21. java面向对象 - JavaBean

2023-07-24 20:36:28

一、定义

JavaBean是一种Java语言写成的可重用组件，所谓JavaBean是指符合如下要求的java类：①类是公共的 ②有一个无参的公共构造器 ③有属性，且有对应的get、set方法。用户可以使用JavaBean将功能、处理、值、数据库访问和其他任何可以用Java代码创造的对象进行打包，并且其他的开发者可以通过内部的JSP页面、Servlet、其他JavaBean、applet程序或应用来使用这些对象。用户可以认为JavaBean提供了一种随时随地的复制粘贴的功能，而不要关心任何改变。

二、this关键字

this可以修饰属性、方法、构造器
- this理解为当前对象
- 在类方法中，用"this.属性"或"this.方法"是调用对象的属性或方法，一般我们都省this

public class Person {
    private String name;
    private int age;

    //构造器
    public Person(){
        this.eat();
    }

    public Person(String name){
        this.name = name;
    }

    public Person(String name, int age){
        this.name = name;
        this.age = age;
    }


    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
    //如果不加this，则设置是就是空字符串，因为name就是形参就近原则
    //加上后，就可区分this.name是属性；后面name是形参
    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void eat(){
        System.out.println("people eat fruit");
        this.study();
    }

    public void study(){
        System.out.println("pepole study english");
    }
}

class PersonTest{
    public static void main(String[] args) {
        Person p1 = new Person();
        p1.eat();
    }
}

this调构造器
- 我们在构造器中，可以显示使用"this(形参列表)"方式调用指定本类中指定其他构造器
- 构造器中，不能使用"this(形参列表)"方式调用自己
- 如果一个类中有n个构造器，最多有n-1个调用，不能成环
- 构造器中只能声明一个"this(形参列表)"

public class Person {
    private String name;
    private int age;

    //构造器;若没创建对象都要去实现一段代码为了减少冗余，使用this调构造器
    public Person(){
        System.out.println("person 需要创建很多...,现行创建");
    }

    public Person(String name){
        // 调用空参构造器
        this();
        this.name = name;
    }

    public Person(String name, int age){
        // 调用带参构造器，此构造起中有name参数，就不需要自己创建了
        this(name);
        //this.name = name;
        this.age = age;
    }

    // 封装性体现
    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void eat(){
        System.out.println("people eat fruit");
        this.study();
    }

    public void study(){
        System.out.println("pepole study english");
    }
}

class PersonTest{
    public static void main(String[] args) {
        Person p1 = new Person("tom", 18);
        System.out.println(p1.getAge());
    }
}

三、实例

1. account

public class Account {
    /*
     * id:账号
     * balance:余额
     * annualInterestRate:年利率
     * */
    private int id;
    private double balance;
    private double annualInterestRate;

    //构造器
    public Account(int id, double balance, double annualInterestRate) {
        this.id = id;
        this.balance = balance;
        this.annualInterestRate = annualInterestRate;
    }

    //get和set方法
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public double getBalance() {
        return balance;
    }

    public void setBalance(double balance) {
        this.balance = balance;
    }

    public double getAnnualInterestRate() {
        return annualInterestRate;
    }

    public void setAnnualInterestRate(double annualInterestRate) {
        this.annualInterestRate = annualInterestRate;
    }

    //取钱
    public void withdraw(double amount) {
        //余额不足提示
        if (balance < amount) {
            System.out.println("sorry, Insufficient balance");
            return;
        }
        balance -= amount;
        System.out.println("Successfully withdraw" + " " + amount + " yuan!");
    }

    //存钱
    public void deposit(double amount) {
        if (amount > 0) {
            balance += amount;
            System.out.println("Successfully deposited" + " " + amount + " yuan!");
        }
    }
}

2. customer

public class Customer {
    private String firstName;
    private String lastName;
    //对象属性
    private Account account;

    public Customer(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public Account getAccount() {
        return account;
    }

    public void setAccount(Account account) {
        this.account = account;
    }
}

3. customerTest

public class CustomerTest {
    public static void main(String[] args) {
        /*
        * 一个用户Jane Smith，账号1001，余额2000，利率1.23%
        * */
        Customer customerObj = new Customer("Jone","Smith");
        Account accountObj = new Account(1001, 2000, 0.0123);
        //在银行开个户，设置id=1001，金额2000
        customerObj.setAccount(accountObj);
        //先通过用户获取账户，存100元，取960元
        customerObj.getAccount().deposit(100);
        customerObj.getAccount().withdraw(960);
        customerObj.getAccount().withdraw(2000);
    }
}

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