Format Specifiers in Java

Format specifiers begin with a percent character (%) and terminate with a “type character, ” which indicates the type of data (int, float, etc.) that will be converted the basic manner in which the data will be represented (decimal, hexadecimal, etc.)
The general syntax of a format specifier is

% [flags] [width] [.precision] [argsize] typechar

The format() method of Formatter class accepts a wide variety of format specifiers. When an uppercase specifier is used, then letters are shown in uppercase. Otherwise, the upper- and lowercase specifiers perform the same conversion.

Format Specifier	Conversion Applied
%%	Inserts a % sign
%x %X	Integer hexadecimal
%t %T	Time and Date
%s %S	String
%n	Inserts a newline character
%o	Octal integer
%f	Decimal floating-point
%e %E	Scientific notation
%g	Causes Formatter to use either %f or %e, whichever is shorter
%h %H	Hash code of the argument
%d	Decimal integer
%c	Character
%b %B	Boolean
%a %A	Floating-point hexadecimal

1. Space format specifier : When creating columns of numbers, it is sometimes very useful to print a space before a positive number so that positive and negative number get aligned. To do this, space format specifier can be used.

   Syntax:

   Formatter().format("% d", -111);
   Formatter().format("% d", 111);
   
   Output:
   -111
    111
   

   Example:

   // Java program to demonstrate
   // the space format specifier
   
   import java.util.*;
   
   class GFG {
       public static void main(String args[])
       {
   
           // create Formatter class object
           Formatter formatter = new Formatter();
   
           // Use Space format specifier
           formatter.format("%d", -111);
           System.out.println(formatter);
   
           formatter = new Formatter();
           formatter.format("% d", 111);
           System.out.println(formatter);
   
           formatter = new Formatter();
           formatter.format("% d", -222);
           System.out.println(formatter);
   
           formatter = new Formatter();
           formatter.format("% d", 222);
           System.out.println(formatter);
       }
   }
   Output:

   -111
    111
   -222
    222
   

2. + Sign Specifier: This adds the + sign before positive numeric value, and has no effect on negative numeric value.

   Syntax:

   Formatter().format("%+d", 111);
   
   Output:
   +111
   

   Example:

   // Java program to demonstrate
   // the + sign Specifier format specifiers.
   
   import java.util.*;
   
   class GFG {
       public static void main(String args[])
       {
   
           // create Formatter class object
           Formatter formatter = new Formatter();
   
           // + sign specifier
           formatter = new Formatter();
           formatter.format("%+d", 111);
           System.out.println(formatter);
   
           // + sign specifier
           // on - sign, it will have no effect
           formatter = new Formatter();
           formatter.format("%+d", -111);
           System.out.println(formatter);
       }
   }
   Output:

   +111
   -111
   

3. ( specifier: This specifier puts the negative numeric values inside the parentheses, and has no effect on the positive numeric values.

   Syntax:

   Formatter().format("%(d", -111);
   Formatter().format("%(d", 111);
   
   Output:
   (111)
   111
   

   Example:

   // Java program to demonstrate
   // the ( Specifiers format specifiers.
   
   import java.util.*;
   
   class GFG {
       public static void main(String args[])
       {
   
           // create Formatter class object
           Formatter formatter = new Formatter();
   
           // ( Specifier
           formatter = new Formatter();
           formatter.format("%(d", -111);
           System.out.println(formatter);
   
           formatter = new Formatter();
           formatter.format("%(d", 111);
           System.out.println(formatter);
       }
   }
   Output:

   (111)
   111
   

4. Comma, Specifier: For displaying large numbers, it is often useful to add grouping separators by comma (, ). For example, the value is 1000000 more easily read when formatted as 1, 000, 000. To add grouping specifiers (, ) use the comma(, ) Specifier.

   Syntax:

   Formatter().format("%, d", 1000000);
   
   Output:
   1, 000, 000

   Example:

   // Java program to demonstrate
   // the comma format specifiers.
   
   import java.util.*;
   
   public class GFG {
       public static void main(String args[])
       {
   
           // create Formatter class object
           Formatter formatter = new Formatter();
   
           // comma Specifier
           formatter = new Formatter();
           formatter.format("%, d", 1000000);
           System.out.println(formatter);
   
           // comma Specifier
           formatter = new Formatter();
           formatter.format("%, .3f", 32659526566.4521);
           System.out.println(formatter);
       }
   }
   Output:

   1, 000, 000
   32, 659, 526, 566.452
   

5. Left Justification(-) Specifier: By default all output is right-shifted. That is, if the field width is longer than the data printed, data will be placed on the right side of the field. One can force output to be left-justified by placing a minus sign directly after the %. For instance, %-20.4f left justifies a floating-point number with two decimal places in a 20-character field.

   Syntax:

   Formatter().format("|%-20.4f|", 1234.1234);
   
   Output:
   |           1234.1234|
   |1234.1234           |
   

   Example:

   // Java program to demonstrate
   // the left justification format specifiers.
   
   import java.util.*;
   
   class GFG {
       public static void main(String args[])
       {
   
           // create Formatter class object
           Formatter formatter = new Formatter();
   
           // right justify by default
           formatter = new Formatter();
           formatter.format("|%20.4f|", 1234.1234);
           System.out.println(formatter);
   
           // left justify
           formatter = new Formatter();
           formatter.format("|%-20.4f|", 1234.1234);
           System.out.println(formatter);
       }
   }
   Output:

   |           1234.1234|
   |1234.1234           |
   

6. The %n format specifiers:
   The %n format specifier is different from the others in that it doesn’t take arguments. It is simply an escape sequence that inserts a character into the output. The %n inserts a newline. It can’t be entered directly into the format string.

