Calling a method from a different class to another

问题:

I have two classes, one called Driver and another called BankAccount. In Driver there is a method called Driver, and in BankAccount a method called Deposit. I'm getting an error that says, "non-static method Deposit() cannot be referenced from a static context" when I try to call BankAccount.Deposit from my Driver method.

Any advice on what I should do to these lines of code to make it run.

 import javax.swing.JOptionPane;
public class Driver
{
    int choice;
    String number;
    //public Driver()
    public Driver()
    {
         String number = JOptionPane.showInputDialog("1. Deposit 2. Withdraw 3. Balance 4. Change name 5. Exit");
         int choice = Integer.parseInt(number);
         do
         {
         if( choice == 1)
         {
             BankAccount.Deposit() = new Deposit();
             Driver.Driver = new Driver();
            }else if(choice == 2)
          {
              BankAccount.Withdrawl = new Withdrawl();
              Driver.Driver = new Driver();
            }else if(choice == 3)
            {
               BankAccount.getBalance = new getBalance();
               JOptionPane.showDialog(balance);
               Driver.Driver = new Driver();
            }else if(choice == 4)
            {
                name = JOptionPane.showInputDialog(" Please enter a name");
                Driver.Driver = new Driver();
            }else if(choice ==5)
            {
                JOptionPane.showDialog("Goodbye" + name);
            }
        }while( choice >= 1 && choice <= 5);
}
}

here is the BankAccount Method

 import javax.swing.JOptionPane;
public class BankAccount
{
double balance = 400;
double deposit;
double withdraw;
double Interest = 1.05;
String name;
String accountNumber;

public BankAccount()
{
name = null;
accountNumber = null;
balance = 0;
}

public double Deposit()
{
    String input = JOptionPane.showInputDialog("How much would you like to deposit?");
    deposit = Integer.parseInt(input);
    if (deposit < 10000)
    {
        balance = (deposit + balance);

    }
    return balance;
}

}

回答1:

I don't understand why you have written your code like this.

Method name in java should start with a small letter like deposit and not Deposit.

BankAccount is a class and Deposit is a non-static method in it.

So for using Deposit method you must first create an object/instance of your BankAccount class like this :

BankAccount b =new BankAccount();

And then use any method using that object reference :

b.Deposit();
b.Withdraw();

You should write it like this :

if( choice == 1)
{
     BankAccount b = new BankAccount();
     b.Deposit();
}

Same you need to do for withdraw and other

else if(choice == 2)
{
     BankAccount b = new BankAccount();
     b.Withdrawl();
     Driver.Driver = new Driver();
}

回答2:

This statement:

BankAccount.Deposit() = new Deposit();

makes no sense. First, Deposit() is an instance method of BankAccount. It only makes sense to call it for a particular instance of BankAccount. That's what the compiler is complaining about.

Beyond that, there's the problem that Deposit() returns an int value, which is not something that can appear on the left side of an assignment statement. Also, you don't mention any class named Deposit, so I don't know what new Deposit() is supposed to be.

You seem to have similar problems further on in your code. For instance, the next statement:

Driver.Driver = new Driver();

is utter nonsense—there is no field Driver.Driver.

I recommend that you read the tutorial Understanding Instance and Class Members.

回答3:

a working version of your 'intention' :

import javax.swing.JOptionPane;
public class Driver
{
    int choice;
    String number;
    BankAccount myAccount=null;

    public Driver()
    {
    myAccount=new BankAccount();
    }

    public void drive()
    {
    String number = "";
        int choice = 0;
        String name = "?";
         do
         {
             number = JOptionPane.showInputDialog("1. Deposit 2. Withdraw 3. Balance 4. Change name 5. Exit");
             choice = Integer.parseInt(number);
         if( choice == 1)
         {
             myAccount.Deposit();
            }else if(choice == 2)
          {
          // mAccount.Withdrawl();
          // missing method Withdraw1()
            }else if(choice == 3)
            {
        // BankAccount.getBalance = new getBalance();
        // missing method getBalance()
        // JOptionPane.showDialog(balance);
            }else if(choice == 4)
            {
                JOptionPane.showInputDialog(" Please enter a name");
        // todo i guess name should be used somewhere in bankaccount... like myAccount.setName(name)
            }else if(choice ==5)
            {
                // JOptionPane.showDialog("Goodbye" + name);
        // no showDialog method in JOptionPane
        return;
            }
        }while( choice >= 1 && choice <= 5);
    }

    public static void main(String pArgs[])
    {
    Driver driver=new Driver();
    driver.drive();
    }
}