public?class?Arithmetic?{
	private?int?a;
	private?int?b;
	private?int?c;
	private?int?d;
	//兩個有理數(shù)分別是a/b和c/d;
	public?Arithmetic(int?a,int?b,int?c,int?d){
		super();
		if(b==0||d==0)
			throw?new?RuntimeException("分母不能為零");
		this.a=a;
		this.b=b;
		this.c=c;
		this.d=d;
	}
	public?String?add(){
		int?remainder=greatestCommonDivisor(Math.abs(a*d+c*b),Math.abs(b*d));
		return??showAsFraction((a*d+c*b)/remainder,b*d/remainder);
	}	
	public?String?sub(){
		int?remainder=greatestCommonDivisor(Math.abs(a*d-c*b),Math.abs(b*d));
		return??showAsFraction((a*d-c*b)/remainder,b*d/remainder);
	}	
	public?String?multiply(){
		int?remainder=greatestCommonDivisor(Math.abs(a*c),Math.abs(b*d));
		return??showAsFraction(a*c/remainder,b*d/remainder);
	}
	public?String?divide(){
		int?remainder=greatestCommonDivisor(Math.abs(a*d),Math.abs(b*c));
		return??showAsFraction(a*d/remainder,b*c/remainder);
	}
	//求最大公約數(shù)
	public?int?greatestCommonDivisor(int?numerator?,int?denominator){
		int?bigger;
		int?smaller;
		if(numerator>denominator){
			?bigger=numerator;
			?smaller=denominator;
		}else{
			?bigger=denominator;
			?smaller=numerator;
		}
		int?remainder=bigger%smaller;
		while(remainder!=0){
			bigger=smaller;
			smaller=remainder;
			remainder=bigger%smaller;
		}
		return?smaller;
	}
	
	public?String?showAsFraction(int?numerator?,int?denominator){
		if((numerator>0&&denominator>0)||(numerator<0&&denominator<0))
			return?Math.abs(numerator)+"/"+Math.abs(denominator);
		else
			return?"-"+Math.abs(numerator)+"/"+Math.abs(denominator);
	}
}

純手打望采納！