前言
这次文章将带大家实现一个图书管理系统，界面如下：
找到对象
我们从上面就可以知道，我们需要创建两个对象，一个是管理员对象，一个是普通用户对象，由于这两个对象都是用户这一范畴，所以我们可以为他们创建一个父类，那我们可以将这三个类放在同一个包上，如下图所示：
然后我们进一步思考我们还需要什么类，由于这是一个图书管理系统，所以我们可以创建书这个类用来创建多本的书，我们还可以创建一个书架用来存放书籍，这两个类我们把他们放在同一个包上：
我们有很多个功能需要实现，例如增加图书，删除图书，查询图书等等…我们可以再创建一个包用来专门存放这些功能：
最后我们需要创建一个Main类用来组装上面的代码，使其成为一个管理系统。
代码实现
book包
Book类
这里的书包括书名，作者，书的类型，价格以及书是否被借出的状态，这样我们可以创建对应的成员变量，为了有封装的体现，我们可以使用private修饰这些创元变量，然后通过Getter and Setter 来实现成员变量的访问就可以了.
由于我们会访问这本书的所有信息，我们就需要打印，这时候我们就要重写toString 方法，尽管IDEA编译器会自动帮我们实现，但是对于书是否被借出的状态打印，我们需要打印字符串（“未借阅” 和 “已借阅”）这两种状态，但是这个成员变量是boolean类型的，所以我们如果不去修改toString 方法的话，我们就会得到false和true这两种打印形式，那么我们就要稍微修改一下代码，这时候我们可以使用三目表达式来进行修改
如果直接使用编译器自动生成 toString 代码：
public Book(String name, String author, String type, double price, boolean is_borrowed) {this.name = name;this.author = author;this.type = type;this.price = price;this.is_borrowed = is_borrowed;}
结合上述的要点，我们可以得到下面的代码：
public class Book {private String name;private String author;private String type;private double price;private boolean is_borrowed;@Overridepublic String toString() {return "Book{" +"name='" + name + '\'' +", author='" + author + '\'' +", type='" + type + '\'' +", price=" + price +(is_borrowed == false ? " 未借阅": " 已借阅") +'}';}public Book(String name, String author, String type, double price) {this.name = name;this.author = author;this.type = type;this.price = price;}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 String getType() {return type;}public void setType(String type) {this.type = type;}public double getPrice() {return price;}public void setPrice(double price) {this.price = price;}public boolean isIs_borrowed() {return is_borrowed;}public void setIs_borrowed(boolean is_borrowed) {this.is_borrowed = is_borrowed;}
}BookList 类 （书架）
我们可以使用组合来将书放在代码里，我们还可以先将三本书放在书架上，这时候我们可以通过构造方法来初始化书架，我们还需要知道书架上目前有多少本书，容量是多少，成员变量要相应的写上去，并且通过getter和setter方法来来实现成员变量的访问…
public class BookList {private Book[] books;private int curSize;private int count;public BookList(){books = new Book[10];books[0] = new Book("三国演义","罗贯中","名著",30.12);books[1] = new Book("西游记","吴承恩","名著",30.14);books[2] = new Book("红楼梦","曹雪芹","名著",50.42);curSize = 3;count = 10;}public int getCurSize() {return curSize;}public void setCurSize(int curSize) {this.curSize = curSize;}public int getCount() {return count;}public void setCount(int count) {this.count = count;}public Book getBooks(int i) {return books[i];}public void setBooks(int pos,Book newBook) {books[pos] = newBook;}
}
user包
我们先来创建父类 User，需要姓名这一个成员变量，由于父类本身是要被继承的，所以我们可以将其实现为抽象类，不同的身份有不同的菜单列表，既然都是菜单我们不妨在父类写一个抽象方法，提醒子类要记得写菜单，还有用户会输入不同的数字来实现不同的功能，这里我们可以创建一个功能实现的方法，这样子我们就可以通过父类的引用来实现不同的子类所对应的功能…
public abstract class User {public String name;protected Ioperate[] opertions;public User(String name) {this.name = name;}public abstract int menu();public void work(int choice, BookList bookList){opertions[choice].operate(bookList);}
}
管理者
public class Manager extends User{public Manager(String name) {super(name);opertions = new Ioperate[] {new Exit(),new Find(),new Add(),new Delete(),new Show()};}@Overridepublic int menu() {System.out.println("*******管理员菜单*******");System.out.println(" 1.查询图书");System.out.println(" 2.增加图书");System.out.println(" 3.删除图书");System.out.println(" 4.显示所有图书");System.out.println(" 0.退出系统");System.out.println("************************");System.out.println("请输入你的选择：");Scanner scan = new Scanner(System.in);int choice = scan.nextInt();return choice;}
}
普通用户
public class DomesticConsumer extends User {public DomesticConsumer(String name) {super(name);opertions = new Ioperate[] {new Exit(),new Find(),new Borrow(),new Return()};}@Overridepublic int menu() {System.out.println("*******普通用户菜单*******");System.out.println(" 1.查询图书");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("请输入你的选择：");Scanner scan = new Scanner(System.in);int choice = scan.nextInt();return choice;}