   // Java program to demonstrate
   // the newline %n format specifiers.
   
   import java.util.*;
   
   public class GFG {
       public static void main(String args[])
       {
           // create Formatter class object
           Formatter formatter = new Formatter();
   
           // newline format specifier
           formatter.format("Geeks %nFor %nGeeks");
   
           // Print the output
           System.out.println(formatter);
       }
   }
   Output:

   Geeks 
   For 
   Geeks
   

7. The %% format specifiers:
   The %% format specifier is different from the others in that it doesn’t take arguments. It is simply an escape sequence that inserts a character into the output. The %% inserts a % sign. It can’t be entered directly into the format string.

   // Java program to demonstrate
   // the %% format specifiers.
   
   import java.util.*;
   
   public class GFG {
       public static void main(String args[])
       {
           // create Formatter class object
           Formatter formatter = new Formatter();
   
           // %% format specifier
           formatter.format("10 %% 4 = 2");
   
           // Print the output
           System.out.println(formatter);
       }
   }
   Output:

   10 % 4 = 2
   

8. The %x %X format specifiers:
   The %x or %X format specifier is is used to represent the integer Hexadecimal value. %x displays the hexadecimal values with lowercase alphabets whereas the %X specifier displays the hexadecimal values with uppercase alphabets.

   // Java program to demonstrate
   // the integer-Hexadecimal %x and %X
   // format specifiers.
   
   import java.util.*;
   
   public class GFG {
       public static void main(String args[])
       {
           // create Formatter class object
           Formatter formatter = new Formatter();
   
           // %x format specifier
           // It prints the number in Hexadecimal
           // with lowercase alphabets
           formatter.format("%x", 250);
   
           // Print the output
           System.out.println("LowerCase Hexadecimal"
                              + " using %x: "
                              + formatter);
   
           // %X format specifier
           // It prints the number in Hexadecimal
           // with uppercase alphabets
           formatter = new Formatter();
           formatter.format("%X", 250);
   
           // Print the output
           System.out.println("UpperCase Hexadecimal"
                              + " using %X: "
                              + formatter);
       }
   }
   Output:

   LowerCase Hexadecimal using %x: fa
   UpperCase Hexadecimal using %X: FA
   

9. The %e %E format specifiers:
   The %e or %E format specifier is is used to represent the Scientific Notation of a value. %e displays the Scientific Notation with lowercase alphabets whereas the %E specifier displays the Scientific Notation with uppercase alphabets.

   // Java program to demonstrate
   // the Scientific Notation %e and %E
   // format specifiers.
   
   import java.util.*;
   
   public class GFG {
       public static void main(String args[])
       {
           // create Formatter class object
           Formatter formatter = new Formatter();
   
           // %e format specifier
           // It prints the number in Scientific Notation
           // with lowercase alphabets
           formatter.format("%e", 123.1234);
   
           // Print the output
           System.out.println("LowerCase Scientific Notation"
                              + " using %e: "
                              + formatter);
   
           // %E format specifier
           // It prints the number in Scientific Notation
           // with uppercase alphabets
           formatter = new Formatter();
           formatter.format("%E", 123.1234);
   
           // Print the output
           System.out.println("UpperCase Scientific Notation"
                              + " using %E: "
                              + formatter);
       }
   }
   Output:

   LowerCase Scientific Notation using %e: 1.231234e+02
   UpperCase Scientific Notation using %E: 1.231234E+02
   

10. Precision Formats
    A precision specifier can be applied to the %f, %e, %g, and %s format specifiers.

    // Java program to demonstrate
    // Prrecision Format specifiers
    
    import java.util.Formatter;
    
    public class GFG {
        public static void main(String args[])
        {
    
            // Create the Formatter instance
            Formatter formatter = new Formatter();
    
            // added floating-point data
            // using the %f or %e specifiers,
            // Format to 2 decimal places
            // in a 16 character field.
            formatter = new Formatter();
            formatter.format("%16.2e", 123.1234567);
            System.out.println("Scientific notation to 2 places: "
                               + formatter);
    
            // Format 4 decimal places.
            formatter = new Formatter();
            formatter.format("%.4f", 123.1234567);
            System.out.println("Decimal floating-point"
                               + " notation to 4 places: "
                               + formatter);
    
            // Format 4 places.
            // The %g format specifier causes Formatter
            // to use either %f or %e, whichever is shorter
            formatter = new Formatter();
            formatter.format("%.4g", 123.1234567);
            System.out.println("Scientific or Decimal floating-point "
                               + "notation to 4 places: "
                               + formatter);
    
            // Display at most 15 characters in a string.
            formatter = new Formatter();
            formatter.format("%.15s", "12345678901234567890");
            System.out.println("String notation to 15 places: "
                               + formatter);
    
            // Format into 10 digit
            formatter = new Formatter();
            formatter.format("%010d", 88);
            System.out.println("value in 10 digits: "
                               + formatter);
        }
    }
    Output:

    Scientific notation to 2 places:         1.23e+02
    Decimal floating-point notation to 4 places: 123.1235
    Scientific or Decimal floating-point notation to 4 places: 123.1
    String notation to 15 places: 123456789012345
    value in 10 digits: 0000000088