关于Java中的多个构造函数

时间:2014-11-26 02:31:05

标签: java constructor

我对Java中的构造函数的多个实例有疑问。

我的任务是接收两个分数,然后乘以并除以这些分数。

我不确定如何为类对象本身的实例设置单独的值。

以下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?
    }
}

如果在上下文中难以理解,这里是我给出的完整起始代码:

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)
    {

    }
}

4 个答案:

答案 0 :(得分:5)

致电时:

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

在程序的main方法中,您将创建两个Rational类实例,一个名为r1,另一个名为r2。因为要将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代码实际上没有意义 - 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;    
}

将值n和d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类的私有部分中声明,并且实际上“属于”正在创建的实例然后将初始化为n和d的值。

Rational类体内的任何地方都应该引用成员变量firstNumfirstDen,而不是那些不属于类实例的变量。

答案 1 :(得分:1)

我假设Rational类应该代表一个有理数。你说:

//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?

不需要Rational类中存储两个分子和两个分母。您只需要创建两个Rational个对象。一个用于存储num1den1,另一个用于存储num2den2。你已经这样做了:

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

Rational中存储两个分子和两个分母是没有意义的。有理数只有一个。

总结:r1存储num1den1,而r2存储其他两个。当您创建新的Rational时,nd会引用您正在创建的特定实例的分子和分母。

答案 2 :(得分:1)

我不确定您的Rational实现是否符合您的意图,但构造函数不仅限于本地变量,它可以访问其可以访问的其他类中的任何静态变量。

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

nd是局部变量,num1den1是类TextLab05中的静态变量。

因此,您要使用来自另一个类的静态值分配局部变量。

代码没有意义,因为在将值分配给方法结束时处置的局部变量后,您不会对值执行任何操作。

答案 3 :(得分:0)

最重要的是要理解这个概念。您将在Rational班级中存储有理数。当你这样做时:

Rational r1 = new Rational(num1,den1);

您正在创建Rational的单个实例并将其命名为r1。 r1现在应该包含分子和分母(在这种情况下为num1den1)。

假设您要将数字设为一半,或1/2。你可以这样做:

Rational oneHalf = new Rational(1,2);

意识到new Rational(1,2)正在调用Rational类的构造函数。在构造函数中,您需要将numden分配给传递的值(在本例中为1和2)。所以你需要这样的东西:

this.num = num1;
this.den = den1;

因此,如果您希望能够将一个Rational与另一个Rational相乘,则需要一个方法或函数来执行此操作。在Rational课程中,创建一个名为multiply(Rational anotherRational)的方法。

该功能将执行以下操作:

this.num = this.num * anotherRational.num;
this.den = this.den * anotherRational.den;

我放弃了一半答案,我会让你做其余的事。不要只是复制你在这里找到的东西,想想你正在做什么。