⭐构建框架

首先我们必须很清楚最后实现出的结果是什么样的

有管理员和普通用户两个选择。普通用户和管理员显示的菜单是不一样的。

先新建一个Main类，里面实现菜单，调用方法，程序的主逻辑。

然后新建一个book包。新建user包，里面新建User类(父类)，AdminUser类(子类)，NormalUser类(子类)，AdminUser类和NormalUser类这两个类都要继承User这个父类。
用户要有姓名属性。

public  class User {
    protected String name;
    public User(String name){
        this.name=name;
    }
    }

public class AdminUser extends User{
public AdminUser(String name) {
        super(name);//先帮助父类构造
        }

public class NormalUser extends User{
public NormalUser(String name) {
        super(name);//先帮助父类构造
        }

构造一个book对象，有name,author,price,type,是否被借出这5个属性。

public class Book {
    private String name;
    private String author;
    private int price;
    private String type;
    private boolean isBorrowed;
    }

public Book(String name, String author, int price, String type) {
        this.name = name;
        this.author = author;
        this.price = price;
        this.type = type;
    }
    这里不初始化isBorrowed，默认是false，未被借出

因为这些属性都是private修饰，所以调用get,set方法

public String getName() {
        return name;
    }

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

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public int getPrice() {
        return price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

为了以后方便打印书，再重写一个toString()

public String toString() {
        return "Book{" +
                "name='" + name + '\'' +
                ", author='" + author + '\'' +
                ", price=" + price +
                ", type='" + type + '\'' +", "+
                ((isBorrowed==true)?"该书已借出":"该书未借出")+
                '}';
    }

现在需要一个书架放很多书，创建一个数组作为书架，以后的显示书，删除书，新增书都是对这个数组做操作。

在book包里面新建BookList书架，假设默认能放10本书，还要知道当前书架有几本书。

public class BookList {
    private Book[] books=new Book[10];
    private int usedSize;//存储当前书的个数

前面显示图书默认显示3本书，那么就要在程序运行的时候往书架里存三本书。
可以在调用BookList的构造方法时，存3本书。

public BookList(){
        books[0]=new Book("三国演义","罗贯中",89,"小说");
        books[1]=new Book("西游记","吴承恩",78,"小说");
        books[2]=new Book("红楼梦","曹雪芹",49,"小说");
        this.usedSize=3;
    }

接下来我们需要写查找，新增，删除，显示，借阅，归还，退出这些操作，这些是一种标准/规范，我们可以把它们写成接口。

在src底下新建operations包，包里新建AddOperation(新增图书)等等操作。

public class AddOperation {
    public void work(BookList bookList){
        System.out.println("新增图书!");
        }
        }

public class FindOperation {
    public void work(BookList bookList){
        System.out.println("查找图书!");
        }
        }

可以发现新增图书和查找图书里面的work方法都是构成重写的，所以可以在operations包里新建一个IOperation接口

public interface IOperation {
    void work(BookList bookList);
}

public class AddOperation implements IOperation {
public class FindOperation implements IOperation{

让AddOperation，FindOperation实现IOperation接口。

这里接口的意义：为了之后实现向上转型，动态绑定，多态

public class DelOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("删除图书!");
        }
        }

显示，借阅，归还，退出这些操作和上面写的类似

🎈Main类

public class Main {
public static void main(String[] args) {
        BookList bookList=new BookList();
        User user=login();

准备3本书，用户登录

选择1或0就知道是管理员还是普通用户，然后导出不同的菜单
(多态)

public static User login(){
        System.out.println("请输入你的姓名：");
        Scanner scanner=new Scanner(System.in);
        String userName=scanner.nextLine();
        System.out.println("请输入你的身份：1-》管理员，0-》普通用户");
        int choice=scanner.nextInt();
        if(choice==1){
            return new AdminUser(userName);
        }else{
            return new NormalUser(userName);
        }
    }

这里返回值实现了向上转型

User user=login();

