找不到符号方法 - 我应该在哪里定义我的方法？ [复制]

Question

我正在用 Java 编写一个银行程序，但在正确调用我的几个方法时遇到了一些麻烦。当我尝试编译我的文件时，这些是我得到的错误：

MustangBanking.java:74: error: cannot find symbol
            displayAccounts();
            ^
  symbol:   method displayAccounts()
  location: class MustangBanking

MustangBanking.java:75: error: cannot find symbol
            deleteAccount();
            ^
  symbol:   method deleteAccount()
  location: class MustangBanking
2 errors

我的包中的两个相关文件（此处仅粘贴相关部分）是 MustangBanking.java：

public class MustangBanking {

public static void main(String[] args) {

    //Declare and initialize data fields
//irrelevant code
case 3:
    displayAccounts();
    deleteAccount();
    break;
//more irrelevant code

和 Account.java

public class Account {

//Declare and initialize data fields
//irrelevant code
    public void deleteAccount() {
        //method code
    }
    public void displayAccounts() {
        //method code
    }
//irrelevant code

我在其他地方读到我的问题是，这两个方法应该在 MustangBanking 类而不是 Account 类中定义，并且它们应该在 main 方法之外定义。但是当我这样做时，我会收到无法找到所有变量等的错误。我在这里忘记了什么？如果您需要更多代码/说明，请告诉我，我会发布。

谢谢！

编辑： MustangBanking 类

import java.util.*;
import java.io.*;

//MustangBanking class
public class MustangBanking {

public static void main(String[] args) {

    //Declare and initialize data fields
    int id = 1000;
    double depositAmount = 0.0;
    double withdrawAmount = 0.0;
    double checkAmount = 0.0;
    double balance = 0.0;
    double annualInterestRate = 0.0;
    boolean run = true;
    int option;
    Scanner in = new Scanner(System.in);
    Account account = new Account();

    //Create ArrayList of type Account to store all Account objects
    ArrayList<Account> accounts = new ArrayList<>();

    //Loop to run the program inside of
    while (run) {

        //Display the menu
        System.out.println("\nMUSTANG BANKING MENU");
        System.out.println("\n1 -- Create a new checking account");
        System.out.println("2 -- Create a new savings account");
        System.out.println("3 -- Delete an existing account");
        System.out.println("4 -- View a specific account");
        System.out.println("5 -- View all accounts");
        System.out.println("6 -- Write checks for a checking account");
        System.out.println("7 -- Deposit funds into an account");
        System.out.println("8 -- Withdraw funds from an account");
        System.out.println("9 -- Find account with the largest balance");
        System.out.println("10 -- Exit");
        System.out.println("\nEnter Option:");
        option = in.nextInt();

        //Switch statement to direct program based on option entered by user
        switch (option) {

            //create a new checking account
            case 1:
            CheckingAccount c1 = new CheckingAccount(id, balance, annualInterestRate); //Create a new CheckingAccount object
            id++; //increment id by 1
            accounts.add(c1); //add the new CheckingAccount to the Arraylist accounts
            break;

            //create a new savings account
            case 2:
            SavingsAccount s1 = new SavingsAccount(id, balance, annualInterestRate); //create a new SavingsAccount object
            id++; //increment id by 1
            accounts.add(s1); //add the new SavingsAccount to the ArrayList accounts
            break;

            //delete an existing account
            case 3:
            //c1.displayAccounts();
            //c1.deleteAccount();
            break;

- 帐号类

import java.util.*;
import java.io.*;

//Account class
public class Account {

//Declare and initialize data fields
protected int id = 1000;
protected double balance = 0.0;
protected double annualInterestRate = 0.0;
protected double monthlyInterestRate;
protected Date dateCreated;
protected double depositAmount = 0.0;
protected int pendingChecks = 0;

Scanner in = new Scanner(System.in);

//Create ArrayList of type Account to store all Account objects
ArrayList<Account> accounts = new ArrayList<>(); //do i need to create the arraylist in every class?

