Java面向对象-- “ 图书管理系统 ”_设计一个图书管理系统。系统具有以下几个功能: 查询全部书籍、添加书籍、借阅书籍

运行环境：IDEA

1 需求

1、实现根据不同身份登陆；
2、用户身份：管理员、普通用户
管理员实现功能：增加图书、删除图书、查看所有书籍的列表、查阅某个书籍的信息、退出程序；
普通用户：借阅书籍、归还书籍、查阅某个书籍的信息、退出程序。

2 代码实现

  我们找到这个系统的一个个的对象，逐步来实现。

2.1 Book、BookList

  图书管理系统，首先最重要的就是书。
  在创建类里面的属性时，明确封装是面向对象的重要核心之一，设计这个 book 类的时候，book 类的属性，尽可能封装起来，用 private，使其他的程序猿能不用理解具体细节，降低使用成本。

package Test1_28_LibraryManagementSystem;

public class Book {
    private String name;
    private String author;
    private double price;
    private String type;
    // 默认是false ，但是显示的写出来可读性更好
    private boolean isBorrowed = false;

    // 每本书的名字、价格、作者、类型，可能不同
    // 使用构造方法，构造的时候以传入参数的形式，确定具体的值
    // 构造实例时，显示的创建相关参数，来传入相关信息
    public Book(String name, String author, double price, String type) {
        this.name = name;
        this.author = author;
        this.price = price;
        this.type = type;
    }

// 重写 toString 方法才能在打印书籍信息时，以字符串的样子打印出来
    @Override
    public String toString() {
        return "Book{" +
                "name='" + name + '\'' +
                ", author='" + author + '\'' +
                ", price=" + price +
                ", type='" + type + '\'' +
                ", isBorrowed=" + isBorrowed +
                '}';
    }
// getter / setter 和封装是相悖的 ，但是封装并不是百分百藏起来，完全包裹起来调用者不好使用。
    public String getName() {
        return name;
    }

    public boolean isBorrowed() {
        return isBorrowed;
    }

    public void setBorrowed(boolean borrowed) {
        isBorrowed = borrowed;
    }
}
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为了记录所有书籍信息，创建一个书籍列表

package Test1_28_LibraryManagementSystem;

public class BookList {
    Book books[] = new Book[100];
    int size = 0;

// 这样就写死了这些书，创建实例它们就存在
    public BookList() {
        books[0] = new Book("西游记","吴承恩",50.0,"古典名著");
        books[1] = new Book("水浒传","施耐庵",50.0,"古典名著");
        books[2] = new Book("三国演义","罗贯中",50.0,"古典名著");
        books[3] = new Book("红楼梦","曹雪芹",50.0,"古典名著");
        size = 4;
    }

// 通过 getter和setter 来获取和修改书籍列表 
    public Book getBook(int index) {
        return books[index];
    }

    public void setBook(int index,Book book) {
        books[index] = book;
    }

    public int getSize() {
        return size;
    }

    public void setSize(int size) {
        this.size = size;
    }
}
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2.2 使用者

1、管理员

package Test1_28_LibraryManagementSystem;
import Test1_28_LibraryManagementSystem.IOperation.*;
import java.util.Scanner;

public class Admin extends User{

    public Admin(String name) {
        this.name = name;
        this.operations = new IOperation[]{
                new AddOperation(),
                new DelOperation(),
                new DisplayBookList(),
                new FindOperation(),
                new ExitOperation()
        };
    }

