Convert Date Format Example in Java

Introduction

Convert Date Format is a classic Java console program that demonstrates the concept with complete source code and sample output. Conversion programs transform values between formats, units or representations.

This tutorial walks through the program line by line, explains how the logic works, and highlights best practices you can apply in your own code.

Convert Date Format Example Program

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

public class ConvertDateFormat{
    public static void main(String[] args) {
        try {
            String datee = "21/08/2012";
			System.out.println("The input date is:"+datee);
            DateFormat format1 = new SimpleDateFormat("dd/MM/yyyy");
            Date date = format1.parse(datee);
            DateFormat format2 = new SimpleDateFormat("MM-dd-yyyy");
            datee = format2.format(date);
            System.out.println("Converted date is : " + datee);
        }
        catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

Sample Output

The input date is:21/08/2012
Converted date is : 08-21-2012

When to use

Use unit conversion programs when reading sensor data, building calculators, or localizing measurements for users.

How it works

1. Execution begins in the main method — the JVM calls this method when you run the class.

2. import java.text.DateFormat; imports a class used later in the program.

3. import java.text.ParseException; imports a class used later in the program.

4. import java.text.SimpleDateFormat; imports a class used later in the program.

5. import java.util.Date; imports a class used later in the program.

6. String datee = "21/08/2012"; updates a variable used in the calculation or output.

7. A println / print call writes text to the console — part of the sample output below.

8. A println / print call writes text to the console — part of the sample output below.

Best Practices

• Use double (or BigDecimal for money) to avoid integer division rounding errors.
• Apply multiplication before addition — match the formula order exactly.
• Validate input with hasNextDouble() before reading, as shown in the Scanner examples.

Common Mistakes

• Using integer division (9/5 as 1) instead of floating-point (9.0/5.0).
• Applying the wrong formula order — (C + 32) * 9/5 is not the same as C * 9/5 + 32.
• Forgetting to close the Scanner when finished (call in.close() in longer programs).