java程序编译得非常好，但在运行其drop时，字符串输入会出错

Question

程序编译得非常好，但在运行其drop时，UserInputWindows方法中的字符串输入出现错误。我以前写过一个类似这样的while循环，没有任何问题，但我似乎无法理解为什么它现在给了我一个错误。程序还远没有完成，我只是很快地运行它，看看是否有任何错误。下面是编码器

enter code here
import java.util.Scanner;

public class PaintEstimate
{
final static double WallAndCeilingPaintCost = 18.50;//cost for 1 gallon
//final static double WhiteEnamelPaintCost = 9.50; //cost for 1 quart//using only for refrence now//changed to _MoldingCostPerQuart 
//final static double ColorEnamelPaintCost = 12.50; //cost for 1 quart//using only for refrence now// changed to _MoldingCostPerQuart
final static double CoverageOfWallAndCeilingPaint = 250.00; // coverage of wall and ceiling paint in sqft
final static double CoverageOfEnamelPaint = 100.00;// coverage of enamel paint both color and whit in linear sqft

public static double IntchesToFeet;
public static double RoomSquareFeet, CeilingSqaureFeet;
public static double InchRoomWidth, InchRoomLength, InchRoomHeight;
public static double FeetRoomWidth, FeetRoomLength, FeetRoomHeight;
public static double NumberOfWindows, NumberOfDoors;
public static double InchesWindowsHeight, InchesWindowsLength, InchesWindowsMoldingWidth;
public static double InchesDoorsHeight, InchesDoorsLength, InchesDoorsMoldingWidth;
public static String WindowsMoldingColorOrWhite, DoorsMoldingColorOrWhite;
public static double WindowsMoldingCostPerQuart = 0;
public static double DoorsMoldingCostPerQuart = 0;
public static Scanner scan = new Scanner(System.in);

public static void main(String[] args) 
{
    Scanner scan = new Scanner(System.in);
    UserInputWallsAndCeiling();
    UserInputWindows();
    UserInputDoors();
}
public static void UserInputWallsAndCeiling()
{
    System.out.println("What is the room height in inches? ");
    InchRoomHeight = scan.nextDouble();
    System.out.println("What is the room width in inches? ");
    InchRoomWidth  = scan.nextDouble();
    System.out.println("What is the room length in inches? ");
    InchRoomWidth = scan.nextDouble();
}
public static void UserInputWindows()
{
    System.out.println("How many windows are in the room? ");
    NumberOfWindows = scan.nextDouble();
    if(NumberOfWindows > 0)
        {
            System.out.println("What are the windows height in inches? ");
            InchesWindowsHeight = scan.nextDouble();
            System.out.println("What are the windows length in inches? ");
            InchesWindowsLength = scan.nextDouble();
            System.out.println("What are the windows molding width in inches? ");
            InchesWindowsMoldingWidth = scan.nextDouble();
            System.out.println("Is the windows molding color or white? ");

            boolean WindowsTrue = false;
            while (!WindowsTrue)
                {
                    System.out.println("Is the doors molding color or white? ");
                    DoorsMoldingColorOrWhite = scan.nextLine();
                    if ( WindowsMoldingColorOrWhite.equals("color"))
                        {
                            WindowsMoldingCostPerQuart = 12.50; 
                            WindowsTrue = true;
                        }
                    else if (WindowsMoldingColorOrWhite.equals("white"))
                        {
                            WindowsMoldingCostPerQuart = 9.50;
                            WindowsTrue = true;
                        }
                    else
                        {
                            System.out.println("Please enter if the molding is color or white");
                        }
                }
        }
}
public static void UserInputDoors()
{
    System.out.print("How many doors are in the room? ");
    NumberOfDoors = scan.nextDouble();
    if(NumberOfDoors > 0)
        {
            System.out.println("What are the doors height in inches? ");
            InchesDoorsHeight = scan.nextDouble();
            System.out.println("What are the doors length in inches? ");
            InchesDoorsLength = scan.nextDouble();
            System.out.println("What are the doors molding width in inches? ");
            InchesDoorsMoldingWidth = scan.nextDouble();

            boolean DoorsTrue = false; 
            while (!DoorsTrue)
                {
                    System.out.println("Is the doors molding color or white? ");
                    DoorsMoldingColorOrWhite = scan.nextLine();
                    if ( DoorsMoldingColorOrWhite.equals("color"))
                        {
                            DoorsMoldingCostPerQuart = 12.50;
                            DoorsTrue = true;
                        }
                    else if (DoorsMoldingColorOrWhite.equals("white"))
                        {
                            DoorsMoldingCostPerQuart = 9.50; 
                            DoorsTrue = true;
                        }
                    else
                        {
                            System.out.println("Please enter if the molding is color or white");
                        }
                 }
            //System.out.print(InchesDoorsHeight + " " + InchesDoorsLength + " " + DoorsMoldingColorOrWhite + " " + DoorsMoldingCostPerQuart)
        }
}
public static void IntchesToFeet()
{
    FeetRoomWidth= InchRoomWidth / 12;
    FeetRoomLength = InchRoomLength / 12;
    FeetRoomHeight = InchRoomHeight / 12;
}

}

Answer 1

这是一个简单的打字错误；）

System.out.println("Is the doors molding color or white? ");
DoorsMoldingColorOrWhite = scan.nextLine();
if ( WindowsMoldingColorOrWhite.equals("color")) {
        //...
}

门成型与窗成型

如果检查由此产生的NullPointerException，则代码#61的行直接指向If语句，该语句告诉您在该行或之前开始搜索：

线程“main”java中出现异常。lang.NullPointerException在PaintEstimate。UserInputWindows（PaintEstimate.java:61）