The class Scanner allows you easily to associate a variable with one of a number of different input streams such as the keyboard, a file or a string:

0047:       Scanner tScannerKeyboard   = new Scanner(System.in);
0048:       Scanner tScannerInputFile  = new Scanner(new File("input.txt"));
0049:       Scanner tScannerSomeString = new Scanner(tSomeString);

You can then apply methods such as nextInt to read a value from the input stream. Here, an unchecked exception java.util.InputMisMatchException will be thrown if the next token is not an int.

To avoid the possibility of this exception occurring, a method like hasNextInt can be used to determine if the next value is an int, as shown in this program:

0067: import java.util.Scanner;                                    // Analyse.java
0068: public class Analyse
0069: {
0070:    public static void main(String[] pArgs)
0071:    {
0072:       Scanner tScanner = new Scanner(System.in);
0073:       System.out.print("Type in a value: ");
0074:       if (tScanner.hasNextInt()) {
0075:          int tFirst = tScanner.nextInt();
0076:          System.out.println("Got an int: " + tFirst);
0077:       }
0078:       else if (tScanner.hasNextDouble()) {
0079:          double tFirst = tScanner.nextDouble();
0080:          System.out.println("Got a double: " + tFirst);
0081:       }
0082:       else {
0083:          String tFirst = tScanner.nextLine();
0084:          System.out.println("Got a string: " + tFirst);
0085:       }
0086:    }
0087: }