kbr.java

《A first book of java》by Gary J.Bronson 北大出版社

// This class can be used to enter single character and numerical 
// values at the Keyboard, as described in Appendix G of the text.

import java.io.*;   // needed to access input stream classes
public class KBR
{
  
  // This method sets up the basic keyboard input streams
  // and reads a line of characters from the keyboard.
  // It returns all characters entered as a string, with any
  // entered whitespace included.
  public static String readData()
  throws java.io.IOException
  {
      // set up the first input stream, which is
      // needed for conversion capabilities	
    InputStreamReader isr = new InputStreamReader(System.in);
      // set up a buffered stream, which is
      // needed to access readLine()
    BufferedReader br = new BufferedReader(isr);
 
    return br.readLine();  // read and return the entered data
  }

  // This method captures and returns the first character entered 
  // at the keyboard. If no characters are entered, it will return 
  // the code for the ENTER key.
  public static char readChar()
  throws java.io.IOException
  {
    String inString = null;
    char key;

    inString = readData();
    if (inString.length() == 0)
      key = 0x000D;   // Unicode value for the Enter key
    else
      key = inString.charAt(0);  // 1st character entered
    return key;
    
  }

  // This method attempts to convert the characters entered at the 
  // keyboard to an integer value. If the conversion cannot 
  // be done, an error message is displayed and the read is 
  // continued until a valid integer is entered.
  public static int readInt()
  throws java.io.IOException
  {
    int inValue = 0;  // must initialize the variable
    boolean validNumber = false;
    String inString = null;
   
    while(!validNumber)
    {
      try
      {
        inString = readData();
        inValue = Integer.parseInt(inString.trim());
        validNumber = true;
      }
      catch(NumberFormatException e)
      {
        System.out.println("  The value you entered is not valid. ");
        System.out.println("  Please enter only numeric digits.");
        System.out.print("Enter an integer value: ");
      }
    }
    return inValue;   
  }
 
  // This method attempts to convert the characters entered at the 
  // keyboard to a long integer value. If the conversion cannot 
  // be done, an error message is displayed and the read is 
  // continued until a valid long integer is entered.
  public static long readLong()
  throws java.io.IOException
  {
    long inValue = 0L;  // must initialize the variable
    boolean validNumber = false;
    String inString = null;
   
     while(!validNumber)
    {
      try
      {
        inString = readData();
        inValue = Long.parseLong(inString.trim());
        validNumber = true;
      }
      catch(NumberFormatException e)
      {
        System.out.println("  The value you entered is not valid. ");
        System.out.println("  Please enter only numeric digits.");
        System.out.print("Enter a long integer value: ");
      }
    }
    return inValue;   
  }

  // This method attempts to convert the characters entered at the 
  // keyboard to a float value. If the conversion cannot 
  // be done, an error message is displayed and the read is 
  // continued until a valid float is entered.
  public static float readFloat()
  throws java.io.IOException
  {
    float inValue = 0F;  // must initialize the variable
    boolean validNumber = false;
    String inString = null;
   
     while(!validNumber)
    {
      try
      {
        inString = readData();
        inValue = Float.parseFloat(inString.trim());
        validNumber = true;
      }
      catch(NumberFormatException e)
      {
        System.out.println("  The value you entered is not valid. ");
        System.out.println("  Please enter only numeric digits");
        System.out.println("  and, at most, a single decimal point.");
        System.out.print("Enter a float value: ");
      }
    }
    return inValue;   
  }

  // This method attempts to convert the characters entered at the 
  // keyboard to a double value. If the conversion cannot 
  // be done, an error message is displayed and the read is 
  // continued until a valid double is entered.
  public static double readDouble()
  throws java.io.IOException
  {
    double inValue = 0;  // must initialize the variable
    boolean validNumber = false;
    String inString = null;
   
     while(!validNumber)
    {
      try
      {
        inString = readData();
        inValue = Double.parseDouble(inString.trim());
        validNumber = true;
      }
      catch(NumberFormatException e)
      {
        System.out.println("  The value you entered is not valid. ");
        System.out.println("  Please enter only numeric digits");
        System.out.println("  and, at most, a single decimal point.");
        System.out.print("Enter a double value: ");
      }
    }
    return inValue;   
  }
}