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。