Java's printf()

printf() provides a more direct way of formatting strings with values only known at run-time. Consider the following comparison of println() vs. printf():

public class Tester {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
	System.out.print("Enter a value: ");
	double userInput = in.nextDouble();
 
	System.out.println("(With println) You entered: " + userInput);
	System.out.printf("(With printf) You entered: %f\n", userInput);
  }
}

Let’s deconstruct our printf(). First and foremost, the method itself is called printf, meaning “print format”. printf() has two distinct behaviors, compared to println():

• printf() does not append a new line character automatically
• printf() does allow variable substitution

You will notice the lack of a new line pretty quickly if you have anything printed after a printf() statement. We can insert our own new line any place we please by using the %n or \n flag. These flags are equivalent, but “backslash n” is the widely used code, whereas “percent n” is the Java specific flag. Both are recognized by Java. Note: the new line character must be placed within the "". You will receive a compile error otherwise.

Variable substitution is the second benefit afforded by printf(). Here’s the basic format:

double variableOfDoubleOrFloatingType = 42;
System.out.printf("%f <- your variable is substituted here!", variableOfDoubleOrFloatingType);

To have printf() substitute our variable, we must first use the correct flag. Each primitive has a corresponding flag built into Java:

• s = String
• d = int
• f = float or double
• t = date/time
• b = boolean
• c = char

The format for a flag is as follows:

%[flags][width][.precision]conversion-character

Please visit Baeldung for a breakdown of each flag.