}
Ioperation包
接口
我们可以通过一个接口来实现功能的有机联系，这样我们就可以通过这个接口类型来实现不同的方法，我们知道这些方法几乎都会操作书架，所以我们将书架作为参数进行传递就可以了。
public interface Ioperate {void operate(BookList bookList);
}
Add
我们直接采用尾插，我们需要判断一下书架是否还能继续放书，需要将目前的图书数目和书架容量进行比较就可以了，接下来就是创建新书，将新书放到书架即可，这时候我们要注意书架放书的代码是否正确，我们使用IDEA编译器只能实现Book[]类型的getter和setter，但是书的类型是Book，所以我们需要自己写一个放书的代码:
public void setBooks(int pos,Book newBook) {books[pos] = newBook;}
为什么不直接写books[curSize] = newBook呢？
因为我们后面删除图书的代码里也是需要对书架上的书进行移动，会用到setter方法，所以为了代码的通用性高，我们就多加了一个pos参数
public class Add implements Ioperate{@Overridepublic void operate(BookList bookList) {int count = bookList.getCount();int curSize = bookList.getCurSize();if(count == curSize){System.out.println("书架已满，无法再放入别的图书.......");return;}System.out.println("请输入你要增加的书名:");Scanner scan = new Scanner(System.in);String name = scan.nextLine();System.out.println("请输入作者名字");String author = scan.nextLine();System.out.println("请输入图书类型：");String type = scan.nextLine();System.out.println("请输入图书价格：");double price = scan.nextDouble();Book newBook = new Book(name,author,type,price);bookList.setBooks(curSize,newBook);bookList.setCurSize(curSize + 1);}
}在进行删除图书，查询图书，这里我采用的是通过书名进行遍历访问的方式。
这时候我们就要小心，因为我们是对书架进行操控的，所以我们要先拿到书这个对象，那我们就要看怎么拿出对应的书，由于编译器只能实现Book[]类型的getter，所以我们还是要自己写一个拿书的代码。
由于书名是String类型，所以可以使用equals方法经行字符串的比对。所以我们拿到书后还要访问书的书名再进行比对即可。
public Book getBooks(int i) {return books[i];}
Book book = bookList.getBooks(i);if(book.getName().equals(name)){//......}
Delete
删除书也很容易，我们需要把待删除的书后面的书进行前移
public class Delete implements Ioperate{@Overridepublic void operate(BookList bookList) {int curSize = bookList.getCurSize();if(curSize == 0){System.out.println("书架已空，无法继续删除......");}System.out.println("请输入你要删除图书的书名：");Scanner scan = new Scanner(System.in);String name = scan.nextLine();for (int i = 0; i < curSize; i++) {Book book = bookList.getBooks(i);if(book.getName().equals(name)){System.out.println("删除成功......");for (int j = i; j < curSize - 1; j++) {bookList.setBooks(j,bookList.getBooks(j+1));}bookList.setCurSize(curSize - 1);return;}}System.out.println("未查询到该书.....");}
}
Borrow
public class Borrow implements Ioperate{@Overridepublic void operate(BookList bookList) {System.out.println("请输入你要借阅图书书名：");Scanner scan = new Scanner(System.in);String name = scan.nextLine();int curSize = bookList.getCurSize();for (int i = 0; i < curSize; i++) {Book book = bookList.getBooks(i);if(book.getName().equals(name)){if(book.isIs_borrowed() == false){System.out.println("该书已被你成功借阅......");book.setIs_borrowed(true);}else{System.out.println("该书已被借阅，无法被再次借阅.....");}return;}}System.out.println("未查询到此书......");}
}
Find
public class Find implements Ioperate{@Overridepublic void operate(BookList bookList) {System.out.println("输入你要查询的书名：");Scanner scan = new Scanner(System.in);String name = scan.nextLine();int count = bookList.getCurSize();for (int i = 0; i < count; i++) {Book book = bookList.getBooks(i);if(book.getName().equals(name)){System.out.println(book);return;}}System.out.println("未查询到此书......");}
}
Return
public class Return implements Ioperate{@Overridepublic void operate(BookList bookList) {System.out.println("请输入你要归还书名：");Scanner scan = new Scanner(System.in);String name = scan.nextLine();int count = bookList.getCurSize();for (int i = 0; i < count; i++) {Book book = bookList.getBooks(i);if(book.getName().equals(name)){if(book.isIs_borrowed() == true){System.out.println("归还成功......");book.setIs_borrowed(false);}else{System.out.println("该图书已被归还到书架上，无需重复归还......");}return;}}System.out.println("未查询到该图书.....");}
}Show
public class Show implements Ioperate{@Overridepublic void operate(BookList bookList) {int count = bookList.getCurSize();for (int i = 0; i < count; i++) {System.out.println(bookList.getBooks(i));}}
}
Exit
退出程序的代码就是System.exit(数字)，数字零表示正常退出的意思。
public class Exit implements Ioperate{@Overridepublic void operate(BookList bookList) {System.out.println("退出系统......");System.exit(0);}
