Java基础之一组有用的类——使用Scanner对象（TryScanner)

控制台程序。

java.util.Scanner类定义的对象使用正则表达式来扫描来自各种源的字符输入，并把输入显示为各种基本类型的一系列标记或者显示为字符串。

默认情况下，Scanner对象读取标记时，假定它们用空白分隔开。对于空白对应的任意字符,Character类中的isWhitespace()方法都返回true。因此，读取标记时，要跳过分隔符，找到不是分隔符的字符，然后尝试以要求的方式解释那些不是分隔符的字符序列。

 import java.util.Scanner;
 import java.util.InputMismatchException;

 public class TryScanner {
   public static void main(String[] args) {
     Scanner kbScan = new Scanner(System.in);                           // Create the scanner
     int selectRead = 1;                                                // Selects the read operation
     final int MAXTRIES = 3;                                            // Maximum attempts at input
     int tries = 0;                                                     // Number of input attempts

     while(tries<MAXTRIES) {
       try {
         switch(selectRead) {
           case 1:
           System.out.print("Enter an integer: ");
           System.out.println("You entered: "+ kbScan.nextLong());
           ++selectRead;                                                // Select next read operation
           tries = 0;                                                   // Reset count of tries

           case 2:
           System.out.print("Enter a floating-point value: ");
           System.out.println("You entered: "+ kbScan.nextDouble());
           ++selectRead;                                                // Select next read operation
           tries = 0;                                                   // Reset count of tries

           case 3:
           System.out.print("Enter a boolean value(true or false): ");
           System.out.println("You entered: "+ kbScan.nextBoolean());
         }
         break;
       } catch(InputMismatchException e) {
           String input = kbScan.next();
           System.out.println("\""+ input +"\" is not valid input.");
           if(tries<MAXTRIES) {
             System.out.println("Try again.");
           } else {
             System.out.println(" Terminating program.");
             System.exit(1);
          }
       }
     }
   }
 }