新手在线等解决，急！Exception in thread "main" java.lang.NullPointerException

[ssc85]

新手在线等，请问该如何修改？

package banking;

public class Account {
	protected double balance;

	public Account(double balance) {
		super();
		this.balance = balance;
	}

	public double getBalance() {
		return balance;
	}

	public void setBalance(double balance) {
		this.balance = balance;
	}
	
	public boolean deposit(double amt) {
		balance+=amt;
		return true;
	}
	public boolean withdraw(double amt) {
		if(amt<=balance) {
			balance -= amt;
		}else {
			return false;
		}
		return true;
	
	}
 	
	

}


package banking;

public class SavingAccount extends Account {
	private double interestRate;

	public SavingAccount(double balance, double interestRate) {
		super(balance);
		this.interestRate = interestRate;
	}

	public double getInterestRate() {
		return interestRate;
	}
	

}


package banking;

public class CheckingAccount extends Account {
	private double overdraftProtection;

	public CheckingAccount(double balance) {
		super(balance);
	}

	public CheckingAccount(double balance, double overdraftProtection) {
		super(balance);
		this.overdraftProtection = overdraftProtection;
	}
	
	public boolean withdraw(double amt) {
		if(amt<=balance) {
			balance -= amt;
			return true;
		}else {
			if(overdraftProtection>= amt - balance) {
				overdraftProtection -= amt - balance;
				balance = 0;
			}else {
				return false;
			}
		}
		return true;
	}
	

}


package banking;

public class Customer {
	private String lastName;
	public String getLastName() {
		return lastName;
	}
	public String getFirstName() {
		return firstName;
	}


	private String firstName;
	Account[] accounts;
	 int numberOfAccounts;
	public Customer(String L,String F) {
	
		lastName = L;
		firstName =F;
	}
	public Customer() {
	
		accounts = new Account[2];
	}
	
	public void addAccount(Account account) {
		
		accounts[numberOfAccounts++]=account;
	}
	public Account getAccounts(int index) {
		return   accounts [index];
	}
	
	
	public int getNumberOfAccounts() {
		return numberOfAccounts;
	}
	

}


package banking;

public class Bank {
	private Customer[] customers;
	private int numberOfCustomers;
	public Bank() {
		customers = new Customer[5];
	}
	public Customer getCustomers(int index) {
		return customers[index];
	}
	public int getNumberOfCustomers() {
		return numberOfCustomers;
	}
	public void addCustomer(String L,String F) {
		Customer customer = new Customer(L,F);
		 customers[numberOfCustomers]=customer;
		 numberOfCustomers++;
	}
	
	

}



package banking;

public class TestBanking {
	public static void main(String[] args) {
		Bank bank = new Bank();
		Customer customer;
		
		
		
		
		bank.addCustomer("Jane", "Smith");
		customer = bank.getCustomers(0);
		customer.addAccount(new SavingAccount(500,0.05));
		customer.addAccount(new CheckingAccount(200,400));
		
		bank.addCustomer("oven", "Bryant");
		customer = bank.getCustomers(1);
		customer.addAccount(new CheckingAccount(200));
		
		bank.addCustomer("Tim", "Soley");
		customer=bank.getCustomers(2);
		customer.addAccount(new SavingAccount(1500,0.05));
		customer.addAccount(new CheckingAccount(200));
		
		bank.addCustomer("Maria", "Soley");
		customer = bank.getCustomers(3);
		customer.addAccount(bank.getCustomers(2).getAccounts(1));
		customer.addAccount(new SavingAccount(150,0.05));
		
		for(int i = 0;i<bank.getNumberOfCustomers();i++) {
			customer = bank.getCustomers(i);
			System.out.println();
			System.out.println("Customer "+customer.getLastName()+customer.getFirstName());
			
		}
		
		

		
		
	

		
	}

}

错误是Exception in thread "main" java.lang.NullPointerException
at banking.Customer.addAccount(Customer.java:28)
at banking.TestBanking.main(TestBanking.java:13)
不明白哪里错了，怎么修改？

[喵学长]

空指针异常你查看异常处的对象，很快就能发现问题

[ssc85]

那请问该如何修改啊，我还是个小萌新、、

[李德胜1995]

很明显accounts为null嘛。。。。

[无伤]

accounts 没有初始化，建议使用list代替数组。

[码农高射炮]

代码里有个地方有问题，Bank类定义的时候使用customer[]来保存客户信息，但是在addCustomer(String f,String l)中 你新定义了一个临时变量coustomer[]来保存添加的客户信息，最终在测试的时候你去取customer中信息，肯定是空的，也就是你添加的客户信息并没有保存在customer中，只是添加在一个临时变量cousomer里了，肯定访问不到。 把这段public void addCustomer(String f,String l) { Customer coustomer[]=new Customer[5]; coustomer[numberOfCustomers]=new Customer(f,l); numberOfCustomers++; }改为 public void addCustomer(String f,String l) { // Customer coustomer[]=new Customer[5]; customer[numberOfCustomers]=new Customer(f,l); numberOfCustomers++; }再试一下效果。

[踏实低调]

修改下边这个构造器： public Customer(String L,String F) { lastName = L; firstName =F; accounts = new Account[2]; //这句话添上就没问题了 } 原因简单地解释一下，因为你的Customer定义了两个构造器，上边这个是接受两个参数，另一个是默认的无参构造器，如下： public Customer() { accounts = new Account[2]; } 数组accounts的初始化放在了默认构造器中，但是你的main方法的代码只会调用接受两个参数的构造器。所以accounts并没有被初始化。

[自由自在_Yu]

引用 6 楼 aiyou_ 的回复:

修改下边这个构造器： public Customer(String L,String F) { lastName = L; firstName =F; accounts = new Account[2]; //这句话添上就没问题了 } 原因简单地解释一下，因为你的Customer定义了两个构造器，上边这个是接受两个参数，另一个是默认的无参构造器，如下： public Customer() { accounts = new Account[2]; } 数组accounts的初始化放在了默认构造器中，但是你的main方法的代码只会调用接受两个参数的构造器。所以accounts并没有被初始化。