Thread: User Defined Decimal Precision

Return a String representation of a Rational number in floating-point format. (Consider providing formatting capabilities that enable the user of the class to specify the number of digits of precision to the right of the decimal point.)

I am trying to take a user defined floating-point formatted number from a rational number that is also user defined and put through arithmetic methods. Currently my issue is where to input the prompt for the user to input the value for the floating-point variable and allowing it to be put through the correct method which I defined as toFloat to format the rational number.

 
public String toFloat() {
        float num;
        int n;
        Scanner input = new Scanner(System.in);
        System.out.print("Enter precision: ");
        n = input.nextInt();
        float numerator = this.getNumerator();
        float denominator = this.getDenominator();
        num = numerator / denominator;
        DecimalFormat df = new DecimalFormat();
        df.setMaximumFractionDigits(n);
        return df.format(num);
    }

Currently I have it inside the toFloat method but the output example provided to me shows the scanner for precision being called when inputting the values for the rational number.

public Rational inputR() {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter numerator: ");
        numerator = input.nextInt();
        System.out.print("Enter denominator: ");
        denominator = input.nextInt();
        return new Rational(numerator, denominator);
        }

The constructor Rational is defined as numerator and denominator but not precision as if I do this it prompts me to input precision twice which I do not want. My question is how could I implement the scanner for toFloat outside of the method to be called before and still applied to toFloat.

I would like to use the same scanner from inputR to get the variable n that would be used in toFloat rather than having a separate scanner in that method. As for the output example I am not sure how to post it here as the manage attachments is not opening. However it "should" look similar to :

Enter numerator: 2
Enter denominator: 4
Enter numerator: 3
Enter denominator: 9
Enter precision: 2
1. ADD
2. SUBTRACT
3. MULTIPLY
4. DIVIDE
5. EXIT
Enter your choice:

I am getting it to display as:

Enter numerator: 2
Enter denominator: 4
Enter numerator: 3
Enter denominator: 9
1. ADD
2. SUBTRACT
3. MULTIPLY
4. DIVIDE
5. EXIT
Enter your choice: 3
Enter precision: 2

And then my output from the arithmetic methods.

Originally Posted by Norm

Sorry, I do not see what the difference is between: it "should" look similar to : and I am getting
Can you add some comments in the output that says what is wrong? For example: <<< This should be 4 not 9

Enter numerator: 2
Enter denominator: 4
Enter numerator: 3
Enter denominator: 9
Enter precision: 2 <<<<<< I need precision here
1. ADD
2. SUBTRACT
3. MULTIPLY
4. DIVIDE
5. EXIT
Enter your choice:

But I am getting the precision prompt after I select the arithmetic method to be called.

Enter numerator: 2
Enter denominator: 4
Enter numerator: 3
Enter denominator: 9
1. ADD
2. SUBTRACT
3. MULTIPLY
4. DIVIDE
5. EXIT
Enter your choice: 3
Enter precision: 2 <<<<<<< I want this to be called before I choose add, subtract, multiply, divide, or exit.


If you want to use the same Scanner instance declared in the inputR method in the toFloat method, its reference can be passed as an argument to the toFloat method.

How would I go about passing a scanner as an argument. Currently I have two different scanners as when I try to use the scanner from inputR it prompts me to input the precision value twice. I have all the functions working correctly with each other and the precision works when called later in my output. What I am trying to do is input the value of that variable n for precision in toFloat before I chose the arithmetic function.

