Question

目标是为ATM对象创建帐户注册方法。但我一直打破用于进入循环的if语句。我认为我的“措辞”是关闭的，但我在如何解决这个问题上留下了空白。有什么建议？问题本身位于if(acc[i].getAcc()==0)，其中.getAcc是类中的getter。

package atmassignment;

import java.util.Scanner;
public class AtmAssignment {
static Scanner in = new Scanner(System.in);
static int cou = 1;
static Account[] acc = new Account[10];

    public static void main(String[] args) {
        menu();
    }
    public static void menu(){
        char opt;
        System.out.println("Thanks for accessing ATManager.");
        System.out.println("Please select a menu option to proceed.");
        System.out.println("1-Register a new account, 2-Access an account, 0-Exit ATManager");
        opt = in.next().charAt(0);

        switch (opt) {
            case '1':
                newAccount();
                break;

            case '2':
                selAccount();
                break;

            case '0':
                System.out.println("Goodbye.");
                break;

            default:
                System.out.println("Invalid Entry.");             
                break;
        }
    }
    public static void newAccount(){
        System.out.println("Account registration");
      for (int i = 0; i < acc.length; i++){
          if(acc[i].getAcc()==0){
              System.out.println("Please enter your first name...");
              String fn = in.next();
              System.out.println("Please enter your last name...");
              String ln = in.next();
              System.out.println("Please enter your address...");
              String ad = in.next();
              System.out.println("Please provide a contact number...");
              String cn = in.next();
              Customer cus = new Customer(fn, ln,ad,cn);
              System.out.println("What is your starting balance...");
              double bal = in.nextDouble();
              acc[i] = new Account(cou, bal, cus);
              System.out.println("Your account is registered as ID#"+cou);
              break;           
          } else {
                System.out.println("Sorry, no more accounts can be created.");
                break;
            }
      }
    }



}

Answer 1

这会分配一个对象引用数组：

static Account[] acc = new Account[10];

但是它实际上并没有分配任何对象，因此当您尝试访问第一个元素时，可能会获得空指针异常。在您的初始化代码中，执行以下操作：

for(int i = 0; i < 10; i++)
    acc[i] = new Account();

Answer 2

在实际构建对象之前调用acc[i].getAcc()==0。也许修改for循环以便创建对象，然后使用setter方法收集输入并更新对象？这当然要求您为Account类提供某种默认构造函数。

acc[j through maxLength] = new Account(); //where j spans the entire length of the array
for (int i = 0; i < acc.length; i++){
          if(acc[i].getAcc()==0){
              System.out.println("Please enter your first name...");
              String fn = in.next();
              System.out.println("Please enter your last name...");
              String ln = in.next();
              System.out.println("Please enter your address...");
              String ad = in.next();
              System.out.println("Please provide a contact number...");
              String cn = in.next();
              Customer cus = new Customer(fn, ln,ad,cn);
              System.out.println("What is your starting balance...");
              double bal = in.nextDouble();
              acc[i].setContact(###);
              acc[i].setBalance(###); //ETC
              System.out.println("Your account is registered as ID#"+cou);
              break;           
          } else {
                System.out.println("Sorry, no more accounts can be created.");
                break;
          }
}

Answer 3

可能您没有填充您的Account []数组。在这里，我只能看到你声明你的数组 -

static Account[] acc = new Account[10];

所以在那之后，当你试图使用for循环获取数组元素时，你无法访问它们。您在if(acc[i].getAcc()==0)这一行收到错误。因此，我建议您删除if if，因为您在此行后面填写了帐户 - acc[i] = new Account(cou, bal, cus);

希望它会有所帮助非常感谢。

无法进入循环

3 个答案: