Question

需要案例5＆amp; 7.

5显示所有对象＆amp;相关变量=（日期/帐号＃/ 1行上的名称+地址下四行+最后一行的余额。

我不知道如何嵌套方法来执行上述操作/格式化输出。

这看起来应该但是一直给我java lang空指针异常

  if(!db.list.isEmpty())
      { 
        for (int i = 0; i < db.list.size(); i++) 
        { 
        String s = " ";    
        s = "hello  123  "+db.getaccount().getcustomer().getAccountNumber()
            +"\nBalance is: "+db.getaccount().balance;

        JTextArea text = new JTextArea(s, 6, 20);
        JScrollPane pane = new JScrollPane(text);
        JOptionPane.showMessageDialog(null, pane,
        "Current Customers List", JOptionPane.INFORMATION_MESSAGE);
        }}break;

非常感谢任何帮助/建议。提前致谢，完整代码

       package bankaccount;

import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;

    public class BankAccountTest 
    {
    public static void main (String[] args)
    {
        Database db = new Database();
        Database deleted = new Database();
        boolean done = false;
        while (!done)

        {
            int activity = IO.getInt("Please choose one of the following:"+
             "\n 1 to create new account"+ "\n 2 to delete an account"+
            "\n 3 to withdraw from an account"+"\n 4 to deposit to an account"+
             "\n 5 to list all customers"+"\n 6 to list all deleted customers"+
             "\n 7 to display single account "+"\n 8 to exit this program");

        switch(activity)
        {

      case 1:

      //Create new account
      String LastName = IO.getString("Please type last name: ");
      String FirstName = IO.getString("Please type first name: ");
      Name n = new Name (LastName,FirstName);

      //Create address object
      String street = IO.getString("Please type your address: ");
      String city = IO.getString("Please type your city: ");
      String state = IO.getString("Please type your state: ");
      String zipcode = IO.getString("Please type your zipcode: ");
      Address addr = new Address (street,city,state,zipcode);

      //Create customer object
      String accno = IO.getString("Please enter the account number: ");
      Customer c = new Customer(n,addr,accno);
            //Create bankaccount object 
     double amt = IO.getDouble("Please type the opening account balance: ");
      BankAccount b = new BankAccount(c, amt);
      db.add(b);
      break;


      case 2:

      // Delete an account / copy account info to deleted database
       String key = IO.getString("Enter account number to delete: ");
           db.search(key); 
         if (db.inlist())
      {
            deleted.add(db.remove(db.getindex()));
      } else 
      {
        IO.notFound();
      }
      break;


      case 3:

      // withdraw from an account
        key = IO.getString("Enter account number to withdraw from: ");
        db.search(key);
       if (db.inlist())
      {
         double amount = IO.getDouble("Enter an amount to withdraw: ");
         db.getaccount().withdraw(amount);
         JOptionPane.showMessageDialog(null, "Current account balance is: "
                                        +db.getaccount().getbalance());
      } else 
         {
             IO.notFound();
         }
      break;  

      case 4:

      // Deposit to an account
          key = IO.getString("Enter account number to deposit to: ");
        db.search(key);
       if (db.inlist())
      {
         double amount = IO.getDouble("Enter an amount to deposit: ");
         db.getaccount().deposit(amount);
         JOptionPane.showMessageDialog(null, "Current account balance is: "
                                        +db.getaccount().getbalance());
      } else 
         {
             IO.notFound();
         }
      break;  

      case 5:
      // Display all current accounts
      if(db.list.isEmpty())
      {
        String s = "The list is empty";
        JTextArea text = new JTextArea(s, 6, 20);
        JScrollPane pane = new JScrollPane(text);
        JOptionPane.showMessageDialog(null, pane,
                    "Current Customers", JOptionPane.INFORMATION_MESSAGE);
      }

      for (int i = 0; i < db.list.size(); i++)
      {
       // JOptionPane.showMessageDialog(null, " "+db.list.size()); 
        String s = "These exists in the list: ";
        JTextArea text = new JTextArea(s, 6, 20);
        JScrollPane pane = new JScrollPane(text);
        JOptionPane.showMessageDialog(null, pane,
                    "Current Customers List", JOptionPane.INFORMATION_MESSAGE);
      }
      break;

      case 6:
      // Display all deleted accounts    in scroll pane like above
      {

