CODEWITHSUNDEEP
javastringformatstring-formatting
theineffablebob
theineffablebob

Reputation: 319

What does "%1$#" mean when used in String.format (Java)?

Language is Java. What does the %1$# mean in...

static String padright (String str, int num) {
   return String.format("%1$#" + num + "str", str);
}

In the Java API, String.format() is used in this way:

public static String format(String format, Object... args)

So I think %1$# is a format specifier.

%[flags][width][.precision][argsize]typechar is the template.

Is that right?

Upvotes: 27

Views: 56998

Answers (2)

Jayasurya
Jayasurya

Reputation: 137

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

%1$s

% is mandatory for format 1$ is the first argument passed 2$ is the second... etc s here is the string type conversion (result is obtained by invoking arg.toString())

Example with multiple string arguments:

String firstName = "John";
String lastName = "Doe";
String formattedString = String.format("My name is %1$s %2$s.", firstName, lastName);
System.out.println(formattedString);

Output:

My name is John Doe.

In this example, %1$s is used to reference the first string argument (firstName), and %2$s is used to reference the second string argument (lastName).

Example with multiple numeric arguments:

int num1 = 10;
double num2 = 3.14159;
String formattedString = String.format("The value of num1 is %1$d and the value of num2 is %2$.2f.", num1, num2);
System.out.println(formattedString);

Output:

The value of num1 is 10 and the value of num2 is 3.14.

In this example, %1$d is used to reference the first numeric argument (num1), and %2$.2f is used to reference the second numeric argument (num2) and format it as a floating-point value with two decimal places.

Example with mixed arguments:

String name = "John";
int age = 30;
double height = 1.80;
String formattedString = String.format("%1$s is %2$d years old and is %3$.2f meters tall.", name, age, height);
System.out.println(formattedString);

Output:

John is 30 years old and is 1.80 meters tall.

In this example, %1$s is used to reference the first string argument (name), %2$d is used to reference the second numeric argument (age), and %3$.2f is used to reference the third numeric argument (height) and format it as a floating-point value with two decimal places.

Upvotes: 2

manojlds
manojlds

Reputation: 301327

Template:

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

The optional argument_index is a decimal integer indicating the position of the argument in the argument list. The first argument is referenced by "1$", the second by "2$", etc.

The optional flags is a set of characters that modify the output format. The set of valid flags depends on the conversion.

The optional width is a decimal integer indicating the minimum number of characters to be written to the output.

The optional precision is a non-negative decimal integer usually used to restrict the number of characters. The specific behavior depends on the conversion.

The required conversion is a character indicating how the argument should be formatted. The set of valid conversions for a given argument depends on the argument's data type.

%1$ refers to the first substitution. In this case the string str. # is flag which says the result should use a conversion-dependent alternate form.

http://download.oracle.com/javase/1.5.0/docs/api/java/util/Formatter.html

Upvotes: 43

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