Java:一个分数类的简单设计

package net.zj.fraction;

import java.io.IOException;

public  class Fraction {
     private  int numerator;
     private  int denominator;

     public Fraction( int numerator,  int denominator) {
       this.numerator = numerator;
       this.denominator = denominator;
    }

     public Fraction( int numerator) {
       this(numerator, 1);
    }

     public  static Fraction add(Fraction f1, Fraction f2) {
      Fraction[] fs = RCD(f1, f2);
      Fraction add =  new Fraction(fs[0].numerator + fs[1].numerator,
        fs[0].denominator);
       return simpler(add);
    }

     public  static Fraction minus(Fraction f1, Fraction f2) {
      Fraction[] fs = RCD(f1, f2);
      Fraction minus =  new Fraction(fs[0].numerator - fs[1].numerator,
        fs[0].denominator);
       return simpler(minus);
    }

     public  static Fraction multi(Fraction f1, Fraction f2) {
      Fraction multi =  new Fraction(f1.numerator * f2.numerator,
      f1.denominator * f2.denominator);
       return simpler(multi);
    }

     public  static Fraction div(Fraction f1, Fraction f2) {
       return multi(f1,  new Fraction(f2.denominator, f2.numerator));
    }

     public  static  void input(String s) {
      String[] ss = s.split( " ");
       if (ss.length == 1) {
        Fraction f = StringToFraction(ss[0]);
         if (f ==  null)
          output( "Usage: Should input a numeric");
         else
          output(f);
      }  else  if (ss.length == 3) {
        Fraction f1 = StringToFraction(ss[0]);
        Fraction f2 = StringToFraction(ss[2]);
         if (f1 ==  null) {
          output( "Usage: The first input should be numeric/numeric");
           return;
        }
         if (f2 ==  null) {
          output( "Usage: The third input should be numeric/numeric");
           return;
        }
         switch (ss[1].charAt(0)) {
         case '+':
          output(add(f1, f2));
           break;
         case '-':
          output(minus(f1, f2));
           break;
         case '*':
          output(multi(f1, f2));
           break;
         case '/':
          output(div(f1, f2));
           break;
         default:
          output( "Usage: The second input should be one of +-*/");
           break;
        }
      }  else
      output( "Usage: Should input one fraction or two fractions and a operator with the style 'f1 + f2'");
    }

     public  static  void output(Fraction f) {
       if (f.denominator == 1) {
        System.out.println(f.numerator);
         return;
      }
      StringBuilder sb =  new StringBuilder();
      sb.append(f.numerator);
      sb.append('/');
      sb.append(f.denominator);
      System.out.println(sb.toString());
    }

     public  static  void output(String s) {
      System.out.println(s);
    }

     private  static Fraction StringToFraction(String s) {
      String[] ss = s.split( "/");
       try {
         if (ss.length == 2)
           return simpler( new Fraction(Integer.valueOf(ss[0]), Integer
            .valueOf(ss[1])));
         else  if (ss.length == 1)
           return  new Fraction(Integer.valueOf(ss[0]));
         else
           return  null;
      }  catch (NumberFormatException e) {
          output( "Usage: Should input one fraction or two fractions and a operator with the style 'f1 + f2'");
      }
       return  null;
    }

  /**
  * both the numerator and denominator are divided by GCD
  */
     private  static Fraction simpler(Fraction f) {
       int gcd = GCD(f.numerator, f.denominator);
       if (gcd > 1)
         return  new Fraction(f.numerator / gcd, f.denominator / gcd);
       else
         return f;
    }

  /**
  * reduction to common denominator
  */
     private  static Fraction[] RCD(Fraction f1, Fraction f2) {
       int lcm = LCM(f1.denominator, f2.denominator);
       int m = lcm / f1.denominator;
       if (m > 1)
        f1 =  new Fraction(f1.numerator * m, f1.denominator * m);
      m = lcm / f2.denominator;
       if (m > 1)
        f2 =  new Fraction(f2.numerator * m, f2.denominator * m);
       return  new Fraction[] { f1, f2 };
    }

  /**
  * greatest common divisor
  */
     private  static  int GCD( int s,  int b) {
       // s-small,b-big
       if (s > b) {
         int temp = s;
        s = b;
        b = temp;
      }
       while (b != 0) {
         int temp = s % b;
        s = b;
        b = temp;
      }
       return s;
    }

  /**
  * a lowest common multiple
  */
     private  static  int LCM( int a,  int b) {
       return a * b / GCD(a, b);
    }

     public  static  void main(String[] args)  throws IOException {
       int c;
      StringBuilder sb =  new StringBuilder();
       while ((c = System.in.read()) != '\n')
        sb.append(( char) c);
      input(sb.toString());
      }
}