Java String Formatting — format(), printf() & Text Blocks

Java provides several ways to format strings — from classic printf()-style format specifiers to modern text blocks. This chapter covers them all.

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String.format()

Creates a formatted string without printing it:

String msg = String.format("Hello, %s! You are %d years old.", "Alice", 30);
// "Hello, Alice! You are 30 years old."

Common Format Specifiers

Specifier	Type	Example	Output
%s	String	format("%s", "Hi")	Hi
%d	Integer	format("%d", 42)	42
%f	Float/Double	format("%f", 3.14)	3.140000
%.2f	Float (2 decimal)	format("%.2f", 3.14159)	3.14
%b	Boolean	format("%b", true)	true
%c	Character	format("%c", 'A')	A
%n	Newline (platform)	format("line1%nline2")	line1↵line2
%x	Hex	format("%x", 255)	ff
%o	Octal	format("%o", 8)	10
%%	Literal %	format("100%%")	100%

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printf() — Print Formatted

Same format specifiers, but prints directly to console:

System.out.printf("Name: %s, Score: %d%n", "Bob", 95);
// Name: Bob, Score: 95

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Width, Padding, and Alignment

Right-Aligned (Default)

System.out.printf("|%10s|%n", "Java");
// |      Java|

Left-Aligned

System.out.printf("|%-10s|%n", "Java");
// |Java      |

Zero-Padded Numbers

System.out.printf("|%010d|%n", 42);
// |0000000042|

Practical Table Formatting

System.out.printf("%-15s %5s %10s%n", "Product", "Qty", "Price");
System.out.printf("%-15s %5d %10.2f%n", "Widget", 100, 9.99);
System.out.printf("%-15s %5d %10.2f%n", "Gadget", 50, 24.95);
System.out.printf("%-15s %5d %10.2f%n", "Doohickey", 200, 1.50);

Output:

Product           Qty      Price
Widget            100       9.99
Gadget             50      24.95
Doohickey         200       1.50

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Argument Index

Reference arguments by position (1-indexed):

String.format("%1$s has %2$d cats and %2$d dogs", "Alice", 3);
// "Alice has 3 cats and 3 dogs"

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Formatting Dates

import java.time.LocalDateTime;

LocalDateTime now = LocalDateTime.now();

System.out.printf("Date: %tF%n", now);    // 2026-04-20
System.out.printf("Time: %tT%n", now);    // 14:30:45
System.out.printf("Day:  %tA%n", now);    // Monday
System.out.printf("Full: %tc%n", now);    // Mon Apr 20 14:30:45 ...

Specifier	Meaning	Example
%tF	ISO date	2026-04-20
%tT	24h time	14:30:45
%tD	US date	04/20/26
%tA	Day name	Monday
%tB	Month name	April

Tip: For serious date formatting, use DateTimeFormatter (covered in the Dates & Time chapter).

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formatted() — Java 15+

Instance method on String:

String msg = "Hello, %s! You scored %d%%".formatted("Alice", 95);
// "Hello, Alice! You scored 95%"

Equivalent to String.format() but reads more fluently.

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Text Blocks — Java 13+ (Standard in 15)

Multi-line strings without escape characters:

String json = """
        {
            "name": "Alice",
            "age": 30,
            "city": "New York"
        }
        """;

Rules

1. Opening """ must be followed by a newline.
2. Closing """ position determines indentation stripping.
3. Common leading whitespace is removed automatically.

Text Blocks with Format

String html = """
        <html>
            <body>
                <h1>%s</h1>
                <p>Score: %d</p>
            </body>
        </html>
        """.formatted("Alice", 95);

Escape Sequences in Text Blocks

Escape	Meaning
\n	Newline
\s	Space (prevents trailing space stripping)
\ at end of line	Line continuation (no newline)

String single = """
        This is a very long \
        line that continues.""";
// "This is a very long line that continues."

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MessageFormat (Localisation)

import java.text.MessageFormat;

String msg = MessageFormat.format(
    "On {0,date}, {1} scored {2,number,integer} points.",
    new java.util.Date(), "Alice", 42
);

Useful for internationalised applications.

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Common Mistakes

Mistake	Problem	Fix
Using \n instead of %n	Not platform-independent	Use %n in format strings
Wrong specifier type	IllegalFormatConversionException	Match %d with int, %s with String
Forgetting %% for literal %	MissingFormatArgumentException	Use %%
Text block indentation	Unexpected leading spaces	Align closing """

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Key Takeaways

1. String.format() and printf() use the same format specifiers (%s, %d, %f, etc.).
2. Control width, alignment, and padding: %-10s (left), %010d (zero-padded).
3. Use %n for platform-independent newlines.
4. Text blocks (Java 13+) simplify multi-line strings — great for JSON, SQL, HTML.
5. Use .formatted() (Java 15+) for a fluent alternative to String.format().

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What’s Next?

Next: Regular Expressions — pattern matching, the Pattern and Matcher classes, and common regex patterns.