2021/9/25

韩顺平 零基础30天学会Java

p307-p343

对象的多态：对象的编译类型和运算类型不一致

多态的向上转型：父类的引用指向子类的对象

向下转型：子类类型 引用名=（子类类型）父类引用

instanceof：对象的运行类型是否为xx类型或其子类型

java的动态绑定机制

多态数组

多态参数

equals方法

hashcode方法

toString方法

finalize方法

断点调试：运行类型

零钱通项目：使用java开发零钱通项目，可以完成收益入账、消费、查看明细、退出系统等功能

化繁为简

1.完成显示菜单

2.完成零钱通明细

3.完成收益入账

4.消费

5.退出

6.代码改进

7.改进（oop）面向对象

面向过程

public class SmallChange {
    public static void main(String[] args) {
        //1.显示菜单
        boolean loop = true;
        Scanner scanner = new Scanner(System.in);
        String key = "";
        //2.零钱通明细
        String details = "------------零钱通明细------------";
        //3.收益入账
        double money = 0;
        double balance = 0;
        Date date = null;
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm");
        //4.消费
        String note = "";
        //5.退出
        do {
            System.out.println("============零钱通菜单============");
            System.out.println("\t\t\t1.零钱通明细");
            System.out.println("\t\t\t2.收益入账");
            System.out.println("\t\t\t3.消费");
            System.out.println("\t\t\t4.退   出");
            System.out.println("请输入(1-4):");
            key = scanner.next();
            //switch语句
            switch (key) {
                case "1":
                    System.out.println(details);
                    break;
                case "2":
                    System.out.println("收益入账金额：");
                    money = scanner.nextDouble();
                    if (money <= 0) {
                        System.out.println("收益入账金额 需要 大于 0");
                        break;
                    }
                    balance += money;
                    date = new Date();
                    details += "\n收益入账\t\t+" + money + "\t" + sdf.format(date) + "\t" + balance;
                    break;
                case "3":
                    System.out.println("消费金额：");
                    money = scanner.nextDouble();
                    if (money <= 0 || money > balance) {
                        System.out.println("你的消费金额 应该在 0-" + balance);
                        break;
                    }
                    System.out.println("消费说明：");
                    note = scanner.next();
                    balance -= money;
                    date = new Date();
                    details += "\n" + note + "\t\t-" + money + "\t" + sdf.format(date) + "\t" + balance;
                    break;
                case "4":
                    String choice = "";
                    while (true) {
                        System.out.println("你确定要输出吗？y/n");
                        choice = scanner.next();
                        if ("y".equals(choice) || "n".equals(choice)) {
                            break;
                        }
                    }
                    if (choice.equals("y")) {
                        loop = false;
                    }
                    break;
                default:
                    System.out.println("选择有误，请重新选择");
            }
        } while (loop);
        System.out.println("-----退出了零钱通系统----");

    }
}

面向对象

public class SmallChangeOop {
    //1.显示菜单

    boolean loop = true;
    Scanner scanner = new Scanner(System.in);
    String key = "";
    //2.零钱通明细

    String details = "------------零钱通明细------------";
    //3.收益入账

    double money = 0;
    double balance = 0;
    Date date = null;
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm");
    //4.消费

    String note = "";

    //5.退出

    public void mainMenu() {
        System.out.println("显示零钱通菜单--");
        do {
            System.out.println("============零钱通菜单============");
            System.out.println("\t\t\t1.零钱通明细");
            System.out.println("\t\t\t2.收益入账");
            System.out.println("\t\t\t3.消费");
            System.out.println("\t\t\t4.退   出");
            System.out.println("请输入(1-4):");
            key = scanner.next();
            //switch语句
            switch (key) {
                case "1":
                   this.detail();
                    break;
                case "2":
                    this.income();
                    break;
                case "3":
                    this.pay();
                    break;
                case "4":
                    this.exit();
                    break;
                default:
                    System.out.println("选择有误，请重新选择");
            }
        } while (loop);
    }

    public void detail() {
        System.out.println(details);
    }

    public void income() {
        System.out.println("收益入账金额：");
        money = scanner.nextDouble();
        if (money <= 0) {
            System.out.println("收益入账金额 需要 大于 0");
            return;
        }
        balance += money;
        date = new Date();
        details += "\n收益入账\t\t+" + money + "\t" + sdf.format(date) + "\t" + balance;
    }

    public void pay() {
        System.out.println("消费金额：");
        money = scanner.nextDouble();
        if (money <= 0 || money > balance) {
            System.out.println("你的消费金额 应该在 0-" + balance);
            return;
        }
        System.out.println("消费说明：");
        note = scanner.next();
        balance -= money;
        date = new Date();
        details += "\n" + note + "\t\t-" + money + "\t" + sdf.format(date) + "\t" + balance;

    }

    public void exit() {
        String choice = "";
        while (true) {
            System.out.println("你确定要输出吗？y/n");
            choice = scanner.next();
            if ("y".equals(choice) || "n".equals(choice)) {
                break;
            }
        }
        if (choice.equals("y")) {
            loop = false;
        }
    }

test测试

public class Test {
    public static void main(String[] args){
        new SmallChangeOop().mainMenu();
    }

}