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);
         }
      }
    }
  }
}