    @Override
    public int menu() {
        System.out.println("*********************");
        System.out.println(" 1、新增书籍 ");
        System.out.println(" 2、删除书籍 ");
        System.out.println(" 3、展示书籍列表 ");
        System.out.println(" 4、查找某本书籍 ");
        System.out.println(" 5、退出系统 ");
        System.out.println("*********************");
        System.out.println("请输入您的选择：");
        Scanner scanner = new Scanner(System.in);
        int choice = scanner.nextInt();
        return choice;
    }
}
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2、普通用户

package Test1_28_LibraryManagementSystem;
import Test1_28_LibraryManagementSystem.IOperation.*;
import java.util.Scanner;

public class NormalUser extends User{

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

    public int menu(){
        System.out.println("*********************");
        System.out.println(" 1、借阅书籍 ");
        System.out.println(" 2、归还书籍 ");
        System.out.println(" 3、查找某本书籍 ");
        System.out.println(" 4、退出系统 ");
        System.out.println("*********************");
        System.out.println("请输入您的选择：");
        Scanner scanner = new Scanner(System.in);
        int choice = scanner.nextInt();
        return choice;
    }
}
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3、用户
创建抽象类 User ，这样在使用时，调用者可以不关注是管理员还是普通用户，管理员和用户继承 User 。

package Test1_28_LibraryManagementSystem;
import Test1_28_LibraryManagementSystem.IOperation.IOperation;

abstract public class User {
    protected String name;
    protected IOperation[] operations;
    public abstract int menu();

    public void doOperation(int choice,BookList bookList){
        this.operations[choice - 1].work(bookList);
    }

}
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2.3 操作

  设计用户操作，每种类都可以设置成一个类，每个操作类中都有一个 work 方法，public 修饰、返回void、传入BookList。因为他们有共性，就可以把共性信息提取出来，做成一个接口。（消除重复 并且 在不相关的类之间建立联系）
  当前 IOperation 这个接口其实就是把所有的用户操作给统一规范起来了，什么样的类作为一种用户的操作？只要实现了这个接口，就可以作为用户的操作。
1、接口

package Test1_28_LibraryManagementSystem.IOperation;

import Test1_28_LibraryManagementSystem.BookList;

public interface IOperation {
    void work(BookList bookList);
}
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注意：
如果多各类之间，公共的部分只有方法的话，此时使用接口；
如果多个类之间，公共的部分不光有方法还有属性，此时使用继承（普通父类 / 抽象父类）。

2.3.1 管理员操作

1、新增书籍

package Test1_28_LibraryManagementSystem.IOperation;
import Test1_28_LibraryManagementSystem.Book;
import Test1_28_LibraryManagementSystem.BookList;
import java.util.Scanner;

public class AddOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("新增图书 >> ");
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要新增书籍的书名：");
        String name = scanner.next();
        System.out.println("请输入书籍作者的名字：");
        String author = scanner.next();
        System.out.println("请输入书籍的价格：");
        Double price = scanner.nextDouble();
        System.out.println("请输入书籍的类型：");
        String type = scanner.next();
        Book newBook = new Book(name,author,price,type);
        bookList.setBook(bookList.getSize(),newBook);
        bookList.setSize(bookList.getSize() + 1);
    }
}
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2、删除书籍

package Test1_28_LibraryManagementSystem.IOperation;
import Test1_28_LibraryManagementSystem.BookList;
import java.util.Scanner;
import java.util.jar.JarOutputStream;

public class DelOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("删除书籍 >> ");
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要删除书籍的书名：");
        String name = scanner.next();
        int i = 0;
        for (; i < bookList.getSize(); i++) {
            if(name.equals(bookList.getBook(i).getName())) {
                if(i == bookList.getSize() - 1) {
                    bookList.setSize(bookList.getSize() - 1);
                    System.out.println("删除成功");
                    return;
                }
                bookList.setBook(i,bookList.getBook(bookList.getSize() - 1));
                bookList.setSize(bookList.getSize() - 1);
                System.out.println("删除成功");
                return;
            }
        }
        if (i >= bookList.getSize() - 1) {
            System.out.println("未找到《" + name + "》，删除失败");
        }
    }
}
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3、展示书籍列表

package Test1_28_LibraryManagementSystem.IOperation;
import Test1_28_LibraryManagementSystem.BookList;

public class DisplayBookList implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("展示书籍列表 >> ");
        for (int i = 0; i < bookList.getSize(); i++) {
            System.out.println(bookList.getBook(i));
        }
    }
}
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4、查找某本书籍信息

