Java 有理数类 分数类 Rational类的设计与实现

要实现Rational类的加减乘除，要实现其可比较性，要覆盖toString()方法，要实现不同数据类型的转换等。

 package chapter14;

 public class Rational extends Number implements Comparable {
     private long numerator=0;
     private long denominator=1;

     public Rational(){
         this(0,1);
     }
     public Rational(long numerator, long denominator) {
         // TODO Auto-generated constructor stub
         long gcd=gcd(numerator,denominator);
         this.numerator=((denominator>0)?1:-1)*numerator/gcd;
         this.denominator=Math.abs(denominator)/gcd;
     }

     private static long gcd(long n, long d) {
         // TODO Auto-generated method stub
         long n1=Math.abs(n);
         long n2=Math.abs(d);
         int gcd=1;

         for(int k=1;k<=n1&&k<=n2;k++){
             if(n1%k==0&&n2%k==0)
                 gcd=k;
         }
         return gcd;
     }

     public long getNumerator(){
         return numerator;
     }
     public long getDenominator(){
         return denominator;
     }

     public Rational add(Rational secondRational){
         long n=numerator*secondRational.getDenominator()+
                 denominator*secondRational.getNumerator();
         long d=denominator*secondRational.getDenominator();
         return new Rational(n,d);
     }

     public Rational subtract(Rational secondRational){
         long n=numerator*secondRational.getDenominator()-
                 denominator*secondRational.getNumerator();
         long d=denominator*secondRational.getDenominator();
         return new Rational(n,d);
     }

     public Rational multiply(Rational sR){
         long n=numerator*sR.getNumerator();
         long d=denominator*sR.getDenominator();
         return new Rational(n,d);
     }

     public Rational divide(Rational sR){
         long n=numerator*sR.denominator;
         long d=denominator*sR.numerator;
         return new Rational(n,d);
     }

     public String toString(){
         if(denominator==1)
             return numerator+"";
         else
             return numerator+"/"+denominator;
     }

     public boolean equals(Object parm1){
         if((this.subtract((Rational)(parm1))).getNumerator()==0)
             return true;
         else
             return false;
     }

     @Override
     public int compareTo(Object o) {
         // TODO Auto-generated method stub
         if((this.subtract((Rational)o)).getNumerator()>0)
                 return 1;
         else if((this.subtract((Rational)o)).getNumerator()<0)
             return -1;
         else
             return 0;
     }

     @Override
     public int intValue() {
         // TODO Auto-generated method stub
         return (int)doubleValue();
     }

     @Override
     public long longValue() {
         // TODO Auto-generated method stub
         return (long)doubleValue();
     }

     @Override
     public float floatValue() {
         // TODO Auto-generated method stub
         return (float)doubleValue();
     }

     @Override
     public double doubleValue() {
         // TODO Auto-generated method stub
         return numerator*1.0/denominator;
     }

 }

　　有理数封装在Rational对象中。在机器内部，有理数总表示为它的最简形式，分子决定有理数的符号，分母总为正数。

　　gcd()方法是私有静态的。

　　Object类中的toString方法和equals方法在Rational类中被覆盖。toString（）方法以numerator/denominator的形式返回一个Rational对象的字符串表示。