Here a few examples:

(The output is shown within double quotes in the embedded comment)

Note : System.out.format() = System.out.printf()

import java.util.Calendar;
import java.util.Locale;

public class TestFormat {

    public static void main(String[] args) {
      long n = 461012;
      System.out.format("%d%n", n);      //  -->  "461012"
      System.out.format("%08d%n", n);    //  -->  "00461012"
      System.out.format("%+8d%n", n);    //  -->  " +461012"
      System.out.format("%,8d%n", n);    // -->  " 461,012"
      System.out.format("%+,8d%n%n", n); //  -->  "+461,012"

      double pi = Math.PI;

      System.out.format("%f%n", pi);       // -->  "3.141593"
      System.out.format("%.3f%n", pi);     // -->  "3.142"
      System.out.format("%10.3f%n", pi);   // -->  "     3.142"
      System.out.format("%-10.3f%n", pi);  // -->  "3.142"
      System.out.format(Locale.FRANCE,
                        "%-10.4f%n%n", pi); // -->  "3,1416"

      Calendar c = Calendar.getInstance();
      System.out.format("%tB %te, %tY%n", c, c, c); // -->  "May 29, 2006"

      System.out.format("%tl:%tM %tp%n", c, c, c);  // -->  "2:34 am"

      System.out.format("%tD%n", c);    // -->  "05/29/06"
    }
}

(source)

As per the Formatter docs, %d is a conversion for an integral value, which wouldn't work for doubles. You'll want to convert them to integers. Why would you represent month, day, and year as floating point numbers, anyway? You'd be much better off using a Date and using an appropriate formatter for date values.

If you must use doubles for those values, you'll want %f instead of %d.

http://docs.oracle.com/javase/7/docs/api/java/util/Formatter.html http://docs.oracle.com/javase/7/docs/api/java/io/PrintStream.html#printf%28java.lang.String,%20java.lang.Object...%29

Hi Evan, Method println() prints String on new line. You can concatenate multiple items with +. Method printf() prints formatted output in the way you mentioned: java System.out.printf("Hey %s the movie starts at 7", friend); Which looks better than something like this, especially for big output Strings. java System.out.println("hey" + friend + "the movie starts at 7"); So it is good to avoid confusion when you are printing big Strings. Pretty good explanation is also here: https://teamtreehouse.com/community/difference-between-systemoutprintf-and-systemoutprintln

println is used when you want to create a new line with just simple text or even text containing concatenation. ("Hello " + "World" = "Hello World.") printf is used when you want to format your string. This will clean up any concatenation. For a simple example -> ("Hello, " + username + "! How are you?") could easily be cleaned up a bit by using ("Hello, %s! How are you?", username). It's up to you really when you want to use this. I would definitely recommend it if you are using multiple variables. In that case you would use multiple conversions in your string. Please feel free to read up on the Formatter Documentation (https://docs.oracle.com/javase/7/docs/api/java/util/Formatter.html) as it will help you understand it better and it provides a full list of available conversion characters.