在案例 5 和 7 方面需要一些帮助。
5 显示所有对象和相关变量 =（第一行的日期/帐户#/名称 + 下四行的地址 + 最后一行的余额。
我不知道如何嵌套执行上述操作/格式化输出的方法。
这看起来应该但一直给我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。在此先感谢，下面的完整代码
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);
}
}
}
}
班级
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());
}
}