converter.java

Java经典例程 从外国一大学计算机教授出版物下载的代码 经典

import java.io.*;
import javagently.*;
import java.util.*;
import myutilities.*;

class Converter {

  /* The Converter Program     by J M Bishop  Dec 1998
   * ---------------------     updated June 2000
   * Keeps the exchange rates from one currency into
   * many others and enables currency purchases to be
   * estimated.
   *
   * Illustrates the use of hash tables.
   */

  Display display = new Display ("Currency Converter");
  Hashtable table = new Hashtable();

  Converter () throws IOException {
    initialise();
    readIn();
    echo();
    transactions();
  }


    // read in each line of data and store in
    // the hash table with country as key

    void initialise () {
      display.println("Currency Converter\n"+
                      "==================");
      display.prompt("Rates file", "rates.dat");
      display.ready("Press ready when the file is ok");
    }

    void readIn() throws IOException {
      Rates rate;
      String filename = display.getString("Rates file");
      Stream fin = Filer.open(filename);
      try {
        for (int i = 0; ; i++) {
          rate = new Rates();
          rate.setRate(fin);
          table.put(rate.country, rate);
        }
      }
      catch (EOFException e) {
        display.println("Data read in and stored\n");
      }
    }

    void echo() {
      display.println("In the table");
      int i = 1;
      for (Enumeration e = table.keys(); e.hasMoreElements(); i++) {
        String country = (String)e.nextElement();
        display.println(country);
      }
    }

    void transactions () {
      display.prompt("Country", "American");
      display.prompt("Amount", 1000);
      String country;
      double amount;
      String c;
      Rates r;

      while (true) {
        display.println("Scroll up to see countries");
        display.ready("Enter country and amount and press ready");
        c = display.getString("Country");
        if (table.containsKey(c)) {
          amount = display.getDouble("Amount");
          r = (Rates) table.get(c);
          display.println( Stream.format(amount,6,2) +" ZAR in "+c+" "
              +r.currency+" is "+
              Stream.format(amount * r.conversion,6,2)+"\n");
        }
        else {
           display.println("Sorry, country "+c+" not in table\n");
        }
      } // while
    } // transactions

    public static void main(String[] args) throws IOException {
      Converter data = new Converter ();
    }

  } // class Converter