AdminUser和NormalUser都重写menu()。user引用的对象不一样，user.menu()打印的菜单不一样。

//AdminUser的menu():
public class AdminUser extends User{
public void menu(){
        System.out.println("**************************************");
        System.out.println("hello "+name+" 欢迎来到图书小练习！ ");
        System.out.println("1.查找图书");
        System.out.println("2.新增图书");
        System.out.println("3.删除图书");
        System.out.println("4.显示图书");
        System.out.println("0.退出系统");
        System.out.println("**************************************");
    }

//NormalUser的menu()
public class NormalUser extends User {
public void menu(){
        System.out.println("**************************************");
        System.out.println("hello "+name+" 欢迎来到图书小练习！ ");
        System.out.println("1.查找图书");
        System.out.println("2.借阅图书");
        System.out.println("3.归还图书");
        System.out.println("0.退出系统");
        System.out.println("**************************************");
        }

 user.menu();

直接这么写会报错，因为父类User没有menu()。
所以要在父类重写一个menu()。

public abstract class User {
public abstract void menu();
//不写方法体可以写成abstract，然后父类User就是抽象类

然后是输入你的操作，接收输入的数字。
所以menu()的返回值改成int。

public int menu(){
System.out.println("请输入你的操作：");
        Scanner scanner=new Scanner(System.in);
        int choice =scanner.nextInt();
        return choice;
    }

那么怎样通过输入的数字调用相对应的用户的接口？

//在User类里定义一个数组
public abstract class User {
    protected IOperation[] iOperations;

//在 AdminUser类里初始化IOperation数组
public class AdminUser extends User{
    public AdminUser(String name) {
        super(name);
        this.iOperations=new IOperation[]{
                new ExitOperation(),
                new FindOperation(),
                new AddOperation(),
                new DelOperation(),
                new DisplayOperation()
        };
    }

public class NormalUser extends User {

    public NormalUser(String name) {
        super(name);
        this.iOperations=new IOperation[]{
                new ExitOperation(),
                new FindOperation(),
                new BorrowOperation(),
                new ReturnOperation()
        };
    }

user引用的是哪个对象就初始化它的IOperation数组。

接下来需要写一个操作接口数组的方法，写在User类里

public abstract class User {
   public void doOperation(int choice, BookList bookList){
        iOperations[choice].work(bookList);
    }
}

public class Main {
public static void main(String[] args) {
        BookList bookList=new BookList();
        User user=login();
        while(true) {//循环输入操作，直到0退出
            int choice = user.menu();
            user.doOperation(choice, bookList);
        }
        }
}

就main函数来完整分析一遍思路，第一步初始化书架，书架里预存3本书，然后登录，输入姓名，输入身份(管理员/普通用户)，new一个用户对象，初始化相对应的接口数组，返回值是父类User，向上转型，调用menu(),多态。菜单再输入操作数字，调用user的doOperation(choice, bookList)，找到对应用户的接口数组的choice下标，new一个操作，调用操作里的方法。

接下来具体实现查找，新增，删除，显示，借阅，归还，退出这些操作。

⭐对图书的操作

🎈查找图书

根据书名查找，找到之后打印书的所有属性。

遍历books数组比较书名，数组长度是usedSize(private)。

public int getUsedSize() {
        return usedSize;
    }

    public void setUsedSize(int usedSize) {
        this.usedSize = usedSize;
    }

然后遍历过程如何通过i找到books数组对应的书，books数组(private)。数组是私有所以要调用getPos()

public class BookList {
public Book getPos(int pos){
        return books[pos];
        }
    }
 

public class FindOperation implements IOperation{
    public void work(BookList bookList){
        System.out.println("查找图书!");
        System.out.println("请输入你要查找的图书的名字：");
        Scanner scanner=new Scanner(System.in);
        String name=scanner.nextLine();
        int currentSize= bookList.getUsedSize();
        for (int i = 0; i < currentSize; i++) {
            Book book=bookList.getPos(i);
            if(name.equals(book.getName())){//比较书名
                System.out.println("找到了这本书！");
                System.out.println(book);
                return ;
            }
        }
        System.out.println("没有这本书！");
    }
}

