Question

我正在编写一个编码分配，我应该编写方法来简化，找到gcf，加，减，乘和除以两个分数。我已经编写了所有方法，但是我在divide方法中遇到了麻烦，因为每当我尝试除以负分数（例如-6/17）时，它就会打印0/1作为结果。这是我的Fraction类，包含所有方法，但我添加的只有上面列出的那些。其余的由我的导师提供。这是班级：

class Fraction {
    private int numerator = 0; // numerator (and keeps sign)
    private int denominator = 1; // always stores positive value

    public Fraction() {
    }

    public Fraction(int n, int d) {
        if (set(n, d) == false)
           set(0, 1);
    }

    public boolean set(int n, int d) {
        if (d > 0) {
           numerator = n;
           denominator = d;
           return true;
        } else
           return false;
    }

    public String toString() {
       return (numerator + "/" + denominator);
    }

    public int getNumerator() {
        return numerator;
    }

    public int getDenominator() {
        return denominator;
    }

    public double decimal() {
        return (double) numerator / denominator;
    }

    public Fraction simplify(){
       int gcd = GetGcd(this);

       int simpNum = this.numerator;
       int simpDen = this.denominator;

       simpNum /= gcd;
       simpDen /= gcd;

       Fraction f = new Fraction (simpNum, simpDen);
       return f;
    }

    public int GetGcd (Fraction f){
       int testNum = f.numerator;
       int testDen = f.denominator;

       if (testNum < 0)
           testNum = 0 - testNum;
       else if (testDen < 0)
           testDen = 0 - testDen;

       if (testNum == 0){
           return testDen;
       }

       while (testNum != testDen){
           if (testNum > testDen)
              testNum -= testDen;
           else
              testDen -= testNum;

       }
      return testNum;
    }

    public Fraction add (Fraction f){
       int cd = this.denominator * f.denominator;

       int den1 = this.denominator;
       int den2 = f.denominator;
       int num1 = this.numerator * (cd / den1);
       int num2 = f.numerator * (cd / den2);
       int num3 = num1 + num2;
       Fraction f2 = new Fraction (num3, cd);
       f2 = f2.simplify();
       return f2;
    }

    public Fraction subtract (Fraction f){
       int cd = this.denominator * f.denominator;

       int den1 = this.denominator;
       int den2 = f.denominator;
       int num1 = this.numerator * (cd / den1);
       int num2 = f.numerator * (cd / den2);
       int num3 = num1 - num2;

       Fraction f2 = new Fraction (num3, cd);
       f2 = f2.simplify();
       return f2;
    }

    public Fraction multiply (Fraction f){
       int den1 = this.denominator;
       int den2 = f.denominator;
       int num1 = this.numerator;
       int num2 = f.numerator;
       int num3 = num1 * num2;
       int den3 = den1 * den2;

       Fraction f2 = new Fraction (num3, den3);
       f2 = f2.simplify();
       return f2;
    }

    public Fraction divide (Fraction f){
       int den1 = this.denominator;
       int den2 = f.denominator;
       int num1 = this.numerator;
       int num2 = f.numerator;

       int num3 = num1 * den2;
       int den3 = den1 * num2;

       Fraction f2 = new Fraction (num3, den3);
       f2 = f2.simplify();
       return f2;
    }
}

我的教练给了我一个测试代码的测试代码。这是：

    public class FractionTester {
    public static void main (String[] args) {

    System.out.println("\n\nFraction tests:\n");

    Fraction f1 = new Fraction(4, 6);
    Fraction f2 = new Fraction(75, 175);
    Fraction f3 = new Fraction(-6, 17);

    System.out.println(f1 + " simplified = " + f1.simplify());
    System.out.println(f2 + " simplified = " + f2.simplify());
    System.out.println(f3 + " simplified = " + f3.simplify());

    // show that f1, f2, f3 haven't changed
    System.out.println("f1 = " + f1);
    System.out.println("f2 = " + f2);
    System.out.println("f3 = " + f3);

    // arithmetic
    System.out.println(f1 + " + " + f2 + " = " + f1.add(f2));
    System.out.println(f1 + " - " + f2 + " = " + f1.subtract(f2));
    System.out.println(f1 + " * " + f2 + " = " + f1.multiply(f2));
    System.out.println(f1 + " / " + f2 + " = " + f1.divide(f2));
    System.out.println();

    System.out.println(f2 + " + " + f3 + " = " + f2.add(f3));
    System.out.println(f2 + " - " + f3 + " = " + f2.subtract(f3));
    System.out.println(f2 + " * " + f3 + " = " + f2.multiply(f3));
    System.out.println(f2 + " / " + f3 + " = " + f2.divide(f3));
    System.out.println();

    // test 'division by zero' handling
    Fraction zero = new Fraction();
    System.out.println(f2 + " / " + zero + " = " + f2.divide(zero));
  }
}

结果应该显示如下：

4/6 simplified = 2/3
75/175 simplified = 3/7
-6/17 simplified = -6/17
f1 = 4/6
f2 = 75/175
f3 = -6/17
4/6 + 75/175 = 23/21
4/6 - 75/175 = 5/21
4/6 * 75/175 = 2/7
4/6 / 75/175 = 14/9

75/175 + -6/17 = 9/119
75/175 - -6/17 = 93/119
75/175 * -6/17 = -18/119
75/175 / -6/17 = -17/14 (THIS SHOWS UP AS 0/1 INSTEAD...)

75/175 / 0/1 = 0/1

我知道它在Divide方法中的一些东西，因为当我在最后一个方法中将-6/17改为6/17时，它在简化后工作并打印17/14。我只是不知道Divide方法中的哪些方法不适用于负分数。我可以添加一些东西来帮助解决这个问题吗？提前谢谢。

Answer 1

在divide()，

public Fraction divide (Fraction f){
   int den1 = this.denominator;
   int den2 = f.denominator;
   int num1 = this.numerator;
   int num2 = f.numerator;

   int num3 = num1 * den2;
   int den3 = den1 * num2;

   Fraction f2 = new Fraction (num3, den3);
   ...

假设this为正，而f为否定。根据你的假设，

den1 > 0
den2 > 0
num1 > 0
num2 < 0
num3 = num1 * den2 > 0
den3 = den1 * num2 < 0

但是，当new Fraction(num3, den3)调用set()时，

public boolean set(int n, int d) {
    if (d > 0) {
       numerator = n;
       denominator = d;
       return true;
    } else
       return false;
}

当分母小于0时，您返回false，禁止将值设置到类中。

您可以反转分子和分母的符号，而不是简单地返回false。

Answer 2

尝试将set方法更改为：

public boolean set(int n, int d) {
    if (d > 0) {
       numerator = n;
       denominator = d;
       return true;
    } 
    else if (d < 0) {
        numerator = n * -1;
        denominator = d * -1;
        return true;
    }
    else
       return false;
}

如果没有第二个if语句，set将对具有负恶魔的分数评估为false。在这种情况下，Fraction方法返回的divide将为0/1。

否定分数划分的问题

2 个答案: