Question

正如您所看到的，我正在创建一个文件并从中读取信息，然后将该信息分配给变量，以便我可以使用它来执行操作。有人可以帮我理解为什么我的编译器说像deskQuantity，lampPrice，theName等可能没有初始化？

谢谢！

/**
Add in javadoc comments
*/


//import statements
import java.io.*;
import java.util.*;

public class Try2 { 
    public static void main(String[] args){
        //variables
        Scanner kb = new Scanner(System.in);
        boolean valid = false;
        int mainSelect = 0;
        int itemOption = 0;
        boolean valid2 = false;
        boolean returnToMain = false;
        String theName;
        double thePrice;
        int theQuantity;
        double currBal;
        String lampName;
        double lampPrice;
        int lampQuantity;
        String chairName;
        double chairPrice;
        int chairQuantity;
        String deskName;
        double deskPrice;
        int deskQuantity;

        //create file
        try{
            PrintWriter outputFile = new PrintWriter("inventory.txt");
            outputFile.println("3000.0");
            outputFile.println("Lamps 15.3 400");
            outputFile.println("Chairs 19.95 250");
            outputFile.println("Desks 95.0 300");
            outputFile.close();
        }
        catch(IOException e){
            System.out.println("File cannot be created.");
        }

        //read data in from file
        try{
            File file = new File("inventory.txt");
            Scanner inFile = new Scanner(file);
            currBal = inFile.nextDouble();
            lampName = inFile.next();
            lampPrice = inFile.nextDouble();
            lampQuantity = inFile.nextInt();
            chairName = inFile.next();
            chairPrice = inFile.nextDouble();
            chairQuantity = inFile.nextInt();
            deskName = inFile.next();
            deskPrice = inFile.nextDouble();
            deskQuantity = inFile.nextInt();
            inFile.close();
        }
        catch(FileNotFoundException e){
            System.out.println("Cannot find file.");
        }


        //present user with main menu
        do{
        System.out.println("Current Balance: $" + currBal);
        System.out.println("\t1. " + lampName  + "\t\t(" + lampQuantity +  " at $" + lampPrice + ")");
        System.out.println("\t2. " + chairName + "\t\t(" + chairQuantity +  " at $" + chairPrice + ")");
        System.out.println("\t3. " + deskName + "\t\t(" + deskQuantity +  " at $" + deskPrice + ")");
        System.out.println("\t0. Exit");

        while(valid == false){
            System.out.print("\nPlease enter choice: ");
            try{
                mainSelect = kb.nextInt();
                if(0 <= mainSelect || mainSelect >=  3){
                    valid = true;
                }
                else{
                    System.out.println("That is not a valid selection. Try again.");
                }
            }
            catch(InputMismatchException ime){
                System.out.println("That is not a valid selection. Try again.");
                kb.next();
            }
        }
        //present user with second menu
        switch(mainSelect){
            case 1:
                theQuantity = lampQuantity;
                thePrice = lampPrice;
                theName = lampName;
                break;
            case 2:
                theQuantity = chairQuantity;
                thePrice = chairPrice;
                theName = chairName;
                break;
            case 3:
                theQuantity = deskQuantity;
                thePrice = deskPrice;
                theName = deskName;
                break;
            case 0:
                System.exit(0);
                break;
        }
        System.out.println("Current balance: $" + currBal);
        System.out.println("Current Quantity: " + theQuantity);
        System.out.println("Current price: $" + thePrice);
        System.out.println("1. Sell " + theName);
        System.out.println("2. Buy " + theName);
        System.out.println("3. Change price");
        System.out.println("0. Return to main menu");

        while(valid2 == false){
            System.out.print("\nPlease enter choice: ");
            try{
                itemOption = kb.nextInt();
                if(0 <= itemOption || itemOption >=  3){
                    valid2 = true;
                }
                else{
                    System.out.println("That is not a valid selection. Try again.");
                }
            }
            catch(InputMismatchException ime){
                System.out.println("That is not a valid selection. Try again.");
                kb.next();
            }
        }
    }while(returnToMain == true);
    }
}

Answer 1

编译器警告您正在尝试使用可能没有任何值的变量。

您可以像这样创建办公桌数量：

int deskQuantity;

然后你尝试为它赋值（在try {}块中）

 try{
            File file = new File("inventory.txt");
            Scanner inFile = new Scanner(file);
            currBal = inFile.nextDouble();
            lampName = inFile.next();
            lampPrice = inFile.nextDouble();
            lampQuantity = inFile.nextInt();
            chairName = inFile.next();
            chairPrice = inFile.nextDouble();
            chairQuantity = inFile.nextInt();
            deskName = inFile.next();
            deskPrice = inFile.nextDouble();
            deskQuantity = inFile.nextInt();
            inFile.close();
        }

然后你会像这样打印出来：

System.out.println("\t3. " + deskName + "\t\t(" + deskQuantity +  " at $" + deskPrice + ")");

但是如果try块失败，则永远不会设置该值。您可以通过设置默认值（初始化）来避免此警告：

String deskName = "";
int deskQuantity = 0;

但是你也应该注意处理未设置的值或其他故障。您已经检查过是否找不到该文件。您还应该在此处捕获其他异常，如果您发现任何异常，可能会停止处理：

catch(FileNotFoundException e){
    System.out.println("Cannot find file.");
} catch(Exception e) {
    System.out.println("Caught Exception: " + e.getLocalizedMessage() );
}

Answer 2

如果Scanner inFile = new Scanner(file);或第二个try块中的任何其他行引发异常，则程序会捕获它，并继续尝试显示菜单。

但是菜单代码指的是在这种情况下不会给出值的变量。编译器阻止您执行此操作，并强制您确保这些变量具有值。

最好将菜单代码移到第二个try块中，这样如果从Scanner读取值的代码失败，它就不会运行。

试图从文件导入信息，但数据“可能尚未初始化”？

2 个答案: