運行環境：IDEA

1 需求

1、實作根據不同身份登陸；
2、用戶身份：管理員、普通用戶
管理員實作功能：增加圖書、洗掉圖書、查看所有書籍的串列、查閱某個書籍的資訊、退出程式；
普通用戶：借閱書籍、歸還書籍、查閱某個書籍的資訊、退出程式，

2 代碼實作

??我們找到這個系統的一個個的物件，逐步來實作，

2.1 Book、BookList

??圖書管理系統，首先最重要的就是書，
??在創建類里面的屬性時，明確封裝是面向物件的重要核心之一，設計這個 book 類的時候，book 類的屬性，盡可能封裝起來，用 private，使其他的程式猿能不用理解具體細節，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;
    // 默認是false ，但是顯示的寫出來可讀性更好
    private boolean isBorrowed = false;

    // 每本書的名字、價格、作者、型別，可能不同
    // 使用構造方法，構造的時候以傳入引數的形式，確定具體的值
    // 構造實體時，顯示的創建相關引數，來傳入相關資訊
    public Book(String name, String author, double price, String type) {
        this.name = name;
        this.author = author;
        this.price = price;
        this.type = type;
    }

// 重寫 toString 方法才能在列印書籍資訊時，以字串的樣子列印出來
    @Override
    public String toString() {
        return "Book{" +
                "name='" + name + '\'' +
                ", author='" + author + '\'' +
                ", price=" + price +
                ", type='" + type + '\'' +
                ", isBorrowed=" + isBorrowed +
                '}';
    }
// getter / setter 和封裝是相悖的 ，但是封裝并不是百分百藏起來，完全包裹起來呼叫者不好使用，
    public String getName() {
        return name;
    }

    public boolean isBorrowed() {
        return isBorrowed;
    }

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

為了記錄所有書籍資訊，創建一個書籍串列

package Test1_28_LibraryManagementSystem;

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

// 這樣就寫死了這些書，創建實體它們就存在
    public BookList() {
        books[0] = new Book("西游記","吳承恩",50.0,"古典名著");
        books[1] = new Book("水滸傳","施耐庵",50.0,"古典名著");
        books[2] = new Book("三國演義","羅貫中",50.0,"古典名著");
        books[3] = new Book("紅樓夢","曹雪芹",50.0,"古典名著");
        size = 4;
    }

// 通過 getter和setter 來獲取和修改書籍串列 
    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;
    }
}

2.2 使用者

1、管理員

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、新增書籍 ");
        System.out.println(" 2、洗掉書籍 ");
        System.out.println(" 3、展示書籍串列 ");
        System.out.println(" 4、查找某本書籍 ");
        System.out.println(" 5、退出系統 ");
        System.out.println("*********************");
        System.out.println("請輸入您的選擇：");
        Scanner scanner = new Scanner(System.in);
        int choice = scanner.nextInt();
        return choice;
    }
}

2、普通用戶

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、借閱書籍 ");
        System.out.println(" 2、歸還書籍 ");
        System.out.println(" 3、查找某本書籍 ");
        System.out.println(" 4、退出系統 ");
        System.out.println("*********************");
        System.out.println("請輸入您的選擇：");
        Scanner scanner = new Scanner(System.in);
        int choice = scanner.nextInt();
        return choice;
    }
}

3、用戶
創建抽象類 User ，這樣在使用時，呼叫者可以不關注是管理員還是普通用戶，管理員和用戶繼承 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);
    }

}

2.3 操作

??設計用戶操作，每種類都可以設定成一個類，每個操作類中都有一個 work 方法，public 修飾、回傳void、傳入BookList，因為他們有共性，就可以把共性資訊提取出來，做成一個介面，（消除重復并且在不相關的類之間建立聯系）
??當前 IOperation 這個介面其實就是把所有的用戶操作給統一規范起來了，什么樣的類作為一種用戶的操作？只要實作了這個介面，就可以作為用戶的操作，
1、介面

package Test1_28_LibraryManagementSystem.IOperation;

import Test1_28_LibraryManagementSystem.BookList;

