Question

我正在尝试编写这个java程序，供用户输入两个有理数，并从选项菜单中询问计算某种功能A.我被困在几个地方，不知道还有什么去做。我需要一些指导。它不会编译。说构造函数Rational是未定义的，最后一个默认是无效标签.it是驱动程序文件使用有理文件的两个类文件。这两个文件都是按文本上传和分隔的。需要帮助

 import java.util.Scanner;
 import java.util.*; 

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

 int rationalNum1, rationalDen1, rationalNum2, rationalDen2;

 Scanner in = new Scanner(System.in); 
 // first rational 
 System.out.println(" Input first rational number for the Numerator");
 rationalNum1 = in.nextInt();
 System.out.println(" Input first rational number for the Denominator");
 rationalDen1 = in.nextInt();
 if (rationalDen1 == 0){
 System.out.println(" Cannont divide by zero ");
 System.out.println(" please re enter another number ");
 }
 System.out.println("Rational Number #1 = ("+rationalNum1+"/"+rationalDen1+")");          
//Displays 1st Rational Number

// second rational
System.out.println(" Input 2nd rational number for the 2nd Numerator");
rationalNum2 = in.nextInt();
System.out.println(" Input 2nd rational number for the 2nd Denominator");
rationalDen2 = in.nextInt();
if (rationalDen2 == 0){
System.out.println("Cannont divide by zero");
System.out.println(" please re enter another number");
}
System.out.println("Rational Number #2 = ("+rationalNum2+"/"+rationalDen2+")");  
 //Displays 2nd Rational Number

 Rational r1 = new Rational ( rationalNum1, rationalDen1);
 Rational r2 = new Rational ( rationalNum2, rationalDen2);

     // System.out.println;//toString
   }


 public void display_menu() //menu options 
 {
 System.out.print(" Enter the corresponding number for the desired action ");
 System.out.println("1) Addition\n2) 2) Subtraction\n3) 3) Multiplication\n4)    4)Division\n5) 5) Test for Eqaulity\n6) 6) Change 1st rational number\n7) 7) Change 2nd rational number"); 
}    
public void question()
{
 System.out.println("Do you want to exit? [y/n]");  // ask user if they want to quit   with yes or no option
Scanner q = new Scanner(System.in);
switch (q.nextInt()) 
 {
 case 'y' :
 System.out.println ("Thank you and goodbye.");
 break;

 case 'n' :
 InputMenu();
 break;
 default:

 System.err.println ( "Unrecognized option" );
 break;
 }
}
public void InputMenu()  // keys for the menu
{
Scanner in = new Scanner(System.in);
display_menu();
switch (in.nextInt()) 
{
 case 1: //addition
 System.out.println ( "1" );
 System.out.println( "("+rationalNum1+"/"+rationalDen1+")"+ " + " + " ("+rationalNum2+"/"+rationalDen2+")" + "=" +  r1.add(r2));   
 break;

 case 2: //subtraction
 System.out.println ( "2" );
 System.out.println( "("+rationalNum1+"/"+rationalDen1+")"+ " - " + "("+rationalNum2+"/"+rationalDen2+")" + "=" +  r1.subtract(r2));   
 break;

 case 3: //mulitplication 
 System.out.println ( "3" );
 System.out.println( "("+rationalNum1+"/"+rationalDen1+")"+ " * " + "      ("+rationalNum2+"/"+rationalDen2+")" + "=" +  r1.multiply(r2));    
 break;

 case 4: //division
 System.out.println ( "4" );
 System.out.println( "("+rationalNum1+"/"+rationalDen1+")"+ " / " + "("+rationalNum2+"/"+rationalDen2+")" + "=" +  r1.divide(r2));      
 break;

 case 5: //compare to
 System.out.println ( "5" );
 question();
 break;

 case 6: //change the 1st Rational Number
 System.out.println ( "6" );
 Scanner in = new Scanner(System.in); 
 System.out.println(" Input first rational number for the Numerator");
 rationalNum1 = in.nextInt();
 System.out.println(" Input first rational number for the Denominator");
 rationalDen1 = in.nextInt();
 if (rationalDen1 == 0){
 System.out.println(" Cannont divide by zero");
 System.out.println(" please re enter another number");
 }
 break;

 case 7: //change the 2nd Rational Number
 System.out.println ( "7" );
 System.out.println(" Input 2nd rational number for the 2nd Numerator");
 rationalNum2 = in.nextInt();
 System.out.println(" Input 2nd rational number for the 2nd Denominator");
 rationalDen2 = in.nextInt();
 if (rationalDen2 == 0){
 System.out.println("Cannont divide by zero");
 System.out.println(" please re enter another number");
 break;


 default:
 System.err.println ( "Unrecognized option" );
 break;
}
}
}
}

这是理性

的类文件

public class Rational{

 private int Numerator;
 private int Denominator;


