我正在编写一个程序，作为电影商店的销售管理程序。它应该将.dat文件读入DVDmenu.java文件，它使用case / switch语句来处理菜单。我一直在编写和重写这个程序，但我似乎无法在我的代码中找到阻止它编译的链接错误。
import java.io.*; // this includes the input output library files
import java.util.*; // this includes the utility libraray files
public class DVDmenu
{
public static void main(String[] args)
{
Scanner scanF = null; // This creates an empty scanner for the .dat system.
PrintWriter pw = null; // This creates a print writer to write info to the .dat
String fileIn; // this creates the file input name of the .dat
LinkedList DVDinv = new LinkedList(); // this creates a linked list
if(args.length != 1)
{
System.out.println("USAGE: DVD Menu <input_file>");
System.exit(1);
}
fileIn = args[0];
try
{
scanF = new Scanner(new File(fileIn));
}
catch (FileNotFoundException e)
{
System.out.println("Error: file \"" + fileIn + "\" does not exist");
System.exit(2);
}
while(scanF.hasNext())
{
String title = scanF.nextLine();
DVD newDVD = new DVD(title);
DVDinv.insert(newDVD);
}
String input = "null";
System.out.println("Type a letter then press enter");
System.out.println("H:help,L:list,I:inquire, A:add, S:sell,Q:quit.");
scanF.close();
Scanner key = new Scanner(System.in);
do
{
char in = key.nextLine().charAt(0);;
switch(in)
{
case 'H':
case 'h':
System.out.println("Enter H for help, L to list, I <movieTitle> to"
+ " inquire, A <movieTitle> to add, S <movieTitle> to sell, M <amount>"
+ " <movieTitle> and Q to quit.");
break;
case 'L':
case 'l':
if(!DVDinv.isEmpty())
{
Node<DVD> head = DVDinv.getHead();
while(head != null)
{
System.out.println( head.getDVD().getStock() + " Has "
+ head.getDVD().getTitle() + "copies in stock.");
head = head.getNext();
}
}
break;
case 'I':
case 'i':
String title = input.substring(2);
DVD newDVD = new DVD(newDVD);
System.out.println(head.getDVD().getTitle() + " has "
+ head.getDVD().getStock() + " copies in stock.");
break;
case 'A':
case 'a':
String title = input.substring(2);
DVD newDVD = new DVD(title);
DVDinv.insert(newDVD);
System.out.println("One Copy of " + head.getDVD().getTitle() + " was added.");
break;
case 'S':
case 's':
String title = input.substring(2);
DVD newDVD = new DVD(title);
DVDinv.delete(newDVD);
System.out.println("All copies of " + head.getDVD().getTitle() + " have been sold.");
break;
case 'Q':
case 'q':
System.out.println("Thank you for using this system.");
break;
}
}while(in != 'Q' && in != 'q');
try
{
pw = new PrintWriter (new FileWriter(fileIn));
}
catch (IOException e)
{
System.out.println("General I/O exception: " + e.getMessage());
}
Node<DVD> current = DVDinv.getHead();
while(current != null)
{
for(int i=0; i < current.getDVD().getStock(); i++)
{
pw.println(current.getDVD().getTitle());
}current = current.getNext();
}pw.close();
}
}
public class DVD implements Comparable<DVD>
{
private String title; // this sets a private string variable for a movie
private int Stock; // this sets a private int variable for the amount
public DVD(String movieTitle)
{
title = movieTitle; // this sets the movie title to title
Stock = 1; // this automatically sets the # of copies to 1
}
public String getTitle()
{
return title; // this returns the movie title to the user
}
public int getStock()
{
return Stock; // returns the amount of films are available for sale
}
public void setStock(int newStock)
{
Stock = newStock; // adds inventory amount to available films for sale
}
public int compareTo(DVD DVDtoCompare)
{
return title.compareToIgnoreCase(DVDtoCompare.getTitle()); // compares two film title strings to
// determine which one is alphabetically above or below one another.
}
}
public class Node<DVD extends Comparable<DVD>>
{
private DVD dvd;
private Node<DVD> next;
public Node(DVD movieTitle)
{
dvd = movieTitle;
next = null;
}
public void setDVD(DVD newDVD)
{
dvd = newDVD;
}
public void setNext(Node<DVD> newNext)
{
next = newNext;
}
public DVD getDVD()
{
return dvd;
}
public Node<DVD> getNext()
{
return next;
}
}
public class LinkedList
{
private Node<DVD> head;
public LinkedList()
{
head = null;
}
public Node<DVD> contains(DVD thedvd)
{
Node<DVD> current = head;
while(current != null)
{
if(thedvd.compareTo(current.getDVD()) == 0)
{
return current;
}
else if(thedvd.compareTo(current.getDVD()) < 0)
{
return null;
}
else
{
current = current.getNext();
}
}
return null;
}
public void insert(DVD thedvd)
{
Node<DVD> toAdd = new Node<DVD>(thedvd);
if(this.isEmpty())
{
head = toAdd;
}
else
{
Node<DVD> current = head;
Node<DVD> previous = null;
while(current != null)
{
if(thedvd.compareTo(current.getDVD()) == 0)
{
current.getDVD().setStock(current.getDVD().getStock() + 1);
return;
}
else if(thedvd.compareTo(current.getDVD()) < 0)
{
toAdd.setNext(current);
if(previous != null)
{
previous.setNext(toAdd);
}
else
{
head = toAdd;
}
return;
}
else
{
previous = current;
current = current.getNext();
}
}
previous.setNext(toAdd);
}
}
public DVD delete(DVD thedvd)
{
if(this.isEmpty())
{
return null;
}
if (thedvd.compareTo(head.getDVD()) == 0)
{
if(head.getDVD().getStock() == 1)
{
head = head.getNext();
return thedvd;
}
else
{
head.getDVD().setStock(head.getDVD().getStock() - 1);
return thedvd;
}
}
Node<DVD> previous = head;
Node<DVD> current = head.getNext();
while(current != null)
{
if(thedvd.compareTo(current.getDVD()) == 0)
{
if(current.getDVD().getStock() == 1)
{
previous.setNext(current.getNext());
return thedvd;
}
else
{
current.getDVD().setStock(current.getDVD().getStock() - 1);
}
}
else if(thedvd.compareTo(current.getDVD()) < 0)
{
return null;
}
else
{
previous = current;
current = current.getNext();
}
}
return null;
}
public boolean isEmpty()
{
return (head==null);
}
public Node getHead()
{
return head;
}
public int getStock(DVD thedvd)
{
if(this.contains(thedvd) != null)
{
return ((this.contains(thedvd)).getDVD()).getStock();
}
return 0;
}
}
答案 0 :(得分：0)
您在head case 'L': case 'l':区块内创建变量if。它是一个局部变量，在此if块之外的任何位置都不可见，尤其是在您尝试访问它的下一个case 'I': case 'i':中不可见：
System.out.println(head.getDVD().getTitle() + " has "
+ head.getDVD().getStock() + " copies in stock.");