How to Change the Date Format in a Java String

To change the date format in a Java string, you can use the SimpleDateFormat class, which is part of the java.text package. This class allows you to specify a pattern for parsing and formatting dates.

Here are two possible approaches to changing the date format in a Java string:

Approach 1: Using SimpleDateFormat

1. Create an instance of the SimpleDateFormat class, passing the desired date format pattern as a string to the constructor. The pattern should contain a combination of letters and symbols that represent the different elements of the date.

Example:

SimpleDateFormat inputFormat = new SimpleDateFormat("yyyy-MM-dd");

2. Use the parse() method of the SimpleDateFormat class to parse the input string into a Date object. This method throws a ParseException if the input string does not match the specified format.

Example:

String inputString = "2021-07-01";
Date date = inputFormat.parse(inputString);

3. Create another instance of the SimpleDateFormat class with the desired output format pattern.

Example:

SimpleDateFormat outputFormat = new SimpleDateFormat("dd/MM/yyyy");

4. Use the format() method of the SimpleDateFormat class to format the Date object into a string with the desired output format.

Example:

String outputString = outputFormat.format(date);

Here’s the complete code snippet:

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

public class DateFormatter {
    public static void main(String[] args) throws ParseException {
        SimpleDateFormat inputFormat = new SimpleDateFormat("yyyy-MM-dd");
        String inputString = "2021-07-01";
        Date date = inputFormat.parse(inputString);
        SimpleDateFormat outputFormat = new SimpleDateFormat("dd/MM/yyyy");
        String outputString = outputFormat.format(date);
        System.out.println(outputString);
    }
}

This will output: “01/07/2021”.

Approach 2: Using DateTimeFormatter (Java 8 and later)

Starting from Java 8, a new date and time API was introduced in the java.time package. This API provides the DateTimeFormatter class, which can be used to change the date format in a Java string.

1. Create an instance of the DateTimeFormatter class using the ofPattern() method, passing the desired date format pattern as a string.

Example:

DateTimeFormatter inputFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");

2. Use the parse() method of the DateTimeFormatter class to parse the input string into a LocalDate object. This method throws a DateTimeParseException if the input string does not match the specified format.

Example:

String inputString = "2021-07-01";
LocalDate date = LocalDate.parse(inputString, inputFormatter);

3. Create another instance of the DateTimeFormatter class with the desired output format pattern.

Example:

DateTimeFormatter outputFormatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");

4. Use the format() method of the DateTimeFormatter class to format the LocalDate object into a string with the desired output format.

Example:

String outputString = date.format(outputFormatter);

Here’s the complete code snippet:

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

public class DateFormatter {
    public static void main(String[] args) {
        DateTimeFormatter inputFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        String inputString = "2021-07-01";
        LocalDate date = LocalDate.parse(inputString, inputFormatter);
        DateTimeFormatter outputFormatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
        String outputString = date.format(outputFormatter);
        System.out.println(outputString);
    }
}

This will output: “01/07/2021”.

These are two possible approaches to change the date format in a Java string. Both approaches are valid and can be used depending on the version of Java you are working with and your specific requirements.