Examples

1. Generating Log Messages

In logging systems, it’s common to format log messages to include timestamps, log levels, and specific message details. The Formatter class helps maintain a consistent format.

Formatter formatter = new Formatter();
String logMessage = formatter.format("%1$tF %1$tT - [%2$s] - %3$s", new java.util.Date(), "INFO", "Application started successfully").toString();
System.out.println(logMessage); // 2024-12-27 14:35:20 - [INFO] - Application started successfully

2. Creating a Table of Data (Report Generation)

Formatter is useful in generating tabular data, such as a report for employees, students, or any structured data where alignment is crucial

Formatter formatter = new Formatter();
formatter.format("| %-20s | %-10s | %-10s | %-15s |\n", "Employee", "Department", "Salary", "Joining Date");
formatter.format("| %-20s | %-10s | %-10.2f | %-15s |\n", "Alice", "HR", 75000.50, "2020-01-15");
formatter.format("| %-20s | %-10s | %-10.2f | %-15s |\n", "Bob", "Engineering", 95000.75, "2018-05-20");
formatter.format("| %-20s | %-10s | %-10.2f | %-15s |\n", "Charlie", "Marketing", 80000.00, "2019-11-30");

System.out.println(formatter.toString());

Output

| Employee             | Department | Salary    | Joining Date    |
| Alice                | HR         | 75000.50  | 2020-01-15      |
| Bob                  | Engineering| 95000.75  | 2018-05-20      |
| Charlie              | Marketing  | 80000.00  | 2019-11-30      |

3. Currency and Number Formatting

Formatter can be used to format financial data according to the required conventions, including currency formatting.

Locale locale = Locale.US;
Formatter formatter = new Formatter(locale);
formatter.format("Price: %.2f", 12345.6789);
System.out.println(formatter.toString());  // $12,345.68

locale = Locale.FRANCE;
formatter = new Formatter(locale);
formatter.format("Price: %.2f", 12345.6789);
System.out.println(formatter.toString());  // 12 345,68 €

4. Generating a Custom File Output (Exporting Data)

Formatter can be used to create formatted text files, for instance, when exporting data to CSV or any structured text file. In this case, Formatter is used to format and write data to a CSV file.

import java.io.File;
import java.io.IOException;
import java.util.Formatter;

public class CSVExport {
    public static void main(String[] args) throws IOException {
        Formatter formatter = new Formatter(new File("employee_data.csv"));
        formatter.format("Employee Name,Department,Salary,Joining Date\n");
        formatter.format("Alice,HR,75000.50,2020-01-15\n");
        formatter.format("Bob,Engineering,95000.75,2018-05-20\n");
        formatter.format("Charlie,Marketing,80000.00,2019-11-30\n");
        formatter.close();
        System.out.println("File exported successfully!");
    }
}

Output (file employee_data.csv):

Employee Name,Department,Salary,Joining Date
Alice,HR,75000.50,2020-01-15
Bob,Engineering,95000.75,2018-05-20
Charlie,Marketing,80000.00,2019-11-30

5. Locale-specific Date Formatting

Formatter is useful in generating date/time strings in different formats based on the locale. Here, Formatter is used to format dates based on the locale.

import java.util.Formatter;
import java.util.Locale;

public class DateFormatting {
    public static void main(String[] args) {
        Formatter formatter = new Formatter();
        formatter.format("Today's date in US: %1$tm/%1$td/%1$tY", new java.util.Date());
        System.out.println(formatter.toString());  // Today's date in US: 12/27/2024
        
        Locale frenchLocale = Locale.FRANCE;
        formatter = new Formatter(frenchLocale);
        formatter.format("Today's date in France: %1$td/%1$tm/%1$tY", new java.util.Date());
        System.out.println(formatter.toString());  // Today's date in France: 27/12/2024
    }
}

6. File Content Formatting for Reporting

In a reporting system, if we need to format large amounts of data to generate readable reports, Formatter can be used. In this example, Formatter is used to generate a formatted sales report with headers and data.

import java.util.Formatter;

public class ReportFormatter {
    public static void main(String[] args) {
        Formatter formatter = new Formatter();
        String title = "Monthly Sales Report";
        String header = "| %-15s | %-10s | %-15s | %-15s |\n";
        String data = "| %-15s | %-10d | %-15.2f | %-15s |\n";
        
        // Header
        formatter.format(header, "Product", "Quantity", "Unit Price", "Total Sales");
        
        // Data
        formatter.format(data, "Product A", 100, 15.75, "$1,575.00");
        formatter.format(data, "Product B", 200, 25.00, "$5,000.00");
        
        System.out.println(title);
        System.out.println(formatter.toString());
    }
}

Monthly Sales Report
| Product         | Quantity  | Unit Price       | Total Sales      |
| Product A       | 100       | 15.75            | $1,575.00        |
| Product B       | 200       | 25.00            | $5,000.00        |

7. Formating Time and Duration

Formatter can be used to format elapsed time or duration for display purposes, e.g., when displaying download or processing times. In this case, Formatter is used to format the duration in a standard hh:mm:ss format.

import java.util.Formatter;

public class DurationFormatter {
    public static void main(String[] args) {
        long seconds = 3661; // 1 hour, 1 minute, and 1 second
        Formatter formatter = new Formatter();
        formatter.format("Elapsed Time: %02d:%02d:%02d", 
                         (seconds / 3600), // hours
                         (seconds % 3600) / 60, // minutes
                         seconds % 60); // seconds
        System.out.println(formatter.toString()); //Elapsed Time: 01:01:01
    }
}