Convert String to Double?

Question

This is a two part code with a tester class. For some reason I can't figure out how to convert this string variable to code correctly involved in the equation gradeNum = grad - .3 and gradeNum = grade + 0.3. Any ideas?

/** This is my class Grade */
    public class Grade
{

    private String grade;
    private double gradeNum;


// Constructor
public Grade(String showGrade)
{
    grade = showGrade;
    gradeNum = 0;
}


// getNumericGrade method to return grade number
public double getNumericGrade()
{
    if (grade.equalsIgnoreCase("A") || grade.equalsIgnoreCase("A+"))
{
    gradeNum = 4.0;
}
    else if (grade.equalsIgnoreCase("A-"))
{
    gradeNum = 3.7;
}


    if (grade.equalsIgnoreCase("B"))
{
    gradeNum = 3.0;
}
    else if (grade.equalsIgnoreCase("B+"))
{
    gradeNum = 3.3;
}
    else if (grade.equalsIgnoreCase("B-"))
{
    gradeNum = 2.7;
}


    if (grade.equalsIgnoreCase("C"))
{
    gradeNum = 2.0;
}
    else if (grade.equalsIgnoreCase("C+"))
{
    gradeNum = 2.3;
}
    else if (grade.equalsIgnoreCase("C-"))
{
    gradeNum = 1.7;
}


    if (grade.equalsIgnoreCase("D"))
{
    gradeNum = 1.0;
}
    else if (grade.equalsIgnoreCase("D+"))
{
    gradeNum = 1.3;
}
    else if (grade.equalsIgnoreCase("D-"))
{
    gradeNum = .7;
}

    if (grade.equalsIgnoreCase("F"))
{
    gradeNum = 0.0;
}

    return gradeNum;


    System.out.println("Invalid letter grade");
    return -1.0;


}
}


/** This is my class tester
 */

import java. util .Scanner;

/**
This program tests the numeric grade with a given letter grade.
*/
public class GradeTester 
{
public static void main(String[] args)
{
    Scanner in = new Scanner(System.in);

    System.out.println("Enter a letter grade: ");
    String showGrade = in.nextLine();

    Grade gg = new Grade(showGrade);

    System.out.print("Numeric Value: ");
    System.out.println(gg.getNumericGrade());

    in.close();

}
}

Keale, have you looked at his question? They're not trying to parse doubles from strings, they're trying to catch GPA's as letters and return the appropriate double. — Neverwork2123
– Neverwork2123, Commented Nov 5, 2014 at 1:56
equalsIgnoreCase compares an entire string. If the input is "B+", there will not be any place in your code that sets gradeNum to 3.0. You will want to use one or more of these methods in the String class: length(), charAt(), substring(). — ajb
– ajb, Commented Nov 5, 2014 at 1:59
Sorry I'm a beginner at Java. Seems that all these options are wanting me to add in the tester class. Is that where I put it? — Courtney
– Courtney, Commented Nov 5, 2014 at 2:03
@Courtney You would use these in getNumericGrade, because they will help getNumericGrade return the correct result. — ajb
– ajb, Commented Nov 5, 2014 at 2:11

Ken Y-N · Accepted Answer · 2014-11-05 02:01:39Z

1

Instead of if (grade.equalsIgnoreCase("B")) etc, use:

if (Character.toUpperCase(grade.charAt(0)) == 'B')

And instead of grade.equalsIgnoreCase("A-") etc, use:

if (grade.length() > 1 && grade.charAt(1) == '-')

This should be enough to enable you to fix your problem.

NOTE: There are other changes that need to be made, but I don't want to just spoon-feed you the correct code.

answered Nov 5, 2014 at 2:01

Ken Y-N

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3 Comments

ajb Over a year ago

@DavidWallace How would it "not make a difference"? If the input string is "B+", then comparing charAt(0) to 'B' is much different from using equalsIgnoreCase("B"), no? Of course that is far from the only thing that needs fixing, but it's certainly one of the things that needs fixing.

Courtney Over a year ago

I edited my code ONCE again. Now for some reason I can't get it to print out a value of -1 if a different input is entered. Any ideas?

Courtney Over a year ago

Nevermind I figured it out! Thanks for everyone's help!

Vineet · Accepted Answer · 2014-11-05 04:31:21Z

David's & Ken's answers are correct. You need to implement them both and then additionally remove some return statements, then the code will work as expected. Here's an example:

    if (Character.toUpperCase(grade.charAt(0)) == 'B')
        gradeNum = 3.0;
    if (grade.length() > 1 && Character.toUpperCase(grade.charAt(1)) == '-')
        gradeNum = gradeNum - 0.3;
    return gradeNum;

Earlier, since you're checking with grade.equalsIgnoreCase("B"), it would've never matched for an input as "B-". So, gradeNum would never have the value as 3.0. It would still be 0.0 and then perform gradeNum = gradeNum - 0.3; which results in -0.3.

Also, you could use a switch case instead of so many if statements. It'll be more elegant/readable & efficient.

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