🎈新增图书

public class AddOperation implements IOperation {
    public void work(BookList bookList){
        System.out.println("新增图书!");
        System.out.println("请输入你要新增的图书的名字：");
        Scanner scanner=new Scanner(System.in);
        String name=scanner.nextLine();//读取回车
        System.out.println("请输入你要新增的图书的作者：");
        String author=scanner.nextLine();
        System.out.println("请输入你要新增的图书的价格：");
        int price=scanner.nextInt();
        scanner.nextLine();
        System.out.println("请输入你要新增的图书的类型：");
        String type=scanner.nextLine();
        Book book=new Book(name,author,price,type);

现在需要把这本书放到书架上。
再books数组usedSize下标处放一本书，然后usedSize++。

public class BookList {
public void setBooks(Book book,int pos){
        books[pos]=book;
    }
    public void setUsedSize(int usedSize) {
        this.usedSize = usedSize;
    }
    }

public class AddOperation implements IOperation {
    public void work(BookList bookList){
            int currentSize= bookList.getUsedSize();
            bookList.setBooks(book,currentSize);
        bookList.setUsedSize(currentSize+1);
        System.out.println("新增成功");
        }
        }

🎈显示图书

public class DisplayOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("显示所有图书！");
        int currentSize= bookList.getUsedSize();
        for (int i = 0; i < currentSize; i++) {
            Book book=bookList.getPos(i);
            System.out.println(book);
        }
    }
}

🎈退出系统

public class ExitOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("退出系统！");
        System.exit(0);
    }
}

🎈删除图书

public class DelOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("删除图书!");
        System.out.println("请输入你要删除的图书：");
        Scanner scanner=new Scanner(System.in);
        String name=scanner.nextLine();
        int index=-1;
        int currentSize= bookList.getUsedSize();
        for (int i = 0; i < currentSize; i++) {
            Book book=bookList.getPos(i);
            if(name.equals(book.getName())){
                index=i;
                break;
            }
        }
        if(index==-1){
            System.out.println("没有你要删除的书！");
            return;
        }

如果找到了要删除的书，删除的方法是后面覆盖前面，最后usedSize–。

for (int i = index; i <currentSize-1; i++) {
            Book book=bookList.getPos(i+1);
            bookList.setBooks(book,i);
        }

        bookList.setBooks(null,currentSize-1);
        bookList.setUsedSize(currentSize-1);
        System.out.println("删除成功！");

每次删除都要置空，在Java中一个对象只有没人引用的情况下才会被回收。

🎈借阅图书

public class BorrowOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("借阅书籍！");
        System.out.println("请输入你要借阅的图书的名字：");
        Scanner scanner=new Scanner(System.in);
        String name=scanner.nextLine();
        int currentSize= bookList.getUsedSize();
        for (int i = 0; i < currentSize; i++) {
            Book book=bookList.getPos(i);
            if(name.equals(book.getName())){
                if(book.isBorrowed()){
                    System.out.println("该书已经被借出！");
                }else{
                    book.setBorrowed(true);
                    System.out.println("借阅图书成功！");
                }
                return;
            }
        }
        System.out.println("没有你要借阅的书！");
    }
}

🎈归还图书

public class ReturnOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("归还图书！");
        System.out.println("请输入你要归还的图书的名字：");
        Scanner scanner=new Scanner(System.in);
        String name=scanner.nextLine();
        int currentSize= bookList.getUsedSize();
        for (int i = 0; i < currentSize; i++) {
            Book book=bookList.getPos(i);
            if(name.equals(book.getName())){
                book.setBorrowed(false);
                System.out.println("归还图书成功！");
                return;
            }
        }
        System.out.println("没有你要归还的书！");
    }
}

⭐完整代码

🎈book包

🔥Book

package book;

public class Book {
    private String name;
    private String author;
    private int price;
    private String type;
    private boolean isBorrowed;

    public Book(String name, String author, int price, String type) {
        this.name = name;
        this.author = author;
        this.price = price;
        this.type = type;
    }

    public String getName() {
        return name;
    }

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

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public int getPrice() {
        return price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public boolean isBorrowed() {
        return isBorrowed;
    }

    public void setBorrowed(boolean borrowed) {
        isBorrowed = borrowed;
    }

    @Override
    public String toString() {
        return "Book{" +
                "name='" + name + '\'' +
                ", author='" + author + '\'' +
                ", price=" + price +
                ", type='" + type + '\'' +", "+
                ((isBorrowed==true)?"该书已借出":"该书未借出")+
                '}';
    }
}

