NextLine consumes from the input cursor to the next \n

• nextLine consumes from the input cursor to the next \n .

• Scanner input = new Scanner(new File(""));
• while (input.hasNextLine()) {
• String line = input.nextLine();
• 
  ;
• }

public class Hours {

• public class Hours {

• public static void main(String[] args)

• throws FileNotFoundException {

• Scanner input = new Scanner(new File("hours.txt"));

• while (input.hasNextLine()) {

• String line = input.nextLine();

• int id = line.nextInt(); // e.g. 456

• String name = line.nextLine(); // e.g. "Greg"

• double sum = 0.0;

• int count = 0;

• while (line.hasNextDouble()) {

• sum = sum + line.nextDouble();

• count++;

• }

• double average = sum / count;

• System.out.println(name + " (ID#" + id + ") worked " +

• sum + " hours (" + average + " hours/day)");

• }

• }

• }

public class Hours {

• public class Hours {

• public static void main(String[] args)

• throws FileNotFoundException {

• Scanner input = new Scanner(new File("hours.txt"));

• while (input.hasNextLine()) {

• String line = input.nextLine();

• Scanner tokens = new Scanner(line);

• int id = tokens.nextInt(); // e.g. 456

• String name = tokens.next(); // e.g. "Greg"

• double sum = 0.0;

• int count = 0;

• while (tokens.hasNextDouble()) {

• sum = sum + tokens.nextDouble();

• count++;

• }

• double average = sum / count;

• System.out.println(name + " (ID#" + id + ") worked " +

• sum + " hours (" + average + " hours/day)");

• }

• }

• }

A String Scanner can tokenize each line of a file.

• A String Scanner can tokenize each line of a file.

• Scanner input = new Scanner(new File("filename"));
• while (input.hasNextLine()) {
• String line = input.nextLine();
• Scanner tokens = new Scanner(line);
• 
  ;
• }

collapseSpaces exercise

• Write a method collapeSpaces that accepts a file Scanner and writes that file's text to the console, with multiple spaces/tabs between words reduced to a single space.

Exercise solution

• public static void collapseSpaces(Scanner input) {

• while (input.hasNextLine()) {

• String line = input.nextLine();

• Scanner words = new Scanner(line);

• if (words.hasNext()) {

• System.out.print(words.next());

• while (words.hasNext()) {

• System.out.print(" " + words.next());

• }

• }

• System.out.println();

• }

• }

leetSpeak exercise

• Write a method leetSpeak that accepts two parameters:

• a Scanner representing an input file, and
• a PrintStream representing an output file.

• Convert the input file's text to "leet speak", where various letters are replaced by other letters/numbers. Output the leet version of the text to the given output file.

• Preserve the original line breaks from the input.
• Wrap each word of input in parentheses.

• // example call

• Scanner input = new Scanner(new File("lincoln.txt"));

• PrintStream output = new PrintStream(new File("leet.txt"));

• leetSpeak(input, output);

1337-speak replacements

Exercise solution

• public static void leetSpeak(Scanner input, PrintStream output) {

• while (input.hasNextLine()) {

• String line = input.nextLine();

• Scanner lineScanner = new Scanner(line);

• while (lineScanner.hasNext()) {

• String word = lineScanner.next();

• word = word.replace("o", "0");

• word = word.replace("l", "1");

• word = word.replace("e", "3");

• word = word.replace("a", "4");

• word = word.replace("t", "7");

• if (word.endsWith("s")) {

• word = word.substring(0, word.length() - 1) + "Z";

• }

• output.print("(" + word + ") ");

• }

• output.println(); // preserve line breaks

• }

• }

Using nextLine in conjunction with the token-based methods on the same Scanner can cause bad results.

• Using nextLine in conjunction with the token-based methods on the same Scanner can cause bad results.

• 23 3.14 Joe "Hello world" 45.2 19
• You'd think you could read 23 and 3.14 with nextInt and nextDouble, then read Joe "Hello world" with nextLine .
• System.out.println(input.nextInt()); // 23
• System.out.println(input.nextDouble()); // 3.14
• System.out.println(input.nextLine()); //
• But the nextLine call produces no output! Why?

Don't read both tokens and lines from the same Scanner:

• Don't read both tokens and lines from the same Scanner:

• 23 3.14 Joe "Hello world" 45.2 19

• input.nextInt() // 23 23\t3.14\nJoe\t"Hello world"\n\t\t45.2 19\n ^

• input.nextDouble() // 3.14 23\t3.14\nJoe\t"Hello world"\n\t\t45.2 19\n ^

• input.nextLine() // "" (empty!) 23\t3.14\nJoe\t"Hello world"\n\t\t45.2 19\n ^

• input.nextLine() // "Joe\t\"Hello world\"" 23\t3.14\nJoe\t"Hello world"\n\t\t45.2 19\n ^

Scanner console = new Scanner(System.in);

• Scanner console = new Scanner(System.in);
• System.out.print("Enter your age: ");
• int age = console.nextInt();
• System.out.print("Now enter your name: ");
• String name = console.nextLine();
• System.out.println(name + " is " + age + " years old.");

• Log of execution (user input underlined):

• Enter your age: 12
• Now enter your name: Sideshow Bob
• is 12 years old.

• Why?

• Overall input: 12\nSideshow Bob
• After nextInt(): 12\nSideshow Bob ^
• After nextLine(): 12\nSideshow Bob ^