package Test1_28_LibraryManagementSystem.IOperation;
import Test1_28_LibraryManagementSystem.BookList;
import java.util.Scanner;

public class FindOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("查找某本书籍信息 >> ");
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要查找书籍的书名：");
        String name = scanner.next();
        int i = 0;
        for (; i < bookList.getSize(); i++) {
            if(bookList.getBook(i).getName().contains(name)) {
                System.out.println(bookList.getBook(i));
                System.out.println("查找成功");
                return;
            }
        }
        if(i >= bookList.getSize() - 1) {
            System.out.println("未找到《" + name + "》，查找失败");
        }
    }
}
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5、退出系统

package Test1_28_LibraryManagementSystem.IOperation;
import Test1_28_LibraryManagementSystem.BookList;

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

1、借阅书籍

package Test1_28_LibraryManagementSystem.IOperation;
import Test1_28_LibraryManagementSystem.BookList;
import java.util.Scanner;

public class BorrowOperation implements IOperation {
    @Override
    public void work(BookList bookList) {
        System.out.println("借阅书籍 >> ");
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要借阅书籍的书名：");
        String name = scanner.next();
        int i = 0;
        for (; i < bookList.getSize(); i++) {
            if(name.equals(bookList.getBook(i).getName())) {
                if(!bookList.getBook(i).isBorrowed()) {
                    bookList.getBook(i).setBorrowed(true);
                    System.out.println("借阅成功");
                    return;
                }
                System.out.println("《" + name + "》已被借阅，借阅失败");
                return;
            }
        }
        if(i >= bookList.getSize() - 1) {
            System.out.println("未找到 《" + name + "》，借阅失败");
        }
    }
}
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2、归还书籍

package Test1_28_LibraryManagementSystem.IOperation;
import Test1_28_LibraryManagementSystem.BookList;
import java.util.Scanner;

public class ReturnOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("归还书籍 >> ");
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要归还书籍的书名：");
        String name = scanner.next();
        for (int i = 0; i < bookList.getSize(); i++) {
            if(name.equals(bookList.getBook(i).getName())) {
                if(!bookList.getBook(i).isBorrowed()) {
                    System.out.println("《" + name + "》未被借阅，归还失败");
                    return;
                }
                bookList.getBook(i).setBorrowed(false);
                System.out.println("归还成功");
                return;
            }
        }
        System.out.println("未找到《" + name + "》，归还失败");
    }
}
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3、查找某本书的信息（ 与管理员的查找相同 ）

package Test1_28_LibraryManagementSystem.IOperation;
import Test1_28_LibraryManagementSystem.BookList;
import java.util.Scanner;

public class FindOperation implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("查找某本书籍信息 >> ");
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要查找书籍的书名：");
        String name = scanner.next();
        int i = 0;
        for (; i < bookList.getSize(); i++) {
            if(bookList.getBook(i).getName().contains(name)) {
                System.out.println(bookList.getBook(i));
                System.out.println("查找成功");
                return;
            }
        }
        if(i >= bookList.getSize() - 1) {
            System.out.println("未找到《" + name + "》，查找失败");
        }
    }
}
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4、退出系统（ 与管理员的查找相同 ）

package Test1_28_LibraryManagementSystem.IOperation;
import Test1_28_LibraryManagementSystem.BookList;

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

package Test1_28_LibraryManagementSystem;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        BookList bookList = new BookList();
        // 向上转型，login返回管理员或普通用户
        User user = login();
        while (true) {
        //多态
            int choice = user.menu();
            user.doOperation(choice,bookList);
        }

    }

    private static User login() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入您的姓名：");
        String name = scanner.next();
        System.out.println(name + "欢迎使用！");
        System.out.println("请选择您的身份：");
        System.out.println(" 0、管理员  1、用户 ");
        int who = scanner.nextInt();
        if(who == 0){
            return new Admin(name);
        }
        return new NormalUser(name);
    }
}
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