i must write a programm that it translate grade in letter form like as A, B, C, D or F into number form (4, 3, 2, 1, 0 respective). The grade can have + or - too (+ increase grade of 0.3, - decrease of same number). I wrote this programm:  public class Grade{    private String letterGrade;    private String letter;    private String symbol = "n";    private double numericGrade;    private double grade;    private final double PLUS = 0.3;    private final double MENO = -0.3;     public Grade(String letterGrade) {       this.letterGrade = letterGrade;    }     public double getNumericGrade() {       if (letterGrade.length() &gt; 1) {          letter = letterGrade.substring(0, 1);          symbol = letterGrade.substring(1, 2);       }        if (letter.equals("A")) {          numericGrade = 4.0;           if (symbol.equals("+")) {             symbol = "n";          }       }       else if (letter.equals("B")) {          numericGrade = 3.0;       }       else if (letter.equals("C")) {          numericGrade = 2.0;       }       else if (letter.equals("D")) {          numericGrade = 1.0;       }       else if (letter.equals("F")) {          numericGrade = 0.0;       }        if (symbol.equals("+")) {          grade = numericGrade + PLUS;       }       else if (symbol.equals("-")) {          grade = numericGrade + MENO;       }       else {          grade = numericGrade;       }        return grade;    } }   And the programm tester:  import java.util.Scanner; public class GradeTester{     public static void main(String[] args) {         Scanner in = new Scanner(System.in);          System.out.print("Please enter the grade in letter form: ");         String letterGrade = in.next();          if (letterGrade.equals("A") || letterGrade.equals("A+") || letterGrade.equals("A-")) {             Grade graduation = new Grade(letterGrade);              System.out.println("The grade in number form is: " + graduation.getNumericGrade());         }         else if (letterGrade.equals("B") || letterGrade.equals("B+") || letterGrade.equals("B-")) {             Grade graduation = new Grade(letterGrade);              System.out.println("The grade in number form is: " + graduation.getNumericGrade());         }         else if (letterGrade.equals("C") || letterGrade.equals("C+") || letterGrade.equals("C-")) {             Grade graduation = new Grade(letterGrade);              System.out.println("The grade in number form is: " + graduation.getNumericGrade());         }         else if (letterGrade.equals("D") || letterGrade.equals("D+") || letterGrade.equals("D-")) {             Grade graduation = new Grade(letterGrade);              System.out.println("The grade in number form is: " + graduation.getNumericGrade());          }         else if (letterGrade.equals("F")) {             Grade graduation = new Grade(letterGrade);              System.out.println("The grade in number form is: " + graduation.getNumericGrade());         }         else {             System.out.println("Not permissed!");         }     } }   But when i'm try it, only for letter without + or - this error appear:  Exception in thread "main" java.lang.NullPointerException         at Grade.getNumericGrade(Grade.java:20)         at GradeTester.main(GradeTester.java:13)   I don't understand what's the problem.
What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?
Optimal drive configuration for SQL Server 2008R2 I have a fairly busy database server running SQL Server 2008 R2 that has the following setup:   SATA RAID 1 (2 Drives)  - OS / Programs SAS  RAID 10 (4 Drives) - Sql Database Files (data and logs) SAS  RAID 1 (2 Drives)  - TempDB (data and logs)   Assuming I can't add additional drives into this server, have I made the best use of the configuration I have available? Or should I consider another scheme here where logs are isolated from the data files, for example?  Update:  For those that requested further hardware details:   The SATA drives (used for the OS / Program partition) are: WD 7200 RPM 3 Gb/s 3.5 Inch SATA The SAS drives used in the other arrays are: Seagate 15K RPM 6 Gb/s 3.5 inch SAS The RAID controller used is an: LSI 9260-8i SAS/SATA 6 Gb 8 port   Update 2:  Based upon the feedback I've received, it looks like I have the following viable options to choose from - I will award the bounty to someone that can tell me which is likely to be the best in the environment that I've outlined:   Leave everything as is - I probably won't do much better  Move my 2 SAS RAID 1 drives into my existing RAID 10 array to have it composed of 6 disks in total  Move my log files onto the SAS RAID 1 and/or relocate TempDB (data or logs) back to the RAID 10 Examples  I've recently found examples of using pairs of enclosing braces {}, with nothing in between the opening and closing braces, as arguments to commands and even to their options:  cat foo | xargs -I{} echo {}  find . -size 0 -exec rm -i {} \;  No Documentation  My problem is that I cannot find a documentation in the  that describes the usage of {} in such context as in the examples above.  I do not think it is a , because a dollar sign must precede the enclosing braces in a parameter expansion as in ${}.  It cannot be a  either, because it takes the form of {x..y[..incr]}, where x and y are not optional.  It also cannot be a  either, because {} is used as arguments.  Questions   What does a pair of enclosing braces {} even mean, in general, as an argument to any command that accepts it? Where can I find a documentation that describes the usage of {} as arguments? Is temperature a Lorentz invariant in relativity? I used to say "sharp sign" to refer to the # sign.   Today a friend told me that the correct term is number sign or hash sign or even just hash.  What is the difference between these options and what's the correct usage of the names for this sign? 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Forming the plural possessive in such a case is rather simple.  I encountered a more complex use of this recently - referring to a single house owned by a single family in a set of houses owned by a set of families.  We can say "the families' houses" to refer to all of the houses owned by all of the families.  We can say "one of the families' houses" to refer to one of the houses owned by one or more of the families. In this context, "one of" applies to "the families' houses".  If we were instead to apply "one of" to "the families", and want to refer to the one house owned by "one of the families", how would this be written?  My first though was "one of the families's house", taking "one of the families" as a single noun and appending 's to it. This looks (and sounds) a bit strange, though. "One of the families' house" and "one of the family's house"/"one of the family's houses" seem wrong to me, and I can't really determine the correct way to say/write this.  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