The Java printf() output method is used to generate a formatted string. Data from the arguments is written and formatted placeholders. In this tutorial we will explore the functionality of the printf() method.

The Java language was heavily inspired by the C programming language. As such, the printf() method is very similar in functionality to C’s printf method. The syntax and functionality is similar, but not identical to it’s C based inspiration.

printf() Method Signatures

The Java printf() method has three signatures.

• System.out.printf(string); – Applies no formatting, works like the println() method.
• System.out.printf(format, arguments); – Accepts a format string, arguments (one or more values)
• System.out.printf(locale, format, arguments); – Locale is the first parameter, to allow localization of the output.

The Java printf() method is a convenience method for the Java class java.util.Formatter.

Frequently, the Formatter class is used with a StringBuilder as follows:

StringBuilder sb = new StringBuilder();
Formatter formatter = new Formatter(sb);
formatter.format("Spring Framework %s", "Guru");
System.out.println(formatter);

Spring Framework Guru

Using printf()we can see the same functionality.

System.out.printf("Spring Framework %s", "Guru");

Spring Framework Guru

In the above examples, we are using the Format Specifier %s (String) which gets substituted with the first argument (“Guru”).

The Format Specifiers accept arguments positionally by default.

If we run the following:

System.out.printf("Spring Framework %s ", "Guru");
System.out.printf("%s %s %s", "Spring", "Framework", "Guru");

The output is:

Spring Framework Guru Spring Framework Guru

In this case, we can see the output of the two statements is on the same line. This is because unlike println(), the printf() does not append a new line character to the end of the output.

We can resolve this by adding new line escape character (\n) to the first statement.

System.out.printf("Spring Framework %s \n", "Guru");
System.out.printf("%s %s %s", "Spring", "Framework", "Guru");

We can see that this produces the output on two lines now.

Spring Framework Guru 
Spring Framework Guru

We can achieve the same effect using the Format Specifier %n too.

While the default behavior is to accept the arguments in the order they were passed, we can also reference them by position. Using x$ in the Format Specifier allows us to specify the position of the desired argument.

For example we can reverse the position of the words as follows:

System.out.printf("Spring Framework %s %n", "Guru");
System.out.printf("%s %s %s %n", "Spring", "Framework", "Guru");
System.out.printf("%3$s %2$s %1$s", "Spring", "Framework", "Guru");

This produces:

Spring Framework Guru 
Spring Framework Guru 
Guru Framework Spring

The Format Specifies follow the following syntax:

%[argument_index$][flags][width][.precision]specifier

The above syntax becomes more relevant as we use more complex types such as Dates.

• [argument_index$] – Position of the argument
• [flags] – used to modify the output. Common for formatting integers and floating point numbers
• [width]– Field width for outputting the argument. It represents the minimum number of charters written to the output
• [.precision]

Java Format Specifiers

These are the available Format Specifiers in Java.

• %a or %A Floating point hexadecimal
• %c Unicode character
• %b or %B Boolean
• %d decimal (integer) number (base 10)
• %e or %E exponential floating-point number
• %f floating-point number
• %h or %H Hash code of argument
• %i integer (base 10)
• %n line separator
• %o octal number (base 8)
• %s String
• %S String to Uppercase
• %u unsigned decimal (integer) number
• %x or %X number in hexadecimal (base 16)
• %t or %T formats date/time
• %% print a percent sign
• \% print a percent sign

Java Format Flags

Java Escape Characters

The following escape characters are available with printf()

• \b backspace
• \\ backslash
• \f next line first character starts to the right of current line last character
• \n newline
• \r carriage return
• \u Unicode
• \t tab

String Formatting

We’ve previously looked at several String formatting options earlier in this post. We do have several other options we can use with String values.

• %S – String to uppercase
• Left Justification Flag
• Output width

We can demonstrate these with the following:

System.out.printf("%s %S %S %n", "Spring", "Framework", "Guru");
System.out.printf("%10s %s %s %n", "Spring", "Framework", "Guru");
System.out.printf("%-10s %s %s %n", "Spring", "Framework", "Guru");

This will produce the following output:

Spring FRAMEWORK GURU 
    Spring Framework Guru 
Spring     Framework Guru 

You can see in the first line %S changed the last two words to uppercase.

Using %10s changed the size of the output to 10 characters, padding on the left.

Using %-10s changed the size of the output to 10 characters, String is left justified.

Boolean Formatting

The Boolean format specifier will return false if the value evaluates to false or is null. If the argument has a value, and is not a boolean false, it will return true.

The following statements demonstrate the boolean functionality.

System.out.printf("%b%n", null);
System.out.printf("%B%n", null);
System.out.printf("%B%n", true);
System.out.printf("%B%n", Boolean.FALSE);
System.out.printf("%b%n", 2024);
System.out.printf("%b%n", "Java Rocks!");
System.out.printf("%B%n", "JAVA ROCKS!");
System.out.printf("%b%n", LocalDateTime.now());

Produces the following output:

false
FALSE
TRUE
FALSE
true
true
TRUE
true

Character Formatting

Using %c will output a unicode character.

We can demonstrate the character formatting functionality with the examples below.