}
登录
我们再Main类写一个login方法
public static User login(){Scanner scan = new Scanner(System.in);System.out.println("请输入你的姓名：");String name = scan.nextLine();System.out.println("1.管理员 2.普通用户");System.out.println("请输入你的身份：");int identity = scan.nextInt();if(identity == 1){return new Manager(name);}else{return new DomesticConsumer(name);}}
主逻辑实现
我们先登录，然后创建书架，接着打印菜单，用户输入指令，计算机进行对应的操作：
public static void main(String[] args) {//创建书架BookList bookList = new BookList();//loginUser user = login();while(true){//功能菜单选择int choice = user.menu();//功能实现user.work(choice,bookList);}}
最终代码
Main类
import book.BookList;
import user.DomesticConsumer;
import user.Manager;
import user.User;import java.util.Scanner;public class Main {public static User login(){Scanner scan = new Scanner(System.in);System.out.println("请输入你的姓名：");String name = scan.nextLine();System.out.println("1.管理员 2.普通用户");System.out.println("请输入你的身份：");int identity = scan.nextInt();if(identity == 1){return new Manager(name);}else{return new DomesticConsumer(name);}}public static void main(String[] args) {//创建书架BookList bookList = new BookList();//loginUser user = login();while(true){//功能菜单选择int choice = user.menu();//功能实现user.work(choice,bookList);}}
}
user包
User
package user;import Ioperation.Ioperate;
import book.BookList;public abstract class User {public String name;protected Ioperate[] opertions;public User(String name) {this.name = name;}public abstract int menu();public void work(int choice, BookList bookList){opertions[choice].operate(bookList);}
}
Manager
package user;import Ioperation.*;import java.util.Scanner;public class Manager extends User{public Manager(String name) {super(name);opertions = new Ioperate[] {new Exit(),new Find(),new Add(),new Delete(),new Show()};}@Overridepublic int menu() {System.out.println("*******管理员菜单*******");System.out.println(" 1.查询图书");System.out.println(" 2.增加图书");System.out.println(" 3.删除图书");System.out.println(" 4.显示所有图书");System.out.println(" 0.退出系统");System.out.println("************************");System.out.println("请输入你的选择：");Scanner scan = new Scanner(System.in);int choice = scan.nextInt();return choice;}
}
DomesticConsumer
package user;import Ioperation.*;import java.util.Scanner;public class DomesticConsumer extends User {public DomesticConsumer(String name) {super(name);opertions = new Ioperate[] {new Exit(),new Find(),new Borrow(),new Return()};}@Overridepublic int menu() {System.out.println("*******普通用户菜单*******");System.out.println(" 1.查询图书");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("请输入你的选择：");Scanner scan = new Scanner(System.in);int choice = scan.nextInt();return choice;}
}
book 包
Book
package book;public class Book {private String name;private String author;private String type;private double price;private boolean is_borrowed;@Overridepublic String toString() {return "Book{" +"name='" + name + '\'' +", author='" + author + '\'' +", type='" + type + '\'' +", price=" + price +(is_borrowed == false ? " 未借阅": " 已借阅") +'}';}public Book(String name, String author, String type, double price) {this.name = name;this.author = author;this.type = type;this.price = price;}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 String getType() {return type;}public void setType(String type) {this.type = type;}public double getPrice() {return price;}public void setPrice(double price) {this.price = price;}public boolean isIs_borrowed() {return is_borrowed;}public void setIs_borrowed(boolean is_borrowed) {this.is_borrowed = is_borrowed;}
}BookList