Originally Posted by Norm

The same way you pass any argument to a method and receive it in the method

Type refToType = new Type();  // define an instance the Type class
...
someMethod(refToType);    //  pass reference to someMethod
...
private void someMethod(Type aType) {   // receive reference to the Type object
   // here the code can use the Type object
}

Hard to say why the methods are called in the order that create the shown output. Can you post the code?

 
import java.text.DecimalFormat;
import java.util.Scanner;
 
class Rational {
 
    private int numerator;
    private int denominator;
 
    //constructors
    Rational() {
        numerator = 0;
        denominator = 1;
    }
 
    Rational(int num, int den) {
        numerator = num;
        denominator = den;
    }
 
    //getters
    public int getNumerator() {
        return numerator;
    }
 
    public int getDenominator() {
        return denominator;
    }
 
    //modifiers
    public void setNumerator(int num) {
        numerator = num;
    }
 
    public void setDenominator(int den) {
        denominator = den;
    }
 
    //Take input for rational number
    public Rational inputR() {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter numerator: ");
        numerator = input.nextInt();
        System.out.print("Enter denominator: ");
        denominator = input.nextInt();
        return new Rational(numerator, denominator);
        }
 
        public int precision() {
            int n;
            Scanner input = new Scanner(System.in);
            System.out.print("Enter precision: ");
            n = input.nextInt();
            return n;
        }
 
    // Find the GCD
 
    //Add 2 rational numbers
    public Rational add(Rational x) {
        int n;
        int d;
        n = (numerator * x.denominator) + (x.numerator * denominator);
        d = denominator * x.denominator;
        return new Rational(n, d);
    }
 
    //Subtract 2 rational numbers
    public Rational subtract(Rational x) {
        int n;
        int d;
        n = (numerator * x.denominator) - (x.numerator * denominator);
        d = denominator * x.denominator;
        return new Rational(n, d);
    }
 
 
    //multiply 2 rational numbers
    public Rational multiply(Rational x) {
        int n;
        int d;
        n = numerator * x.numerator;
        d = denominator * x.denominator;
        return new Rational(n, d);
    }
 
    public Rational divide(Rational x) {
        return new Rational(numerator * x.denominator, denominator * x.numerator);
    }
 
    public String toFloat() {
        float num;
        int n = precision();
        float numerator = this.getNumerator();
        float denominator = this.getDenominator();
        num = numerator / denominator;
        DecimalFormat df = new DecimalFormat();
        df.setMaximumFractionDigits(n);
        return df.format(num);
    }
 
    //Print rational number to string
    public String toString() {
        return numerator + "/" + denominator;
    }
 
}
 
public class testRational {
 
 
    public static void main(String[] args) {
 
        Rational x1 = new Rational();
        Rational x2 = new Rational();
        Rational x3;
        x1.inputR();
        x2.inputR();
 
        Scanner input = new Scanner(System.in);
 
    while (true) {
 
 
        System.out.println("1. ADD");
        System.out.println("2. SUBTRACT");
        System.out.println("3. MULTIPLY");
        System.out.println("4. DIVIDE");
        System.out.println("5. EXIT");
        System.out.print("Enter your choice: ");
 
 
        int choice;
 
 
        choice = input.nextInt();
 
        if (choice > 5) {
            System.out.println("Invalid Choice");
        }
 
        switch (choice) {
 
            case 1:
                x3 = x1.add(x2);
                System.out.println("a + b = " + x3 + " = " + x3.toFloat());
                break;
 
            case 2:
                x3 = x1.subtract(x2);
                System.out.println("a - b = " + x3 + " = " + x3.toFloat());
                break;
 
            case 3:
                x3 = x1.multiply(x2);
                System.out.println("a * b = " + x3 + " = " + x3.toFloat());
                break;
 
            case 4:
                x3 = x1.divide(x2);
                System.out.println("a / b = " + x3 + " = " + x3.toFloat());
                break;
 
            case 5:
                System.exit(0);
            }
        }
    }
}

This is what I currently have with everything working except where the prompt is being brought up to format.

Originally Posted by Norm

Can you make a list of the steps you want the code to take to show what order you want the methods called?

The precision is being called during my switch statements as that is where the value that needs to be formatted is being output. I need precision to be called before toFormat occurs. The variable n needs to be applied to toFloat from precision.

List:

1. inputR to get 2 numerators and 2 denominators
2. precision to get variable n that is applied to toFloat
3. User inputs what arithmetic method they want to execute
4. toFloat
5. output statement containing the fraction from the arithmetic function and number with decimal format