      }

      case 7:
      // Display single account 
       key = IO.getString("Enter account number show: ");
       db.search(key);
       if (db.inlist())
      {
        JOptionPane.showMessageDialog(null, "Account number is: "
               +db.getaccount().getcustomer().getAccountNumber()+" Balance is: "
               +db.getaccount().balance);
      } else 
         {
             IO.notFound();
         }
      break;  

      case 8:

      // exit program
          done=true;
          break;

     default:
     JOptionPane.showMessageDialog(null, "Invalid choice, please choose again ", 
                                    "ERROR",JOptionPane.ERROR_MESSAGE);
        }
       }           
      }
      }

类

package bankaccount;

public class BankAccount 
{
Customer cust;
double balance;

BankAccount (Customer c,double b)     
   {
        cust = c;
     balance = b;
   }

 void deposit (double amt)
   {
     balance = balance + amt;
   }

 void withdraw (double amt)
   {
     balance = balance - amt;
   }

 double getbalance ()
   {
    return balance;
   }

 Customer getcustomer ()
   {
    return cust;
   }
    }

＆安培;

package bankaccount;

public class Customer 
{
 Name name;
 Address addr;
 String accno;

 Customer (Name n, Address addy, String acc)
 {
     name = n;
     addr = addy;
     accno = acc;
 }

 Name getname()
 {
     return name;
 }

 Address getAddress()
 {
     return addr;
 }

 String getAccountNumber()
 {
     return accno;
 }

 void changeAccountNumber(String acc)
 {
     accno = acc;
 }
 }

＆安培;

package bankaccount;

import java.util.ArrayList;

public class Database 
{
    int index;
    boolean found;
    ArrayList<BankAccount> list;
    BankAccount acc;

Database()
{
 list = new ArrayList<BankAccount>();
}

void add(BankAccount b)
{
   list.add(b);
}

BankAccount remove (int i)
{
    return list.remove(i);
}

 BankAccount getaccount()
{
    return acc;
}

ArrayList getlist()
{
    return list;
}

int getindex()
{
    return index;
}

boolean inlist()
{
    return found;
}

void search (String key)
{
    found = false;
    int i = 0;
    //int.length = list.size();

    while (i < list.size() && !found)
    { BankAccount b = list.get(i);
       if (key.equals(b.getcustomer().accno))
  {
  acc = b; found = true; index = i;
  }
else
  {
  i++;
  }
    }
}
}

＆安培;

package bankaccount;

public class Address 
{
 String street;
 String city;
 String state;
 String zipcode;     

  Address (String str, String cty, String st, String zip)
 {
     street = str;
     city = cty;
     state = st;
     zipcode = zip;
 }

 static String getstreet(String street)
 {
     return street;
 }

 public String getcity()
 {
     return city;
 } 

 public String getstate()
 {
     return state;
 }

 public String getzip()
 {
     return zipcode;
 }
}

＆安培;

package bankaccount;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import javax.swing.JOptionPane;

public class IO 
{       
        DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        Calendar cal = Calendar.getInstance();

     static double getDouble(String s)
     {
          return Double.parseDouble(getString(s));  
     }
     static int getInt(String s)
     {
          return Integer.parseInt(getString(s));    
     }
     static String getString(String s)
     {
          return JOptionPane.showInputDialog(s);
     }
     static void notFound() //Display not found
     {
        JOptionPane.showMessageDialog(null, "Account has not been found, "
                                            + "please try again");
     }      

     void date()
     {
         JOptionPane.showMessageDialog(null, "Current date is: ")+dateFormat.format(cal.getTime());
     }
}

Answer 1

您可以使用java.util.Calendar课程来处理日期。您也可以查看java.util.Date，但不推荐使用许多Date方法，不应使用。

public class Main {
    public static void main(String [] args){
        System.out.println(Calendar.getInstance().getTime());
    }
}

Java Date方法？类？ joptionpane /输出/显示数据库arraylist中的对象？

1 个答案: