Xin mọi người xem hộ em với không hiểu sao lại có lỗi này ạ 
Em có 2 class
package samsung.java.week2.bank;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Scanner;
public class SavingAccount {
// tien goc
private double principalAmount;
// ngay bat dau gui
private Date depositDate;
//thoi gian bat dau rut
private long withdrawal;
// lai suat theo %
private double interestRate;
// so tai khoan
private int accountNumber;
// ten tai khoan
private String accountName;
Scanner enter = new Scanner(System.in);
public int getAccountNumber() {
return accountNumber;
}
public void setAccountNumber(int accountNumber) {
this.accountNumber = accountNumber;
}
public String getAccountName() {
return accountName;
}
public void setAccountName(String accountName) {
this.accountName = accountName;
}
public double getPrincipalAmount() {
return principalAmount;
}
public void setPrincipalAmount(double principalAmount) {
this.principalAmount = principalAmount;
}
public Date getDepositDate() {
return depositDate;
}
public void setDepositDate(Date depositDate) {
this.depositDate = depositDate;
}
public double getInterestRate() {
return interestRate;
}
public void setInterestRate(double interestRate) {
this.interestRate = interestRate;
}
public long getWithdrawal() {
return withdrawal;
}
public void setWithdrawal(long withdrawal) {
this.withdrawal = withdrawal;
}
// khoi tao mac dinh khong tham so
public SavingAccount() {
setAccountNumber(01234567);
setAccountName("abcd");
}
// calculate interest
// Tinh tien lai
public double calculateInterest() {
double interest = getPrincipalAmount() * getInterestRate() * ((getWithdrawal() - getDepositDate().getTime()) / 86400000);
return interest;
}
// phuong thuc rut tien lai
public void withdrawalInterest() {
System.out.println("Interest :" + calculateInterest());
// get current date time with Date()
Date date = new Date();
setDepositDate(date);
}
// rut tien lai va mot phan tien goc (interest and partial withdrawals
// principals)
public void interestAndPWP() {
System.out.println("Enter principal amount need withdraw : ");
double principalWithdraw = enter.nextDouble();
do {
if (principalWithdraw <= 0) {
System.out.println("principalWithdraw > 0. Please enter again.");
} else {
setPrincipalAmount(getPrincipalAmount() - principalWithdraw);
System.out.println("principal Withdraw : " + principalWithdraw);
withdrawalInterest();
}
} while (principalWithdraw <= 0);
}
//nhap ngay rut
public void withdrawalDate(){
System.out.print("Plase enter withdrawal date (dd/MM/yyyy) :");
String expectedPattern = "dd/MM/yyyy";
SimpleDateFormat formatter = new SimpleDateFormat(expectedPattern);
try
{
// (2) give the formatter a String that matches the
//SimpleDateFormat pattern
String userInput = enter.nextLine();
Date date = formatter.parse(userInput);
setWithdrawal(date.getTime());
}catch (Exception e){
// execution will come here if the String that is given
// does not match the expected format.
e.printStackTrace();
}
}
// gui them tien vao tien goc
public void sendMoreMoney() {
System.out.println("Please enter send more money : ");
double sendMoreMoney = enter.nextDouble();
if (getPrincipalAmount() != 0) {
do {
if (sendMoreMoney <= 0) {
System.out.println("principalWithdraw > 0. Please enter again.");
} else {
setPrincipalAmount(getPrincipalAmount() + sendMoreMoney);
withdrawalInterest();
withdrawalDate();
}
} while (sendMoreMoney <= 0);
}
if (getPrincipalAmount() == 0) {
do {
if (sendMoreMoney <= 0) {
System.out.println("principalWithdraw > 0. Please enter again.");
} else {
setPrincipalAmount(getPrincipalAmount() + sendMoreMoney);
withdrawalDate();
}
} while (sendMoreMoney <= 0);
}
}
// rut tat
public void withdrawalAll() {
System.out.println("You withdrawal principal amount : " + getPrincipalAmount());
withdrawalInterest();
setPrincipalAmount(0);
}
}
và một class
package samsung.java.week2.bank;
import java.io.IOException;
import java.util.Scanner;
public class Communication {
private static SavingAccount[] account = new SavingAccount[50];
public static int i = 0;
// chuc nang tao acc va nhap lai suat
public static void appendNewAccount() {
Scanner enter = new Scanner(System.in);
System.out.println("Please, enter new account number (0-9): ");
account[i].setAccountNumber(enter.nextInt());
if (compare(i) == 1) {
System.out.println("account number already exists ");
}
if (compare(i) != 1) {
System.out.println("Please, enter new account name : ");
account[i].setAccountName(enter.nextLine());
System.out.println("Please, enter interest rate (%) : ");
account[i].setInterestRate(enter.nextDouble());
i++;
}
if (compare(i) == 0) {
System.out.println("Please, enter new account name : ");
account[i].setAccountName(enter.nextLine());
System.out.println("Please, enter interest rate (%) : ");
account[i].setInterestRate(enter.nextDouble());
i++;
}
}
// so sanh account trung so account number tra ve 1
public static int compare(int i) {
int test = 0;
if (i == 0) {
test = 0;
}
if (i != 0) {
for (int j = (i - 1); j >= 0; j--) {
if ((account[i].getAccountNumber()) != (account[j].getAccountNumber())) {
test = 0;
} else {
test = 1;
// quit for
break;
}
}
}
return test;
}
