Java - 变量作用域

Question

我是java新手，我有一个 super n00bish问题。 (我确实有一些一般的编程知识)。我试图访问变量“item”但无济于事。有人能找出原因吗？

    public void start() 
    {
        Scanner input = new Scanner(System.in);

        System.out.println("Enter saleman's name: ");
        String name = input.next();

       int exit = 0;
       do 
       {
           System.out.println("Enter item number: ");
           String item = input.next();
           if (ValidateItem(item) == true)
           {
               if (Integer.parseInt(item) <=4 && Integer.parseInt(item) >=1)\
               {
                   exit = 1;
               }
               else 
                   System.out.println("Enter an item number between 1 and 4");
           }

           if (ValidateItem(item) == false)
           {
                System.out.println("Enter an item number between 1 and 4");
           }

       } while (exit == 0);

       int exitQuan = 0;
       do 
       {
           System.out.println("Enter quantity (1-99): ");
           String quant = input.next();
           if (ValidateItem(quant) == true)
           {
                exitQuan = 1;
           }
           else 
               System.out.println("Enter a quantity between 1 and 99");
       } 
       while (exitQuan == 0);

       if (item == 1) 
       {
           pay = 239.99;
       }

最后一个 IF 语句是我缺乏范围的地方。谢谢。

Answer 1

变量作用域仅扩展到声明周围的最小大括号对。例如:

//this could be a method body, an if statement, a loop, whatever
{
    int x;
} //x passes out of scope here

因此，当您在 do-while 循环内声明 item 时，一旦退出循环，其作用域就会结束。要解决此问题，请在循环上方声明 item，如下所示:

String item = null; //initialize to null to avoid warning about using an un-initialized variable

do {
    System.out.println("Enter item number: ");
    item = input.next();

    //rest of loop...

} while (exit == 0);

这样，item 将一直可用，直到该方法返回。