java - 找不到符号错误

Question

我有点迷茫；我觉得我之前已经做过类似的事情，但这是行不通的。我忘记了一些调整吗？由于某种原因，它说它找不到下面的三个变量，我是否需要将它们移到其他位置/在方法中声明/以某种方式使方法与变量调用脱节？所有帮助，不胜感激。

Scanner input = new Scanner(System.in);
        int atmId, selection;
        double atmVal;
    selectId();

        switch(selection){
            case 1:  AccArray[atmId].getBalance();
                    break;
            case 2: System.out.print("How much would you like to withdraw? ");
                    atmVal=input.nextInt();
                    AccArray[atmId].withdraw(atmVal); 
                    break;
            case 3:  System.out.print("How much would you like to deposit? ");
                    atmVal=input.nextInt();
                    AccArray[atmId].deposit(atmVal);
                    break; 
            case 4:  selectId();
                    break;
        }


    } // End of main method

// Method for id selection
    public static void selectId(){
// Allows for and requests user input       
        System.out.print("Enter an id: ");
        atmId = input.nextInt();

// Checks for valid input       
        while (atmId>9 || atmId<0){
            System.out.println("Invalid id.");
            System.out.print("Enter an id (0-9): ");
            atmId = input.nextInt();
        }
        displayMenu();
    }

// Method to display menu
    public static void displayMenu(){
        System.out.println("Main menu");
        System.out.println("1: check balance");
        System.out.println("2: withdraw");
        System.out.println("3:deposit");
        System.out.println("4:exit");
        System.out.print("Enter a choice ");
        selection = input.nextInt();
        // Checks for valid input
         while (selection>4 || selection<1){
            System.out.println("Invalid choice.");
            System.out.print("Enter a choice (1-4): ");
            selection = input.nextInt();
        }
    }
} // End of Test class

Answer 1

请注意，您存在一些范围界定错误-在方法内部声明的变量仅在该方法内可见，而在其他方法中不可见。为了解决这个问题，您可以在类中声明变量。

例如，仅使用静态字段和方法:

public class Foo {
  private static int bar; // I am visible throughout the class

  public static void someMethod() {
    int baz = 8;  // I've declared a *local* variable here
  }

  public static void anotherMethod() {
    bar = 3;  // I can use bar here since it's visible throughout

    baz = 7; // this won't compile since baz is visible only within someMethod()
  }
}

话虽如此，但是您的selectId()方法不应该返回一个int吗？然后，您不应该将返回的int分配给选择变量吗？如果这样做，则不必在类中声明选择变量。

请注意，我将让displayMenu()做到这一点-显示菜单，并且不会让它得到用户输入。那将是selectId()方法要做的。