 //constructors
 public Rational(){  
 Numerator = 1;
 Denominator = 1 ;

 }

//setters 
//a-numerator
//b-denmonator 
 //c other.getNumerator
 //d-other.getDenominator
   public void add (Rational other){                    // (ad + bc) / bd                          
   Numerator = (Numerator*other.getDenominator() + Denominator*other.getNumerator());
   Denominator = (Denominator*other.getDenominator());
  //Normalize();
   }
   public void subtract (Rational other){               // (ad-bc) / bd
   Numerator = (Numerator*other.getDenominator() - Denominator*other.getNumerator());
   Denominator = (Denominator*other.getDenominator());
   //Normalize();
   } 
  public void multiply (Rational other){                   // ac/db
  Numerator = (Numerator*other.getNumerator() / other.getDenominator()* Denominator);
  // Normalize();
  }
 public void divide (Rational other){// 
 }

  public int getNumerator(){
  return Numerator;
  }

  public int getDenominator(){
  return Denominator;
  }

 //toString    
 //public String toString(){
 //return toString()+ (rationalNum1 + "/" +  rationalDen1);
 }

Answer 1

在你的主要课程中你有：

Rational r1 = new Rational ( rationalNum1, rationalDen1);
Rational r2 = new Rational ( rationalNum2, rationalDen2);

你将2个整数传递给一个返回void的构造函数，所以你必须改变你的构造函数（Rational类），如下所示：

 public Rational(int rationalNumber, int rationalDen){  
 Numerator = rationalNumber;
 Denominator = rationalDen;

 }

希望它有所帮助，让我知道它是否有效或是否有更多错误......

编辑：您的扫描仪和打印错误。你有这个：

public void question()
{
 System.out.println("Do you want to exit? [y/n]");  // ask user if they want to quit   with yes or no option
 Scanner q = new Scanner(System.in);
 switch (q.nextInt()) // here you are assuming that you are reading a int in step 
 {                    // of a string
 case 'y' : // ' ' arent used for strings...
 System.out.println ("Thank you and goodbye.");
 break;

 case 'n' :
 InputMenu();
 break;
 default:

 System.err.println ( "Unrecognized option" );
 break;
 }
}

所以，你需要的是：

 public void question()
{
 System.out.println("Do you want to exit? [y/n]");  // ask user if they want to quit   with yes or no option
 Scanner q = new Scanner(System.in);
 switch (q.nextLine()) // change nextInt to nextLine, that is the string method 
 {                    // of a string
 case "y" : //change ' ' to " "
 System.out.println ("Thank you and goodbye.");
 break;

 case "n" :  //change ' ' to " "
 InputMenu();
 break;
 default:

 System.err.println ( "Unrecognized option" );
 break;
 }
}

希望有所帮助：）

编辑3：

你的代码中有

：` 公共类RationalDriver { public static void main（String [] args）{

 int rationalNum1, rationalDen1, rationalNum2, rationalDen2; // this are local variables, they only exist inside main method
...`
}

所以，你能做的是：

 public class RationalDriver{
 private static int rationalNum1, rationalDen1, rationalNum2, rationalDen2;
 public static void main(String[] args){
  // your main
 }

我所做的是在你的主要文件中使用仅存在的局部变量，并将它们转换为全局变量，这样当你想要改变它们的值或给它们一个值时你就可以了：

rationalNum1 = your valor;

请注意，如果您使用任何变量而不使用值初始化它，您将获得零点异常...

Answer 2

您需要创建一个构造函数Rational (int rationalNum1, int rationalDen1){}

在你的程序中，你使用了构造函数Rational ( rationalNum1, rationalDen1) 当你只声明默认构造函数public Rational()时，它不接受任何参数。

可以为一个类提供多个构造函数，并根据它们接受的参数的类型和数量来区分它们。

E.g

class A(int a, int b);

与

相同

Class A(int c, int b);

但不是

Class(int a, float d)

需要帮助编译此迭代和接口程序

2 个答案: