java - 关于 Java 中的多个构造函数

Question

我对 Java 中构造函数的多个实例有疑问。

我的任务是接收两个分数，然后对这些分数进行乘除。

我不确定如何为类对象本身的实例设置单独的值。

这是我遇到问题的示例代码:

import java.util.Scanner;

public class TextLab05
{
    static int num1, den1;   // numerator and denominator of the 1st rational number
    static int num2, den2;   // numerator and denominator of the 2nd rational number

    public static void main (String args[])
    {
        enterData();

        Rational r1 = new Rational(num1,den1);
        Rational r2 = new Rational(num2,den2);
    }
}

class Rational
{

    private int firstNum;   // entered numerator
    private int firstDen;   // entered denominator
    private int num;        // reduced numerator
    private int den;        // reduced denominator

    public Rational()
    {

    }

    public Rational(int n, int d)
    {
        n = TextLab05.num1;
        d = TextLab05.den1;
        //Here specifically is where I am having comprehension issues. How can I include num2 and den2 if I only have int n and int d?
    }
}

如果脱离上下文很难理解，这里是我得到的完整起始代码:

import java.util.Scanner;

public class TextLab05
{
    static int num1, den1;   // numerator and denominator of the 1st rational number
    static int num2, den2;   // numerator and denominator of the 2nd rational number

    public static void main (String args[])
    {
        enterData();

        Rational r1 = new Rational(num1,den1);
        Rational r2 = new Rational(num2,den2);
        Rational r3 = new Rational();

        r3.multiply(r1,r2);
        System.out.println("\n\n" + r1.getOriginal() + " * " + r2.getOriginal() + "  =  " + r3.getRational());
        r3.divide(r1,r2);
        System.out.println("\n" + r1.getOriginal() + " / " + r2.getOriginal() + "  =  " + r3.getRational());

        //      100 Point Version Only
        //      r3.add(r1,r2);
        //      System.out.println("\n" + r1.getOriginal() + " + " + r2.getOriginal() + "  =  " + r3.getRational());
        //      r3.subtract(r1,r2);
        //      System.out.println("\n" + r1.getOriginal() + " - " + r2.getOriginal() + "  =  " + r3.getRational());
        System.out.println();
    }

    public static void enterData()
    {
        Scanner input = new Scanner(System.in);
        System.out.print("\nEnter the 1st numerator ----> ");
        num1 = input.nextInt();
        System.out.print("\nEnter the 1st denominator --> ");
        den1 = input.nextInt();
        System.out.print("\nEnter the 2nd numerator ----> ");
        num2 = input.nextInt();
        System.out.print("\nEnter the 2nd denominator --> ");
        den2 = input.nextInt();
    }
}

class Rational
{

    private int firstNum;   // entered numerator
    private int firstDen;   // entered denominator
    private int num;        // reduced numerator
    private int den;        // reduced denominator

    public Rational()
    {

    }

    public Rational(int n, int d)
    {
        n = TextLab05.num1;
        d = TextLab05.den1;
    }

    private int getGCF(int n1,int n2)
    {
        int rem = 0;
        int gcf = 0;
        do
        {
            rem = n1 % n2;
            if (rem == 0)
                gcf = n2;
            else
            {
                n1 = n2;
            n2 = rem;
            }
        }
        while (rem != 0);
        return gcf;
     }

    public int getNum()
    {
        return TextLab05.num1;
    }

    public int getDen()
    {
        return TextLab05.den1;
    }

    public double getDecimal()
    {
        return (double)TextLab05.num1 / TextLab05.den1;
    }

    public String getRational()
    {
        String rational = "" + TextLab05.num1 + "/" + TextLab05.den1;
        return rational;
    }

    public String getOriginal()
    {
        String original = "" + TextLab05.num1 + "/" + TextLab05.den1;
        return original;
    }

    public void reduce()
    {

    }
    public void multiply(Rational r1, Rational r2)
    {

    }
    public void divide(Rational r1, Rational r2)
    {

    }
    public void add(Rational r1, Rational r2)
    {

    }
    public void subtract(Rational r1, Rational r2)
    {

    }
}

Answer 1

当你打电话时:

Rational r1 = new Rational(num1, den1);
Rational r2 = new Rational(num2, den2);

在程序的主要方法中，您正在创建 Rational 类的两个实例，一个名为 r1，一个名为 r2。因为您将 int 值传递给 Rational 构造函数，所以将调用的构造函数是需要两个整数参数的构造函数:

public Rational(int n, int d)
{
    ...
} 

编译器知道这一点，因为它匹配构造函数的名称​​以及传递的参数类型(称为匹配构造函数的“签名”)。

在您提供的代码中，Rational Constructor 代码没有任何意义 - 这段代码:

public Rational(int n, int d)
{
   n = TextLab05.num1;
   d = TextLab05.den1;    
}

应该看起来像这样:

public Rational(int n, int d)
{
   this.firstNum = n;
   this.firstDen = d;    
}

值 n 和 d 被传递给构造函数，然后在构造函数的主体中实例变量 firstNum 和 firstDen (它们在 Rational 类的私有(private)部分中声明并且有效地“属于”正在创建的实例) 然后将被初始化为 n 和 d 的值。

在 Rational 类主体中的任何地方，您都应该引用成员变量 firstNum 和 firstDen，而不是不“属于”类实例的变量。