scanner

Une classe a fait son apparition dans le package java.util dans la version 1.5.0 de java

Cette classe s'interface parfaitement avec des flux de lecture pour y permettre une lecture puissante et pratique !

A simple text scanner which can parse primitive types and strings using regular expressions.

A Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace. The resulting tokens may then be converted into values of different types using the various next methods.

For example, this code allows a user to read a number from System.in:

     Scanner sc = new Scanner(System.in);
int i = sc.nextInt();

As another example, this code allows long types to be assigned from entries in a file myNumbers:

      Scanner sc = new Scanner(new File("myNumbers"));
while (sc.hasNextLong()) {
long aLong = sc.nextLong();
}

The scanner can also use delimiters other than whitespace. This example reads several items in from a string:

     String input = "1 fish 2 fish red fish blue fish";
Scanner s = new Scanner(input).useDelimiter("\\s*fish\\s*");
System.out.println(s.nextInt());
System.out.println(s.nextInt());
System.out.println(s.next());
System.out.println(s.next());
s.close();

prints the following output:

     1
2
red
blue

The same output can be generated with this code, which uses a regular expression to parse all four tokens at once:

     String input = "1 fish 2 fish red fish blue fish";
Scanner s = new Scanner(input);
s.findInLine("(\\d+) fish (\\d+) fish (\\w+) fish (\\w+)");
MatchResult result = s.match();
for (int i=1; i<=result.groupCount(); i++)
System.out.println(result.group(i);
s.close();

The default whitespace delimiter used by a scanner is as recognized by Character.isWhitespace.

A scanning operation may block waiting for input.

The next() and hasNext() methods and their primitive-type companion methods (such as nextInt() and hasNextInt()) first skip any input that matches the delimiter pattern, and then attempt to return the next token. Both hasNext and next methods may block waiting for further input. Whether a hasNext method blocks has no connection to whether or not its associated next method will block.

The findInLine(java.lang.String), findWithinHorizon(java.lang.String, int), and skip(java.util.regex.Pattern) methods operate independently of the delimiter pattern. These methods will attempt to match the specified pattern with no regard to delimiters in the input and thus can be used in special circumstances where delimiters are not relevant. These methods may block waiting for more input.

When a scanner throws an InputMismatchException, the scanner will not pass the token that caused the exception, so that it may be retrieved or skipped via some other method.

Depending upon the type of delimiting pattern, empty tokens may be returned. For example, the pattern "\\s+" will return no empty tokens since it matches multiple instances of the delimiter. The delimiting pattern "\\s" could return empty tokens since it only passes one space at a time.

A scanner can read text from any object which implements the Readable interface. If an invocation of the underlying readable's Readable.read(java.nio.CharBuffer) method throws an IOException then the scanner assumes that the end of the input has been reached. The most recent IOException thrown by the underlying readable can be retrieved via the ioException() method.

When a Scanner is closed, it will close its input source if the source implements the Closeable interface.

A Scanner is not safe for multithreaded use without external synchronization.

Unless otherwise mentioned, passing a null parameter into any method of a Scanner will cause a NullPointerException to be thrown.

A scanner will default to interpreting numbers as decimal unless a different radix has been set by using the useRadix(int) method.


                                                                                              Utilisation

 

Regardons les constructeurs :

Scanner(File source)

Scanner(File source, String charsetName)

Scanner(InputStream source)

Scanner(InputStream source, String charsetName)

Scanner(Readable source)

Scanner(ReadableByteChannel source)

Scanner(ReadableByteChannel source, String charsetName)

Scanner(String source)

 

On se rend vite compte que cette classe peu lire dans n?importe quoi !

Tentons une expérience.

Alors pourquoi pas ? Essayons un petit programme tout bête qui affiche ce qu?écris l?utilisateur:

 

import java.util.Scanner;

 

public class Essai {

            public static void main(String[] args) {

                        Scanner sc = new Scanner(System.in);

                        String s = "";

                        while(s.compareTo("ok")!=0){

                        s = sc.nextLine();

                        System.out.println(s);

                        }

 

            }

}

Miracle ca marche !!! Simple non ?

Maintenant je ne sais pas vous mais un constructeur qui m?as beaucoup étonné est

Scanner(String)

 

Essayons quelque chose avec les méthodes disponibles :

 

import java.util.Scanner;

 

public class Essai {

            public static void main(String[] args) {

                        String s = "Thomas Sanchez 16";

                        Scanner sc = new Scanner(s);

                        System.out.println("prenom : " + sc.next() + "\nnom : " + sc.next()

                                               + "\nage : " + sc.nextInt());

            }

}

Cool non ?

 

Bon cette classe a l?air bien mais fait-elle des merveilles pour lire un fichier aussi ?

Essayons :

 

import java.io.File;

import java.io.FileNotFoundException;

import java.util.Scanner;

 

public class Essai {

            public static void main(String[] args) {

                       

                        Scanner sc;

                        try {

                                   sc = new Scanner(new File("essai.txt"));

                                   while(sc.hasNext())

                                               System.out.println(sc.nextLine());

                        } catch (FileNotFoundException e) {

                                               e.printStackTrace();

                        }

           

            }

}


Et hop voila le fichier lu !!

Bon ca pourrais durer longtemps pour que je vous montre toute les utilisations possible....a vous de fouiller plus en detail!

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