How to format a string in Java
There are many ways to format a string in Java. You can use the String.format() method, the printf() method, or the MessageFormat class for formatting strings.
The most common way of formatting a string in Java is using the String.format() method. This static method returns a formatted string using the given locale, format string, and arguments. Here is an example:
String name = "John Doe"; String str = String.format("My name is %s", name); System.out.println(str); // My name is John Doe The String.format() method also allows us to set the width, alignment, and padding of the formatted string:
String message = "Hey 👋"; // Text width String.format("|%20s|", message); // | Hey 👋| // Left justify text String.format("|%-20s|", message); // |Hey 👋 | // Maximum number of characters String.format("|%.3s|", message); // |Hey| // Max. characters with width String.format("|%20.3s|", message); // | Hey| Besides formatting, the String.format() method can also be used to convert and format other data types into a string:
String str1 = String.format("%d", 999); // Integer value String str2 = String.format("%f", 56.7); // Float value String str3 = String.format("%x", 678); // Hexadecimal value String str4 = String.format("%o", 99); // Octal value String str5 = String.format("%tc", new Date()); // Date object String str6 = String.format("%c", 'A'); // Char value System.out.println(str1); System.out.println(str2); System.out.println(str3); System.out.println(str4); System.out.println(str5); System.out.println(str6); // 999 // 56.700000 // 2a6 // 143 // Sun Oct 03 14:05:44 PKT 2021 // A // Text width String.format("|%10d|", 999); // | 999| // Justify left String.format("|%-10d|", 999); // |999 | // Pad with zeros String.format("|%010d|", 999); // |0000000999| // Positive number String.format("%+d", 999); // +999 // Thousands separator String.format("%,d", 9999999); // 9,999,999 // Enclose -ve number with parenthesis String.format("%o", 99); // (99) // Alternative Hex & Octal formatting String.format("%#x", 99); // 0x63 String.format("%#o", 99); // 0143 The argument index is an integer indicating the position of the argument in the argument list. The first argument is referenced by 1$ , the second by 2$ , and so on.
String product = "Pizza 🍕"; double price = 5.99; String str = String.format("The price of %2$s is USD %1$.2f", price, product); System.out.println(str); // The price of Pizza 🍕 is USD 5.99 With the argument index, the order of the arguments does not matter. So you can pass the arguments in any order. Another way to reference arguments by position is to use the < flag that causes the argument for the previous format specifier to be re-used:
String str = String.format("Today is %1$tB %, LocalDate.now()); System.out.println(str); // Today is October 03, 2021 String str = String.format("%2$d + %2$d = 4", 1, 2); System.out.println(str); // 2 + 2 = 4 By default, the String.format() method uses the default locale by calling the Locale.getDefault() method. To localize the formatted string, you have to pass a valid locale as the first argument, as shown below:
int number = 4566778; String withoutLocale = String.format("%,d", number); String withLocale = String.format(Locale.GERMAN, "%,d", number); System.out.println(withoutLocale); // 4,566,778 System.out.println(withLocale); // 4.566.778 Notice the additional , flag before d in the format string. This flag is used to include locale-specific grouping separators.
| Specifier | Data Type | Output |
|---|---|---|
| %a | Floating point (except BigDecimal) | Hex output of floating-point number |
| %b | Any type | “true” if non-null, “false” if null |
| %c | Character | Unicode character |
| %d | Integer (incl. byte, short, int, long, BigInt) | Decimal Integer |
| %e | Floating point | Decimal number in scientific notation |
| %f | Floating point | Decimal number |
| %g | Floating point | Decimal number, possibly in scientific notation depending on the precision and value. |
| %h | Any type | Hex String of value from hashCode() method. |
| %n | None | Platform-specific line separator. |
| %o | Integer (incl. byte, short, int, long, BigInt) | Octal number |
| %s | Any type | String value |
| %t | Date/Time (includes long, Calendar, Date, and TemporalAccessor) | %t is the prefix for date and time conversions. More formatting flags are needed after this. See the date and time conversion above. The full list can be found here |
| %x | Integer (incl. byte, short, int, long, BigInt) | Hex string |
Another way of formatting strings in Java is using the printf() method. This method prints the contents on the standard output stream and does not return anything:
System.out.printf("I am %s!%n", "John Doe"); System.out.printf("Total price is %.2f USD%n", 99.3); System.out.printf("Today date is %tD%n", LocalDate.now()); // I am John Doe! // Total price is 99.30 USD // Today date is 10/03/21 The printf() method uses the same underlying principles as the String.format() method. This is because both these methods internally use the Formatter class to format strings. Thus, everything said for String.format() also applies to the printf() method. The only difference is the return type; printf() prints the formatted string to the standard output stream (mostly console), whereas String.format() returns the formatted string. This makes String.format() more versatile as you can use the returned value in more than one way.
The String.formatted() method was introduced in Java 15 for formatting an instance of the String class using the supplied arguments. This method is equivalent to String.format() with default locale, except that it must be called on an already declared instance of String :
String str = "Date is %tD and time is %tT"; String formatted = str.formatted(LocalDate.now(), LocalTime.now()); System.out.println(formatted); // Date is 10/03/21 and time is 16:13:57 The above three methods use the Formatter class under to hood to format strings. You can use the same specifiers to format a string using any of them. They only differ on return type and whether to create an instance or not. To use the Formatter class directly, you need to instantiate a new instance by using its constructor:
Formatter formatter = new Formatter(); formatter.format("Date is %tD and time is %tT", LocalDate.now(), LocalTime.now()); System.out.println(formatter); // Date is 10/03/21 and time is 16:25:07 StringBuilder builder = new StringBuilder(); Formatter formatter = new Formatter(builder); formatter.format("Date is %tD and time is %tT", LocalDate.now(), LocalTime.now()); System.out.println(builder); // Date is 10/03/21 and time is 16:30:32 Finally, the last way of formatting strings in Java that does not use Formatter under the hood is the MessageFormat class. The MessageFormat class provides methods to create concatenated messages in a language-neutral way. It means the formatted messages will be the same regardless of the programming language used to construct them. This makes it suitable to create messages that are displayed to the end-users. The MessageFormat class takes in a set of objects, formats them, and then replaces the patterns at the appropriate places with the formatted strings. Here is an example:
String name = "John Doe"; String buy = "a coffee for $3.49"; String str = MessageFormat.format(" bought on at .", name, buy, new Date()); System.out.println(str); // John Doe bought a coffee for $3.49 on 3 October 2021 at 9:30:47 pm. As you can see above, we are using curly brackets ( <> ) called a pattern for each of the arguments instead of percentage specifiers ( % ). Let us look at the third pattern — <2, date, long>. The number 2 refers to the index of the argument that should be inserted in its place. In our case, it is a Date object. The second part, date , represents the format type of the argument. There are four top-level format types: number , date , time , and choice . The last part, long , represents the format style used to make a more specified selection. The date format type has short , medium , long , and full as format styles. The MessageFormat class also supports localization of the messages:
MessageFormat form = new MessageFormat(" price starts from ", Locale.US); System.out.println(form.format(new Object[]"Tesla", 39900>)); // Tesla price starts from $39,900.00 For a complete list of format types and format styles, visit the documentation. ✌️ Like this article? Follow me on Twitter and LinkedIn. You can also subscribe to RSS Feed.