【Java 基础实验_Bank项目_06】单例模式(Static Bank) , 查询异常输出

基于上一个实验Banking_5 ,代码先全部复制过来.

笔记心得:

1.SavingAccount() 需要两种构造方法,接受单个参数和两个的
2.Account 有两个类型 SavingAccount 和 CheckingAccount ,每个人都有两个或一个 ,
 setAccount(Account account,int id) ,id=1 表示设置前者, id=2表示设置后者.
3.在 public class CustomerReport{}中 ,首先调用static Bank : Bank bank=Bank.getBank();
然后遍历其中元素, 可能存在只有一个账户,所以需要特判一下:
 if(customer.getSavingAccount()!=null) 和if(customer.getCheckingAccount()!=null)  ,解决这个空内存 的异常!

实验要求:

　　

实验目的：
单例模式。 

提示：
 1． 修改 Bank 类，创建名为 getBanking 的公有静态方法，它返回一个 Bank 类的实例。  2． 单个的实例应是静态属性，且为私有。同样，Bank 构造器也应该是私有的 

创建 CustomerReport 类 

1.在前面的银行项目练习中，“客户报告”嵌入在 TestBanking 应用程序的 main 方法中。在这个练习中，改代码被放在，banking.reports 包的
 CustomerReport 类中。您的任务是修改这个类，使其使用单一银行对象。  

2． 查找标注为注释块/***  ***/的代码行.修改该行以检索单子银行对象。 

文件工程组织: (基于上一个实验Banking_5 ,代码 先 全部复制过来,然后再具体改改.)

具体代码:

　　Bank.java   (构造器方法私有化,private static Bank bank=new Bank();)

package Banking_6;
    //要求使bank实现单例模式
public class Bank {
    private Customer[] customers ;   //用于存放客户
    private int numberofCustomers; //用于记录Customer的个数

    private Bank(){    ///构造器方法私有化
        numberofCustomers=0;
        customers = new Customer[100];  ///这里记得要初始化!不然要发生java.lang.NullPointerException
    }
    private static Bank bank=new Bank();
    public static Bank getBank(){
        return bank;
    }
    public void addCustomer(String f,String l){
        int i= this.numberofCustomers;
        customers[i]=new Customer(f,l);//新建一个构造对象
        this.numberofCustomers++;
    }
    public int getNumOfCustomers() {
        return numberofCustomers;
    }
    public Customer getCustomer(int index) {
        return customers[index];
    }
}

　　CustomerReport.java  (打印全部Bank的信息 )

package Banking_6;
        //遍历银行里的所有账户,进行汇报
public class CustomerReport {
    Bank bank=Bank.getBank();
    public void generateReport(){
        System.out.println("=======================================");
        System.out.println("          "+"CUSTOMERS REPORT");
        System.out.println("=======================================");
        int num=bank.getNumOfCustomers();
        Customer customer;
        Account Savingaccount,Checkingaccount;
        for(int i=0;i<num;i++){
            customer=bank.getCustomer(i);
            Savingaccount = customer.getSavingAccount();
            Checkingaccount=customer.getCheckingAccount();
            //输出所有存款信息
            System.out.println("Customer: "+customer.getFirstName()+" "+customer.getLastName());
            if(customer.getSavingAccount()!=null)
                System.out.println("SavingAccount: current balance is $"+customer.getSavingAccount().getBalance());
            if(customer.getCheckingAccount()!=null)
                System.out.println("CheckingAccount: current balance is $"+customer.getCheckingAccount().getBalance());
            System.out.println();
        }
    }

}

　　TestBank.java

package TestBanks;
import Banking_6.*;
public class TestBanking_6 {

    public static void main(String[] args) {
        Bank  bank = Bank.getBank();
        Customer customer;
        CustomerReport report = new CustomerReport();

        // Create several customers and their accounts
        bank.addCustomer("Jane", "Simms");
        customer = bank.getCustomer(0);
        customer.setAccount(new SavingAccount(500.00, 0.05),1);
        customer.setAccount(new CheckingAccount(200.00, 400.00),2);

        bank.addCustomer("Owen", "Bryant");
        customer = bank.getCustomer(1);
        customer.setAccount(new CheckingAccount(200.00),2);

        bank.addCustomer("Tim", "Soley");
        customer = bank.getCustomer(2);
        customer.setAccount(new SavingAccount(1500.00, 0.05),1);
        customer.setAccount(new CheckingAccount(200.00),2);

        bank.addCustomer("Maria", "Soley");
        customer = bank.getCustomer(3);
        // Maria and Tim have a shared checking account
        customer.setAccount(bank.getCustomer(2).getCheckingAccount(),1);
        customer.setAccount(new SavingAccount(150.00, 0.05),2);

        // Generate a report
        report.generateReport();
    }
}

　　Account.java

package Banking_6;
public class Account {

    protected double balance=0;//余额  ,uml前该变量是 '-'
    public Account(double init_balance){
        balance=init_balance;
    }
    public double getBalance() {
        return balance;
    }
    public void setBalance(double b){this.balance=b;}
    //存钱

    public boolean deposit(double amt){
        this.balance+=amt;return true;
    }
    //取钱
    public Boolean withdraw(double amt) {
        if(amt>this.balance)
            return false;
        else{
            this.balance-=amt;
            return true;
        }
    }
}

　　TestBanking_6.java  (测试类) 

 package TestBanks;
 import Banking_6.*;
 public class TestBanking_6 {

     public static void main(String[] args) {
         Bank  bank = Bank.getBank();
         Customer customer;
         CustomerReport report = new CustomerReport();

         // Create several customers and their accounts
         bank.addCustomer("Jane", "Simms");
         customer = bank.getCustomer(0);
         customer.setAccount(new SavingAccount(500.00, 0.05),1);
         customer.setAccount(new CheckingAccount(200.00, 400.00),2);

         bank.addCustomer("Owen", "Bryant");
         customer = bank.getCustomer(1);
         customer.setAccount(new CheckingAccount(200.00),2);

         bank.addCustomer("Tim", "Soley");
         customer = bank.getCustomer(2);
         customer.setAccount(new SavingAccount(1500.00, 0.05),1);
         customer.setAccount(new CheckingAccount(200.00),2);

         bank.addCustomer("Maria", "Soley");
         customer = bank.getCustomer(3);
         // Maria and Tim have a shared checking account
         customer.setAccount(bank.getCustomer(2).getCheckingAccount(),1);
         customer.setAccount(new SavingAccount(150.00, 0.05),2);

         // Generate a report
         report.generateReport();
     }
 }

输出结果:

=======================================
          CUSTOMERS REPORT
=======================================
Customer: Jane Simms
SavingAccount: current balance is $500.0
CheckingAccount: current balance is $200.0

Customer: Owen Bryant
CheckingAccount: current balance is $200.0

Customer: Tim Soley
SavingAccount: current balance is $1500.0
CheckingAccount: current balance is $200.0

Customer: Maria Soley
SavingAccount: current balance is $200.0
CheckingAccount: current balance is $150.0