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

注意：
如果多各類之間，公共的部分只有方法的話，此時使用介面；
如果多個類之間，公共的部分不光有方法還有屬性，此時使用繼承（普通父類 / 抽象父類），

2.3.1 管理員操作

1、新增書籍

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("新增圖書 >> ");
        Scanner scanner = new Scanner(System.in);
        System.out.println("請輸入要新增書籍的書名：");
        String name = scanner.next();
        System.out.println("請輸入書籍作者的名字：");
        String author = scanner.next();
        System.out.println("請輸入書籍的價格：");
        Double price = scanner.nextDouble();
        System.out.println("請輸入書籍的型別：");
        String type = scanner.next();
        Book newBook = new Book(name,author,price,type);
        bookList.setBook(bookList.getSize(),newBook);
        bookList.setSize(bookList.getSize() + 1);
    }
}

2、洗掉書籍

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("洗掉書籍 >> ");
        Scanner scanner = new Scanner(System.in);
        System.out.println("請輸入要洗掉書籍的書名：");
        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("洗掉成功");
                    return;
                }
                bookList.setBook(i,bookList.getBook(bookList.getSize() - 1));
                bookList.setSize(bookList.getSize() - 1);
                System.out.println("洗掉成功");
                return;
            }
        }
        if (i >= bookList.getSize() - 1) {
            System.out.println("未找到《" + name + "》，洗掉失敗");
        }
    }
}

3、展示書籍串列

package Test1_28_LibraryManagementSystem.IOperation;
import Test1_28_LibraryManagementSystem.BookList;

public class DisplayBookList implements IOperation{
    @Override
    public void work(BookList bookList) {
        System.out.println("展示書籍串列 >> ");
        for (int i = 0; i < bookList.getSize(); i++) {
            System.out.println(bookList.getBook(i));
        }
    }
}

4、查找某本書籍資訊

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("查找某本書籍資訊 >> ");
        Scanner scanner = new Scanner(System.in);
        System.out.println("請輸入要查找書籍的書名：");
        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 + "》，查找失敗");
        }
    }
}

5、退出系統

package Test1_28_LibraryManagementSystem.IOperation;
import Test1_28_LibraryManagementSystem.BookList;

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

2.3.2 用戶操作

1、借閱書籍

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("借閱書籍 >> ");
        Scanner scanner = new Scanner(System.in);
        System.out.println("請輸入要借閱書籍的書名：");
        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("借閱成功");
                    return;
                }
                System.out.println("《" + name + "》已被借閱，借閱失敗");
                return;
            }
        }
        if(i >= bookList.getSize() - 1) {
            System.out.println("未找到 《" + name + "》，借閱失敗");
        }
    }
}

2、歸還書籍

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("歸還書籍 >> ");
        Scanner scanner = new Scanner(System.in);
        System.out.println("請輸入要歸還書籍的書名：");
        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 + "》未被借閱，歸還失敗");
                    return;
                }
                bookList.getBook(i).setBorrowed(false);
                System.out.println("歸還成功");
                return;
            }
        }
        System.out.println("未找到《" + name + "》，歸還失敗");
    }
}

3、查找某本書的資訊（與管理員的查找相同）

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("查找某本書籍資訊 >> ");
        Scanner scanner = new Scanner(System.in);
        System.out.println("請輸入要查找書籍的書名：");
        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 + "》，查找失敗");
        }
    }
}

4、退出系統（與管理員的查找相同）

package Test1_28_LibraryManagementSystem.IOperation;
import Test1_28_LibraryManagementSystem.BookList;

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

2.4 呼叫

package Test1_28_LibraryManagementSystem;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        BookList bookList = new BookList();
        // 向上轉型，login回傳管理員或普通用戶
        User user = login();
        while (true) {
        //多型
            int choice = user.menu();
            user.doOperation(choice,bookList);
        }

    }

    private static User login() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("請輸入您的姓名：");
        String name = scanner.next();
        System.out.println(name + "歡迎使用！");
        System.out.println("請選擇您的身份：");
        System.out.println(" 0、管理員  1、用戶 ");
        int who = scanner.nextInt();
        if(who == 0){
            return new Admin(name);
        }
        return new NormalUser(name);
    }
}

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