无法调用打印方法

Question

在我的代码中，我需要它来接受字母等级，然后它会打印出相应的数字值。我遇到的问题是我无法弄清楚如何正确地调用方法。我觉得我很接近，但对于做什么很困惑。

public class Grade
{
    public static void main( String[ ]  args)
   {
    Scanner input = new Scanner(System.in);
    System.out.print("Enter a letter grade: ");
    String letterGrade = input.nextLine();
    Grade number = new Grade(letterGrade);
    double grade = number.getNumericGrade();

    System.out.println("The numberic value is: " 
                       + grade);

    }


public double getNumericGrade(String letterGrade)
    {
        double numericGrade = 0.0;
    if ((letterGrade == "A") || (letterGrade == "A+"))
        numericGrade = 4.0;
    else if (letterGrade == "A-")
        numericGrade = 3.7;
    else if (letterGrade == "B+")
        numericGrade = 3.3;
    else if (letterGrade == "B")
        numericGrade = 3.0;
    else if (letterGrade == "B-")
        numericGrade = 2.7;
    else if (letterGrade == "C+")
        numericGrade = 2.3;
    else if (letterGrade == "C")
        numericGrade = 2.0;
    else if (letterGrade == "C-")
        numericGrade = 1.7;
    else if (letterGrade == "D+")
       numericGrade = 1.3;
    else if (letterGrade == "D")
        numericGrade = 1.0;
    else if (letterGrade == "D-")
        numericGrade = 0.7;
    else if (letterGrade == "F")
        numericGrade = 0.0;
    else 
        numericGrade = -1;
        return numericGrade;
    }     
}