Java String format()

class Main {
  public static void main(String[] args) {

    String str = "Java";

    // format string 
    String formatStr = String.format("Language: %s", str);

    System.out.println(formatStr);
  }
}

// Output: Language: Java

format() Syntax

The syntax of the String format() method is:

String.format(String str, Object... args)

Here,

• format() is a static method. We call the format() method using the class name String.
• str is a string that is to be formatted
• ... in the above code signifies you can pass more than one object to format().

format() Parameters

The format() method takes two parameters.

• format - a format string
• args - 0 or more arguments

format() Return Value

• returns a formatted string

Example 1: Java String format()

class Main {
  public static void main(String[] args) {
    String language = "Java";
    int number = 30;
    String result;

    // format object as a string
    result = String.format("Language: %s", language);

    System.out.println(result);  // Language: Java

    // format number as a hexadecimal number
    result = String.format("Hexadecimal Number: %x", number);  // 1e

    System.out.println(result); // Hexadecimal Number: 1e
  }
}

In the above program, notice the code

result = String.format("Language: %s", language);

Here, "Language: %s" is a format string.

%s in the format string is replaced with the content of language. %s is a format specifier.

Similarly, %x is replaced with the hexadecimal value of number in String.format("Number: %x", number).

Format Specifiers

Here are the commonly used format specifiers:

Example 2: String Formatting of Numbers

class Main {
  public static void main(String[] args) {
    int n1 = 47;
    float n2 = 35.864f;
    double n3 = 44534345.76d;

    // format as an octal number
    System.out.println(String.format("n1 in octal: %o", n1));  // 57


    // format as hexadecimal numbers
    System.out.println(String.format("n1 in hexadecimal: %x", n1));  // 2f
    System.out.println(String.format("n1 in hexadecimal: %X", n1));  // 2F

    // format as strings
    System.out.println(String.format("n1 as string: %s", n1));  // 47
    System.out.println(String.format("n2 as string: %s", n2));  // 35.864

    // format in scientific notation
    System.out.println(String.format("n3 in scientific notation: %g", n3)); // 4.45343e+07
  }
}

Output

n1 in octal: 57
n1 in hexadecimal: 2f
n1 in hexadecimal: 2F
n1 as string: 47
n2 as string: 35.864
n3 in scientific notation: 4.45343e+07

Example 3: String format with multiple format specifiers

You can use more than one format specifier in the format string.

// using more than one format specifiers
// in a format string
class Main {
  public static void main(String[] args) {
    int n1 = 47;
    String text = "Result";

    System.out.println(String.format("%s\nhexadecimal: %x", text, n1));


  }
}

Output

Result
hexadecimal: 2f

Here, %s is replaced with the value of text. Similarly, %o is replaced with the hexadecimal value of n1.

Example 4: Formatting of Decimal Numbers

class Main {
  public static void main(String[] args) {

    float n1 = -452.534f;
    double n2 = -345.766d;

    // format floating-point as it is
    System.out.println(String.format("n1 = %f", n1)); // -452.533997

    System.out.println(String.format("n2 = %f", n2)); // -345.766000

    // show up to two decimal places
    System.out.println(String.format("n1 = %.2f", n1)); // -452.53

    System.out.println(String.format("n2 = %.2f", n2)); // -345.77
  }
}

Output

n1 = -452.533997
n2 = -345.766000
n1 = -452.53
n2 = -345.77

Note: When we format -452.534 using %f, we are getting -452.533997. It is not because of the format() method. Java doesn't return the exact representation of floating-point numbers.

When %.2f format specifier is used, format() gives two numbers after the decimal point.

Example 5: Padding Numbers With Spaces and 0

// using more than one format specifiers
// in a format string
class Main {
  public static void main(String[] args) {
    int n1 = 46, n2 = -46;
    String result;

    // padding number with spaces
    // the length of the string will be 5
    result = String.format("|%5d|", n1); // |   46|

    System.out.println(result);

    // padding number with numbers 0
    // the length of the string will be 5
    result = String.format("|%05d|", n1); // |00046|

    System.out.println(result);

    // using signs before numbers
    result = String.format("%+d", n1); // +46

    System.out.println(result);

    result = String.format("%+d", n2); // -46

    System.out.println(result);

    // enclose negative number within parenthesis
    // and removing the sign
    result = String.format("%(d", n2); // (46)

    System.out.println(result);
  }
}

Example 6: Using 0x and 0 before Hexadecimal and Octal

// using 0x before hexadecimal
// using 0 before octal
class Main {
  public static void main(String[] args) {
    int n = 46;

    System.out.println(String.format("%#o", n)); // 056
    System.out.println(String.format("%#x", n)); // 0x2e

  }
}

Java String format() with Locale

The String format() method also has another syntax if you have to work with the specified locale.

String.format(Locale l,
              String format, 
              Object... args)

Example 7: Using GERMAN Locale in format()

// to use Locale
import java.util.Locale;

class Main {
  public static void main(String[] args) {
    int number = 8652145;
    String result;

    // using the current locale
    result = String.format("Number: %,d", number);

    System.out.println(result);

    // using the GERMAN locale as the first argument
    result = String.format(Locale.GERMAN, "Number in German: %,d", number);

    System.out.println(result);
  }
}

Output

Number: 8,652,145
Number in German: 8.652.145

Note: In Germany, integers are separated by . instead of ,.