🔥BookList

package operations;

import book.Book;
import book.BookList;

import java.util.Scanner;

public class ReturnOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("归还图书！");
        System.out.println("请输入你要归还的图书的名字：");
        Scanner scanner=new Scanner(System.in);
        String name=scanner.nextLine();
        int currentSize= bookList.getUsedSize();
        for (int i = 0; i < currentSize; i++) {
            Book book=bookList.getPos(i);
            if(name.equals(book.getName())){
                book.setBorrowed(false);
                System.out.println("归还图书成功！");
                return;
            }
        }
        System.out.println("没有你要归还的书！");
    }
}

🎈operations包

🔥AddOperation

package operations;

import book.Book;
import book.BookList;
import com.sun.deploy.panel.IProperty;

import java.util.Scanner;

public class AddOperation implements IOperation {
    public void work(BookList bookList){
        System.out.println("新增图书!");
        System.out.println("请输入你要新增的图书的名字：");
        Scanner scanner=new Scanner(System.in);
        String name=scanner.nextLine();
        System.out.println("请输入你要新增的图书的作者：");
        String author=scanner.nextLine();
        System.out.println("请输入你要新增的图书的价格：");
        int price=scanner.nextInt();
        scanner.nextLine();
        System.out.println("请输入你要新增的图书的类型：");
        String type=scanner.nextLine();
        int currentSize= bookList.getUsedSize();
        Book book=new Book(name,author,price,type);
        bookList.setBooks(book,currentSize);
        bookList.setUsedSize(currentSize+1);
        System.out.println("新增成功");
    }
}

🔥BorrowOperation

package operations;

import book.Book;
import book.BookList;

import java.util.Scanner;

public class BorrowOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("借阅书籍！");
        System.out.println("请输入你要借阅的图书的名字：");
        Scanner scanner=new Scanner(System.in);
        String name=scanner.nextLine();
        int currentSize= bookList.getUsedSize();
        for (int i = 0; i < currentSize; i++) {
            Book book=bookList.getPos(i);
            if(name.equals(book.getName())){
                if(book.isBorrowed()){
                    System.out.println("该书已经被借出！");
                }else{
                    book.setBorrowed(true);
                    System.out.println("借阅图书成功！");
                }
                return;
            }
        }
        System.out.println("没有你要借阅的书！");
    }
}

🔥DelOperation

package operations;

import book.Book;
import book.BookList;

import java.util.Scanner;

public class DelOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("删除图书!");
        System.out.println("请输入你要删除的图书：");
        Scanner scanner=new Scanner(System.in);
        String name=scanner.nextLine();
        int index=-1;
        int currentSize= bookList.getUsedSize();
        for (int i = 0; i < currentSize; i++) {
            Book book=bookList.getPos(i);
            if(name.equals(book.getName())){
                index=i;
                break;
            }
        }
        if(index==-1){
            System.out.println("没有你要删除的书！");
            return;
        }
        for (int i = index; i <currentSize-1; i++) {
            Book book=bookList.getPos(i+1);
            bookList.setBooks(book,i);
        }
        bookList.setBooks(null,currentSize-1);
        bookList.setUsedSize(currentSize-1);
        System.out.println("删除成功！");
    }
}

🔥DisplayOperation

package operations;

import book.Book;
import book.BookList;

public class DisplayOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("显示所有图书！");
        int currentSize= bookList.getUsedSize();
        for (int i = 0; i < currentSize; i++) {
            Book book=bookList.getPos(i);
            System.out.println(book);
        }
    }
}

🔥ExitOperation

package operations;

import book.BookList;

public class ExitOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("退出系统！");
        System.exit(0);
    }
}

