforeString = "2017-05-24";
String dateAfterString = "2017-07-29";

// Parsing the date
LocalDate dateBefore = LocalDate.parse(dateBeforeString);
LocalDate dateAfter = LocalDate.parse(dateAfterString);

// calculating number of days in between
long noOfDaysBetween = ChronoUnit.DAYS.between(dateBefore, dateAfter);

// displaying the number of days
System.out.println(noOfDaysBetween);
}
}

### Java | Calculate number of days between two dates

In this tutorial, we will see how to calculate the number of days between two dates. This solution for the Java 7 version or below.

Program to find the number of Days between two Dates.

Steps:
1. Take dates input as Strings.
2. Parse the input string dates 'Date'.
3. Finds the difference between them in milliseconds.
4. Convert the milliseconds into Days.
5. Displays the result as output.

package com.algorithmforum.date;

import java.util.Date;
import java.text.SimpleDateFormat;

class DateDifference {
public static void main(String args[]) {
SimpleDateFormat myFormat = new SimpleDateFormat("dd MM yyyy");
String dateBeforeString = "31 01 2014";
String dateAfterString = "02 02 2014";

try {
Date dateBefore = myFormat.parse(dateBeforeString);
Date dateAfter = myFormat.parse(dateAfterString);
long difference = dateAfter.getTime() - dateBefore.getTime();
float daysBetween = (difference / (1000 * 60 * 60 * 24));
/*
* You can also convert the milliseconds to days using this method
* float daysBetween = TimeUnit.DAYS.convert(difference, TimeUnit.MILLISECONDS)
*/
System.out.println("Number of Days between dates: " + daysBetween);
} catch (Exception e) {
e.printStackTrace();
}
}
}