面向对象Java与分数

Question

我试图将三个实例方法添加到类“Fraction”的公共接口中，结果都返回一个“Fraction”：

加、减、乘。是否可以将其从当前代码更改为实例方法

我就是不能让它工作

这是我的密码：

class Fraction {
    private Integer numerator;
    private Integer denumerator;

    public Fraction(Integer numerator, Integer denumerator) {

        int gcd = 1;

        for (int i = 1; i <= numerator && i <= denumerator; i++) {
            if (numerator % i == 0 && denumerator % i == 0)
                gcd = i;
        }
        this.numerator = numerator / gcd;
        this.denumerator = denumerator / gcd;
    }

    public Fraction(Integer numerator) {
        this.numerator = numerator;
        this.denumerator = 1;
    }

    public String toString() {

        return numerator + "/" + denumerator;
    }



    public static Fraction add(Fraction f1,Fraction f2){
        return new Fraction(f1.numerator*f2.denumerator+f2.numerator*f1.denumerator,f1.denumerator*f2.denumerator);
    }
    public static Fraction subtract(Fraction f1,Fraction f2){
        return new Fraction(f1.numerator*f2.denumerator-f2.numerator*f1.denumerator,f1.denumerator*f2.denumerator);
    }
    public static Fraction mul(Fraction f1,Fraction f2){
        return new Fraction(f1.numerator*f2.numerator,f1.denumerator*f2.denumerator);
    }
}

class Main
{
    public static void main(String[] arguments)
    {
        final Fraction HALF = new Fraction(1, 2);
        final Fraction THREE_FIFTH = new Fraction(3, 5);
        System.out.println(HALF.add(HALF, THREE_FIFTH).toString());
        System.out.println(THREE_FIFTH.subtract(HALF, THREE_FIFTH).toString());
        System.out.println(HALF.mul(HALF, THREE_FIFTH).toString());
    }
}

Answer 1

public static Fraction add(Fraction f1,Fraction f2){
  return new Fraction(f1.numerator*f2.denumerator+f2.numerator*f1.denumerator,
                      f1.denumerator*f2.denumerator);
}

是一个类方法（因为static，它不需要一个实例来调用“on”）

使其成为一个实例方法

public Fraction add(Fraction other){
  return new Fraction(this.numerator*other.denumerator+other.numerator*this.denumerator,
                      this.denumerator*other.denumerator);
}

当然，您实际上不需要在那里写this，只是它们强调f1成为当前对象，而f2成为单个参数

那你就可以把它当作

Fraction HALF = new Fraction(1, 2);
Fraction THREE_FIFTH = new Fraction(3, 5);
System.out.println(HALF.add(THREE_FIFTH));

不重复HALF（就像原始代码中的HALF.add(HALF,THREE_FIFTH)）

旁注：类方法（staticstuff）可以通过类的名称引用，您的原始代码将以Fraction.add(...)的形式进行更常规的调用：

System.out.println(Fraction.add(HALF,THREE_FIFTH));

（System.out.println()知道它应该调用toString()，所以实际上您不需要自己去做）