Java日期方法？类？joptionpane/从数据库输出/显示arraylist中的对象？

需要案例5和7的帮助

5显示所有对象和相关变量=（日期/账户#/名称在1行+地址在下四行+余额在最后一行

我不知道如何嵌套方法来执行上述操作/格式化输出

这看起来应该是这样的，但一直给我java语言空指针异常

  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;

&

&

&

---

您可以使用

java.util.Calendar

类来处理日期。 您还可以查看

java.util.Date

，但许多日期方法都已弃用，不应使用

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

---

非常感谢！这解决了我的日期问题。关于如何循环数据库中的所有对象并让它们返回，有什么建议吗？代码位于我的循环的顶部-如果您能帮助的话，我很感激=）

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;
   }
    }

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;
 }
 }   

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++;
  }
    }
}
}

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;
 }
}

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());
     }
}

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