【Java 实习】Day 02

逃离我推掉我的手 2023-01-01 02:50 163阅读 0赞

### 实例：银行 ###

> 案例：银行卡账户类方法  
> 存钱取钱转账方法模拟场景：
> 
> > 张三使用建设银行卡存入了3000  
> > 李四使用农业银行卡存入5000  
> > 王五使用交通银行卡存入了4000  
> > 李四转账2000给张三  
> > 张三转账1000给王五
> 
> 体现出继承关系和多态

1.  定义一个抽象类Bank作为所有银行类的父类
2.  定义三个银行类继承Bank
3.  Bank中定义存钱、取钱和转账的方法
4.  由于Bank无法获取具体银行名称，因此在三个银行子类中需要重写存钱和取钱方法
5.  定义测试类BankTest

*  用到的快捷键

<table> 
 <thead> 
  <tr> 
   <th>快捷键</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Alt+Insert</td> 
   <td>快速定义构造函数、set函数和get函数</td> 
  </tr> 
  <tr> 
   <td>Alt+Enter</td> 
   <td>补全变量定义</td> 
  </tr> 
  <tr> 
   <td><code>\**</code>+Enter</td> 
   <td>注释</td> 
  </tr> 
 </tbody> 
</table>

//Bank.java
    package pers.syx.beans;
    
    public abstract class Bank {
        
        private String bankName;        //银行名
        private double accountBalance;  //账户余额
        private String accountName;     //账户名
    
    
        /**
         * 存钱方法
         * @param money
         * @param accountName
         */
        public void saveMoney(double money, String accountName){
        
            this.setAccountName(accountName);
    
            double accountBalance = this.getAccountBalance();
            accountBalance += money;
            this.setAccountBalance(accountBalance);
        }
    
        /**
         * 取钱方法
         * @param money
         * @param accountName
         */
        public void takeMoney(double money, String accountName){
        
            this.setAccountName(accountName);
    
            double accountBalance = this.getAccountBalance();
            accountBalance -= money;
            this.setAccountBalance(accountBalance);
        }
    
        /**
         * 转账方法：将钱从 bank1 转到 bank2
         * @param money
         * @param bank1
         * @param bank2
         */
        public void transferMoney(double money, Bank bank1, Bank bank2){
        
            double accountBalance = bank1.getAccountBalance();
            accountBalance -= money;
            bank1.setAccountBalance(accountBalance);
    
            accountBalance = bank2.getAccountBalance();
            accountBalance += money;
            bank2.setAccountBalance(accountBalance);
    
            System.out.println(bank1.getAccountName()+"转账"+money+"给"+bank2.getAccountName());
        }
    
        public Bank(String bankName, double accountBalance, String accountName) {
        
            this.bankName = bankName;
            this.accountBalance = accountBalance;
            this.accountName = accountName;
        }
    
        public Bank() {
        
        }
    
        public String getBankName() {
        
            return bankName;
        }
    
        public void setBankName(String bankName) {
        
            this.bankName = bankName;
        }
    
        public double getAccountBalance() {
        
            return accountBalance;
        }
    
        public void setAccountBalance(double accountBalance) {
        
            this.accountBalance = accountBalance;
        }
    
        public String getAccountName() {
        
            return accountName;
        }
    
        public void setAccountName(String accountName) {
        
            this.accountName = accountName;
        }
    }

//CCB.java
    package pers.syx.beans;
    
    public class CCB extends Bank{
        
        public static final String BANK_NAME = "建设银行";
    
        /**
         * 重写父类存钱方法
         * @param money
         * @param accountName
         */
        @Override
        public void saveMoney(double money, String accountName) {
        
            super.saveMoney(money, accountName);
            this.setBankName(BANK_NAME);
    
            System.out.println(this.getAccountName()+"在"+this.getBankName()+"中存入了"+money);
        }
    
        /**
         * 重写父类取钱方法
         * @param money
         * @param accountName
         */
        @Override
        public void takeMoney(double money, String accountName) {
        
            super.takeMoney(money, accountName);
            this.setBankName(BANK_NAME);
    
            System.out.println(this.getAccountName()+"从"+this.getBankName()+"中取出了"+money);
        }
    }

//ABC.java
    package pers.syx.beans;
    
    public class ABC extends Bank{
        
        public static final String BANK_NAME = "农业银行";
    
        /**
         * 重写父类存钱方法
         * @param money
         * @param accountName
         */
        @Override
        public void saveMoney(double money, String accountName) {
        
            super.saveMoney(money, accountName);
            this.setBankName(BANK_NAME);
    
            System.out.println(this.getAccountName()+"在"+this.getBankName()+"中存入了"+money);
        }
    
        /**
         * 重写父类取钱方法
         * @param money
         * @param accountName
         */
        @Override
        public void takeMoney(double money, String accountName) {
        
            super.takeMoney(money, accountName);
            this.setBankName(BANK_NAME);
    
            System.out.println(this.getAccountName()+"从"+this.getBankName()+"中取出了"+money);
        }
    }

//BC.java
    package pers.syx.beans;
    
    public class BC extends Bank{
        
        public static final String BANK_NAME = "交通银行";
    
        /**
         * 重写父类存钱方法
         * @param money
         * @param accountName
         */
        @Override
        public void saveMoney(double money, String accountName) {
        
            super.saveMoney(money, accountName);
            this.setBankName(BANK_NAME);
    
            System.out.println(this.getAccountName()+"在"+this.getBankName()+"中存入了"+money);
        }
    
        /**
         * 重写父类取钱方法
         * @param money
         * @param accountName
         */
        @Override
        public void takeMoney(double money, String accountName) {
        
            super.takeMoney(money, accountName);
            this.setBankName(BANK_NAME);
    
            System.out.println(this.getAccountName()+"从"+this.getBankName()+"中取出了"+money);
        }
    }

//BankTest.java
    package pers.syx.beans;
    
    public class BankTest {
        
        public static void main(String[] args) {
        
            Bank bank1 = new CCB();
            bank1.saveMoney(3000,"张三");
            Bank bank2 = new ABC();
            bank2.saveMoney(5000,"李四");
            Bank bank3 =new BC();
            bank3.saveMoney(4000,"王五");
    
            bank2.transferMoney(2000,bank2,bank1);
            bank1.transferMoney(1000,bank1,bank3);
        }
    }

--------------------

抽象类的简单介绍

*  抽象类不能实例化对象，即抽象类不可以有具体的实例
 *  抽象方法没有方法体，且只能存在于抽象类中。没有方法体的方法一定为抽象方法
 *  抽象类中可以有普通方法
 *  抽象类只能被继承，子类必须重写父类中的抽象方法
 *  一个类没有抽象方法，也可以定义为抽象类，但依然不能实例化对象。这个抽象类作为顶层父类，体现继承关系，但是定义为抽象类意义不大
 *  private和abstract冲突，final和abstract冲突，因为private和final类不能被继承