🔥FindOperation

package operations;

import book.Book;
import book.BookList;

import java.util.Scanner;

public class FindOperation implements IOperation{
    public void work(BookList bookList){
        System.out.println("查找图书!");
        System.out.println("请输入你要查找的图书的名字：");
        Scanner scanner=new Scanner(System.in);
        String name=scanner.nextLine();
        int currentSize= bookList.getUsedSize();
        for (int i = 0; i < currentSize; i++) {
            Book book=bookList.getPos(i);
            if(name.equals(book.getName())){
                System.out.println("找到了这本书！");
                System.out.println(book);
                return ;
            }
        }
        System.out.println("没有这本书！");
    }
}

🔥IOperation

package operations;

import book.BookList;

public interface IOperation {
    void work(BookList bookList);
}

🔥ReturnOperation

package operations;

import book.Book;
import book.BookList;

import java.util.Scanner;

public class ReturnOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("归还图书！");
        System.out.println("请输入你要归还的图书的名字：");
        Scanner scanner=new Scanner(System.in);
        String name=scanner.nextLine();
        int currentSize= bookList.getUsedSize();
        for (int i = 0; i < currentSize; i++) {
            Book book=bookList.getPos(i);
            if(name.equals(book.getName())){
                book.setBorrowed(false);
                System.out.println("归还图书成功！");
                return;
            }
        }
        System.out.println("没有你要归还的书！");
    }
}

🎈user包

🔥Adminuser

package user;

import operations.*;

import java.util.Scanner;

public class AdminUser extends User{

    public AdminUser(String name) {
        super(name);
        this.iOperations=new IOperation[]{
                new ExitOperation(),
                new FindOperation(),
                new AddOperation(),
                new DelOperation(),
                new DisplayOperation()
        };
    }
    public int menu(){
        System.out.println("**************************************");
        System.out.println("hello "+name+" 欢迎来到图书小练习！ ");
        System.out.println("1.查找图书");
        System.out.println("2.新增图书");
        System.out.println("3.删除图书");
        System.out.println("4.显示图书");
        System.out.println("0.退出系统");
        System.out.println("**************************************");
        System.out.println("请输入你的操作：");
        Scanner scanner=new Scanner(System.in);
        int choice =scanner.nextInt();
        return choice;
    }
}

🔥Normaluser

package user;

import operations.*;

import java.util.Scanner;

public class NormalUser extends User {

    public NormalUser(String name) {
        super(name);
        this.iOperations=new IOperation[]{
                new ExitOperation(),
                new FindOperation(),
                new BorrowOperation(),
                new ReturnOperation()
        };
    }
    public int menu(){
        System.out.println("**************************************");
        System.out.println("hello "+name+" 欢迎来到图书小练习！ ");
        System.out.println("1.查找图书");
        System.out.println("2.借阅图书");
        System.out.println("3.归还图书");
        System.out.println("0.退出系统");
        System.out.println("**************************************");
        System.out.println("请输入你的操作：");
        Scanner scanner=new Scanner(System.in);
        int choice =scanner.nextInt();
        return choice;
    }
}

🔥User

package user;

import book.BookList;
import operations.IOperation;

public abstract class User {
    protected String name;
    protected IOperation[] iOperations;
    public User(String name){
        this.name=name;
    }
    public abstract int menu();
    public void doOperation(int choice, BookList bookList){
        iOperations[choice].work(bookList);
    }
}

🎈Main类

import book.BookList;
import user.AdminUser;
import user.NormalUser;
import user.User;

import java.util.Scanner;

public class Main {
    public static User login(){
        System.out.println("请输入你的姓名：");
        Scanner scanner=new Scanner(System.in);
        String userName=scanner.nextLine();
        System.out.println("请输入你的身份：1-》管理员，0-》普通用户");
        int choice=scanner.nextInt();
        if(choice==1){
            return new AdminUser(userName);
        }else{
            return new NormalUser(userName);
        }
    }

    public static void main(String[] args) {
        BookList bookList=new BookList();
        User user=login();
        while(true) {
            int choice = user.menu();
            user.doOperation(choice, bookList);
        }
    }
}