//Delete account
public void deleteAccount() {
    System.out.println("\nPlease enter the ID of the account you wish to delete:");
    id = in.nextInt(); //take user input of id to delete
    accounts.remove(id); //remove the account
}

//Display all accounts
public void displayAccounts() {
    System.out.println("\nAvailable accounts:\n");
    for (int i = 0; i < accounts.size(); i++) {
        System.out.println(accounts.get(i).getId()); //print the id instead of the index
    }
}

//Display one account
public void displayAccount() {
    //Prompt user for the account they want to view
    System.out.println("\nPlease enter the ID of the account you would like to view:");
    id = in.nextInt();

    //Print the account information
    for (int i = 0; i < accounts.size(); i++) {
        if (accounts.get(i).getId() == id) {
            //if savings account
            if (accounts.get(i) instanceof SavingsAccount) { 
                System.out.println("Account type: Savings");
            }
            //if checking account
            else if (accounts.get(i) instanceof CheckingAccount) {
                System.out.println("Account type: Checking");
            }
        }
    }
    System.out.println("Account: " + id); //Print ID
    System.out.println("Balance: " + balance); //Print balance
    System.out.println("Date created: " + dateCreated); //Print date created
    System.out.println("Annual interest rate: " + annualInterestRate + "%"); //Print annual interest rate   
    //if checking account, print number of pending checks
    for (int i = 0; i < accounts.size(); i++) {
        if (accounts.get(i).getId() == id) {
            if (accounts.get(i) instanceof CheckingAccount) {
                System.out.println("Number of pending checks: " + pendingChecks);
            }
        }
    } 
}

Answer 1

您在MustangBanking 类中调用Account 类的方法，而不使用Account 类的对象。这是导致问题的原因。

尝试更改以下主要方法代码：

public static void main(String[] args) {
    Account account = new Account();
    //Declare and initialize data fields
    //irrelevant code

    case 3:
        account.displayAccounts();
        account.deleteAccount();
        break;
    //more irrelevant code

帐户类别 将以下方法添加到 Account 类

public void add(Account a){
    accounts.add(a)
}

从所有的 switch case 中调用这个方法：

    //Switch statement to direct program based on option entered by user
    switch (option) {

        //create a new checking account
        case 1:
        CheckingAccount c1 = new CheckingAccount(id, balance, annualInterestRate); //Create a new CheckingAccount object
        id++; //increment id by 1
        account.add(c1); //add the new CheckingAccount to the Arraylist accounts
        break;

        //create a new savings account
        case 2:
        SavingsAccount s1 = new SavingsAccount(id, balance, annualInterestRate); //create a new SavingsAccount object
        id++; //increment id by 1
        account.add(s1); //add the new SavingsAccount to the ArrayList accounts
        break;

        //delete an existing account
        case 3:
        //c1.displayAccounts();
        //c1.deleteAccount();
        break;

删除方法

//Delete account
public void deleteAccount() {
     System.out.println("\nPlease enter the ID of the account you wish to    delete:");
     id = in.nextInt(); //take user input of id to delete
     Iterator<Account> iAccount = accounts.iterator();
     while(iAccount.hasNext()){
          Account account = iAccount.next();
          if(account.getId()==id){
                accounts.remove(account);
          }
     }
 }

Answer 2

您在没有创建 Account 类的对象的情况下调用 displayAccounts() 和 deleteAccount()，因此您收到了错误

使用对象调用方法有两种方式。

1. 如果方法在同一个类中
2. 如果有继承（MustangBanking extends Account）

如果您在 Account 类中没有任何其他方法，则可以直接扩展 Account

另外，在 MustangBanking 类中创建一个 Account 对象，然后调用上述方法如下

Account account =new Account ();
account.displayAccounts();
account.deleteAccount();