// test = 50 la khong co tai khoan. de la 50 de khi tra ve i chi co the <50
// search account number
public static int searchAccountNumber(int searchAccountNumber) {
int test = 50;
for (int j = 0; j <= i; j++) {
if (searchAccountNumber == account[i].getAccountNumber()) {
test = i;
// quit for
break;
} else {
test = 50;
}
}
return test;
}
// chuc nang rut tien lai
public static void functionWithdrawalInterest() {
Scanner enter = new Scanner(System.in);
System.out.println("Please enter account number : ");
int searchAccountNumber = enter.nextInt();
if (searchAccountNumber(searchAccountNumber) != 50) {
// gan k = so nay de the hien cac hoat dong duoi day la cua mot doi
// tuong k
// neu khong khi ta lam account[i] se la i cua tai khoan vua lap
int k = searchAccountNumber(searchAccountNumber);
account[k].withdrawalInterest();
} else {
System.out.println("account number not have!");
}
}
// chuc nang rut goc mot phan
public static void functionInterestAndPWP() {
Scanner enter = new Scanner(System.in);
System.out.println("Please enter account number : ");
int searchAccountNumber = enter.nextInt();
if (searchAccountNumber(searchAccountNumber) != 50) {
// gan k = so nay de the hien cac hoat dong duoi day la cua mot doi
// tuong k
// neu khong khi ta lam account[i] se la i cua tai khoan vua lap
int k = searchAccountNumber(searchAccountNumber);
account[k].interestAndPWP();
} else {
System.out.println("account number not have!");
}
}
// chuc nang tat toan
public static void functionWithdrawalAll() {
Scanner enter = new Scanner(System.in);
System.out.println("Please enter account number : ");
int searchAccountNumber = enter.nextInt();
if (searchAccountNumber(searchAccountNumber) != 50) {
// gan k = so nay de the hien cac hoat dong duoi day la cua mot doi
// tuong k
// neu khong khi ta lam account[i] se la i cua tai khoan vua lap
int k = searchAccountNumber(searchAccountNumber);
account[k].withdrawalAll();
} else {
System.out.println("account number not have!");
}
}
// chuc nang gui tien
public static void functionSendMoreMoney() {
Scanner enter = new Scanner(System.in);
System.out.println("Please enter account number : ");
int searchAccountNumber = enter.nextInt();
if (searchAccountNumber(searchAccountNumber) != 50) {
// gan k = so nay de the hien cac hoat dong duoi day la cua mot doi
// tuong k
// neu khong khi ta lam account[i] se la i cua tai khoan vua lap
int k = searchAccountNumber(searchAccountNumber);
account[k].sendMoreMoney();
} else {
System.out.println("account number not have!");
}
}
// chuc nang xem thong tin
public static void showAccount() {
Scanner enter = new Scanner(System.in);
System.out.println("Please enter account number : ");
int searchAccountNumber = enter.nextInt();
if (searchAccountNumber(searchAccountNumber) != 50) {
// gan k = so nay de the hien cac hoat dong duoi day la cua mot doi
// tuong k.
// neu khong khi ta lam account[i] se la i cua tai khoan vua lap
int k = searchAccountNumber(searchAccountNumber);
System.out.println("Account Number :" + account[k].getAccountNumber());
System.out.println("Account Name :" + account[k].getAccountName());
System.out.println("Principal amount :" + account[k].getPrincipalAmount());
System.out.println("Interest :" + account[k].calculateInterest());
} else {
System.out.println("account number not have!");
}
}
// show menu
public static void showMenu() {
System.out.println(" Bank Management System");
System.out.println("------------------------------");
System.out.println("1. Append new account");
System.out.println("2. Withdraw interest");
System.out.println("3. Partialy withdraw ");
System.out.println("4. Totally withdraw");
System.out.println("5. Deposit");
System.out.println("6. Display information");
System.out.println("Your choice (1-6, other to quit): ");
}
public static void main(String[] args) {
showMenu();
Scanner enter = new Scanner(System.in);
String choice = enter.nextLine();
int next = 0;
do {
switch (choice) {
case "1":
appendNewAccount();
break;
case "2":
functionWithdrawalInterest();
break;
case "3":
functionInterestAndPWP();
break;
case "4":
functionWithdrawalAll();
break;
case "5":
functionSendMoreMoney();
break;
case "6":
showAccount();
break;
default:
System.out.println("you are quit!");
}
// Enter "Enter" show again the menu.
System.out.println("Press Enter to continue...");
try {
next = System.in.read();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
String trash = enter.nextLine();
} while (next == 13);
}
}
Khi em chạy chọn 1 và nhập vào một số vd: 123 thì nó báo ngoại lệ
Bank Management System
------------------------------
1. Append new account
2. Withdraw interest
3. Partialy withdraw
4. Totally withdraw
5. Deposit
6. Display information
Your choice (1-6, other to quit):
1
Please, enter new account number (0-9):
123
Exception in thread "main" java.lang.NullPointerException
at samsung.java.week2.bank.Communication.appendNewAccount(Communication.java:15)
at samsung.java.week2.bank.Communication.main(Communication.java:176)
Em nghĩ nó là cái này lỗi: account[i].setAccountNumber(enter.nextInt()); nhưng không hiểu sai ở đâu.
Xin mọi người mách em xử lý với ạ.
Em xin cảm ơn.
83% thành viên diễn đàn không hỏi bài tập, còn bạn thì sao?