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Java Dateencapsulates the current time and date. The Date class does this with the help of two constructors - Date()and Date(long millisec)constructor.

We use Date()the constructor to initialize the object with the current time and date. On the other hand, Date(long millisec)the constructor takes the number of milliseconds since midnight on January 1, 1970 as a parameter.

But the output we get is not yyyy-MM-ddin format. This article will show how we can generate output in this format.

We use the get method in Java date()to get the current date and time. For this, we use toString()the Date object with the get method. Look at the following example to understand it.

import java.util.Date;
public class DateExample {
  public static void main(String args[]) {
    // Create a date object
    Date date_of_today = new Date();

    // Use toString() to print the date
    System.out.println(date_of_today.toString());
  }
}

Output:

Mon Jan 10 09:58:43 UTC 2022

This example uses date_of_todaythe DDate object to instantiate and toString()the date method to print the date. Notice that we get output that contains the day, month, day and year, and 小时:分钟:秒the time in a formatted format.

This poses a problem when we use two or more dates. To remove the names of the dates and times from this output, we can use printf()the method in two ways. The first uses the symbols %and $.

See the example below.

import java.util.Date;
public class DateExample {
  public static void main(String args[]) {
    // Create a new object
    Date date_of_today = new Date();

    // Display the date
    System.out.printf("%1$s %2$tB %2$td, %2$tY", "Date:", date_of_today);
  }
}

Output:

Date: January 10, 2022

The second method is to use <flag. Let's look at the same example again.

import java.util.Date;
public class DateExample {
  public static void main(String args[]) {
    // Create a new object
    Date date_of_today = new Date();

    // display the date
    System.out.printf("%s %tB %<te, %<tY", "Date:", date_of_today);
  }
}

Output:

Date: January 10, 2022

Note that in these examples, the time is omitted. But we still don't get yyyy-MM-ddoutput in the format of . Let's see how to deal with this.

Convert date to YYYY-MM-DDFormat in Java

Java has a java.timepackage. java.timeInstead of using the Date class to work with date and time, we can use the package. Let's look at an example.

// import the java.time package
import java.time.LocalDate;

public class DemoOfDate {
  public static void main(String[] args) {
    // create an object for date
    LocalDate date_of_today = LocalDate.now();

    // Display the date
    System.out.println(date_of_today);
  }
}

Output:

2022-01-10

In this example, we use java.timethe package and LocalDatethe class. This time we get yyyy-MM-ddthe output in the format. java.timeThe package has four main classes.

• LocalDate- It yyyy-MM-ddgives date as output in year, month, day or format.
• LocalTime- It HH-mm-ss-nsgives the output in the form of time and nanoseconds.
• LocalDateTime- It yyyy-MM-dd-HH-mm-ss-nsgives output in terms of date and time.
• DateTimeFormatter- This acts as a formatter for date-time objects, both for displaying and parsing them.

Notice that we have used the class in the above example LocalDate. Also, we have used now()the method. The method in java now()is LocalTimea method of the class. It gets the current time in the default time zone from the system clock.

grammar:

public static LocalTime now()

We are not now()passing any parameters in the method. Another way is yyyy-MM-ddto get the output in format.

YYYY-MM-DDFormatting a date in Java

To change the calendar date to yyyy-MM-dda format, we can also use the concept of formatting. It makes working with date and time more flexible.

For this, we use the method java.timefrom the package ofPattern(). The various ways in which we can use ofPattern()the method to get the output are as follows.

• yyyy-MM-dd - This gives the output as 2022-01-25
• dd/MM/yyyy- This gives the output as25/01/2022
• dd-MMM-yyyy- This gives the output as25/01/2022
• E, MMM dd yyyy- This gives the output asTue, Jan 25 2022

Let’s look at an example.

// import the LocalDateTime class
import java.time.LocalDateTime;
// import the DateTimeFormatter class
import java.time.format.DateTimeFormatter;

public class DemoOfDate {
  public static void main(String[] args) {
    LocalDateTime date_of_today = LocalDateTime.now();

    System.out.println("Output before formatting: " + date_of_today);
    DateTimeFormatter format_date_of_today = DateTimeFormatter.ofPattern("yyyy-MM-dd");

    String formattedDate = date_of_today.format(format_date_of_today);
    System.out.println("Output after formatting: " + formattedDate);
  }
}

Output:

Output before formatting: 2022-01-01T10:46:21.449669400
Output after formatting: 2022-01-01

Note that we can use formatting to get yyyy-MM-ddoutput in . We can also move values ​​in all of these formats.

For example, when we ofPattern()pass a string in method yyyy-MM-dd, we can change that string to yyyy-dd-MMor dd-MM-yyyyor in any other way as required. This applies to ofPattern()all the formats provided by method.

We have used another approach here - format()the method. format()The method formats a string using the given locale, parameters and Java format.

If we do not specify a locale, format()the method calls Locale.getDefault()the method to get the default locale. format()The method works printf()the same way as the function.

SimpleDateFormatUsing Classes in Java

To get yyyy-MM-ddthe output in format, we can use SimpleDateFormatclass. It provides methods to format (change date to string) and parse (change string to date) date and time in Java.

By inheriting from it, it can java.text.DateFormatbe used with the class. Let's see an example.

import java.text.SimpleDateFormat;
import java.util.Date;
public class SimpleDateFormatDemo {
  public static void main(String[] args) {
    Date date_of_today = new Date();
    SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
    String stringDate = format.format(date_of_today);
    System.out.println(stringDate);
  }
}

Output:

2022-01-01

in conclusion

This article discusses how to change calendar date into yyyy-MM-ddformat in Java. It includes using java.timethe package, using toPattern()the method and SimpleDateFormatthe class for formatting. The various methods are toString()the and now()methods.

We can get yyyy-MM-ddthe output in format and use it when it contains multiple dates.