System.out.printf("%c%n", 'g');
System.out.printf("%C%n", 'g');
System.out.printf("%C%c%c%c%n", 71, 117, 114, 117);
System.out.printf("%c%c%c%c%n", '\u0047', '\u0075', '\u0072', '\u0075');

This will produce the following output:

g
G
Guru
Guru

You can see in the output we can use a character literal, unicode decimal, or escaped unicode value.

Integer Formatting

We can use the %d Format Specifier to work with integer values.

In the below example, we can see a demonstration of Integer formatting.

System.out.printf("My Integer: %d%n", 20000L);
System.out.printf(Locale.US, "%,d %n", 20000);
System.out.printf(Locale.GERMAN, "%,d %n", 20000);
System.out.printf(Locale.FRENCH, "%,d %n", 20000);

These statements will produce the following output:

My Integer: 20000
20,000 
20.000 
20 000 

Note how by passing the Locale, the separator changes to the country specific value.

Float and Double Formatting

For float and double values, we can use the %f Format Specifier. In the examples below, we pass different width and precision values to change the output. We can also use the %e Format Specifier to format the float value to scientific notation.

We can demonstration the formatting of floats and doubles with the following statements.

System.out.printf("%f%n", Math.PI);
System.out.printf("%20.2f%n", Math.PI);
System.out.printf("%20.18f%n", Math.PI);
System.out.printf("%5.2e%n", Math.PI);

These statements will produce the following output.

3.141593
                3.14
3.141592653589793000
3.14e+00

Time Formatting

For time values, we can use the %t or %T Format Specifier. These work in conjunction with conversion characters to extract and format portions of the time value.

We have a lot of versatility for formatting time values. The code below demonstrates some of the time formatting capabilities.

Date date = new Date();
System.out.println("Use t or T, same result");
System.out.printf("%tT%n", date);
System.out.printf("%TT%n%n", date);
System.out.println("Show time in 12 hour format");
System.out.printf("%tr%n%n", date);
System.out.println("Build Date by position");
System.out.printf("time is %tH:%tM:%tS%n%n", date, date, date);
System.out.println("Show time in 12 hour format, remove additional arguments by referencing index");
System.out.printf("%1$tH:%1$tM:%1$tS %1$tp %1$tL %1$tN %1$tz %n", date);

These statements produce the following output:

Use t or T, same result
14:06:22
14:06:22

Show time in 12 hour format
02:06:22 PM

Build Date by position
time is 14:06:22

Show time in 12 hour format, remove additional arguments by referencing index
14:06:22 pm 900 900000000 -0400 

Note in the last example, we only pass one argument, and then reference it by index. We can also use < to use the previous argument.

For example:

Date date = new Date();
System.out.println("Show time in 12 hour format, remove additional arguments by referencing index");
System.out.printf("%1$tH:%1$tM:%1$tS %1$tp %1$tL %1$tN %1$tz %n", date);
System.out.println("Same Result as above, but using < instead of $");
System.out.printf("%1$tH:%<tM:%<tS %<tp %<tL %<tN %<tz %n", date);

These statements produce the following output:

Show time in 12 hour format, remove additional arguments by referencing index
14:52:56 pm 105 105000000 -0400 
Same Result as above, but using < instead of $
14:52:56 pm 105 105000000 -0400 

Date Formatting

For date values, we also use the %t or %T Format Specifier, but with different Conversion characters.

The following conversion characters are used for formatting Date values.

The following statements demonstrate date formatting:

Date date = new Date();
System.out.printf("%1$tA, %1$tB %1$tY %n", date);
System.out.printf("%1$td/%1$tm/%1$ty %n", date);
System.out.printf("%1$td/%1$tm/%1$tY %n", date);
System.out.printf("%s %tB %<te, %<tY%n", "Current date: ", date);
System.out.printf("%s %tb %<te, %<ty%n", "Current date: ", date);
System.out.printf("%tD%n", date);

These statements produce the following output:

Wednesday, October 2024 
16/10/24 
16/10/2024 
Current date:  October 16, 2024
Current date:  Oct 16, 24
10/16/24

Datetime Formatting

For datetime values, we also use the %t or %T Format Specifier. We can use a combination of the conversion characters we’ve looked at for time and date.

There are a couple conversion characters available for datetime formatting. The values are as follows:

The following statements demonstrate the formatting of Datetime values.

Date date = new Date();
System.out.printf("%tF %n", date);
System.out.printf("%tc %n", date);
System.out.printf(Locale.US, "%tc %n", date);
System.out.printf(Locale.UK, "%tc %n", date);
System.out.printf(Locale.GERMAN, "%tc %n", date);
System.out.printf(Locale.CHINESE, "%tc %n", date);

These statements generate the following output:

2024-10-16 
Wed Oct 16 15:04:45 EDT 2024 
Wed Oct 16 15:04:45 EDT 2024 
Wed Oct 16 15:04:45 GMT-04:00 2024 
Mi. Okt. 16 15:04:45 EDT 2024 
周三 10月 16 15:04:45 EDT 2024 

Conclusion

As you can see we have a lot of flexibility for formatting values using the printf() method in Java.

The examples used in this tutorial are available in my Github repository here.