package book;public class BookList {private Book[] books;private int curSize;private int count;public BookList(){books = new Book[10];books[0] = new Book("三国演义","罗贯中","名著",30.12);books[1] = new Book("西游记","吴承恩","名著",30.14);books[2] = new Book("红楼梦","曹雪芹","名著",50.42);curSize = 3;count = 10;}public int getCurSize() {return curSize;}public void setCurSize(int curSize) {this.curSize = curSize;}public int getCount() {return count;}public void setCount(int count) {this.count = count;}public Book getBooks(int i) {return books[i];}public void setBooks(int pos,Book newBook) {books[pos] = newBook;}
}Ioperation包
Ioperate
package Ioperation;import book.BookList;public interface Ioperate {void operate(BookList bookList);
}
Add
package Ioperation;import book.Book;
import book.BookList;import java.util.Scanner;public class Add implements Ioperate{@Overridepublic void operate(BookList bookList) {int count = bookList.getCount();int curSize = bookList.getCurSize();if(count == curSize){System.out.println("书架已满，无法再放入别的图书.......");return;}System.out.println("请输入你要增加的书名:");Scanner scan = new Scanner(System.in);String name = scan.nextLine();System.out.println("请输入作者名字");String author = scan.nextLine();System.out.println("请输入图书类型：");String type = scan.nextLine();System.out.println("请输入图书价格：");double price = scan.nextDouble();Book newBook = new Book(name,author,type,price);bookList.setBooks(curSize,newBook);bookList.setCurSize(curSize + 1);}
}Borrow
package Ioperation;import book.Book;
import book.BookList;import java.util.Scanner;public class Borrow implements Ioperate{@Overridepublic void operate(BookList bookList) {System.out.println("请输入你要借阅图书书名：");Scanner scan = new Scanner(System.in);String name = scan.nextLine();int curSize = bookList.getCurSize();for (int i = 0; i < curSize; i++) {Book book = bookList.getBooks(i);if(book.getName().equals(name)){if(book.isIs_borrowed() == false){System.out.println("该书已被你成功借阅......");book.setIs_borrowed(true);}else{System.out.println("该书已被借阅，无法被再次借阅.....");}return;}}System.out.println("未查询到此书......");}
}Delete
package Ioperation;import book.Book;
import book.BookList;import java.util.Scanner;public class Delete implements Ioperate{@Overridepublic void operate(BookList bookList) {int curSize = bookList.getCurSize();if(curSize == 0){System.out.println("书架已空，无法继续删除......");}System.out.println("请输入你要删除图书的书名：");Scanner scan = new Scanner(System.in);String name = scan.nextLine();for (int i = 0; i < curSize; i++) {Book book = bookList.getBooks(i);if(book.getName().equals(name)){System.out.println("删除成功......");for (int j = i; j < curSize - 1; j++) {bookList.setBooks(j,bookList.getBooks(j+1));}bookList.setCurSize(curSize - 1);return;}}System.out.println("未查询到该书.....");}
}Exit
package Ioperation;import book.BookList;public class Exit implements Ioperate{@Overridepublic void operate(BookList bookList) {System.out.println("退出系统......");System.exit(0);}
}Find
package Ioperation;import book.Book;
import book.BookList;import java.util.Scanner;public class Find implements Ioperate{@Overridepublic void operate(BookList bookList) {System.out.println("输入你要查询的书名：");Scanner scan = new Scanner(System.in);String name = scan.nextLine();int count = bookList.getCurSize();for (int i = 0; i < count; i++) {Book book = bookList.getBooks(i);if(book.getName().equals(name)){System.out.println(book);return;}}System.out.println("未查询到此书......");}
}Return
package Ioperation;import book.Book;
import book.BookList;import java.util.Scanner;public class Return implements Ioperate{@Overridepublic void operate(BookList bookList) {System.out.println("请输入你要归还书名：");Scanner scan = new Scanner(System.in);String name = scan.nextLine();int count = bookList.getCurSize();for (int i = 0; i < count; i++) {Book book = bookList.getBooks(i);if(book.getName().equals(name)){if(book.isIs_borrowed() == true){System.out.println("归还成功......");book.setIs_borrowed(false);}else{System.out.println("该图书已被归还到书架上，无需重复归还......");}return;}}System.out.println("未查询到该图书.....");}
}Show
package Ioperation;import book.BookList;public class Show implements Ioperate{@Overridepublic void operate(BookList bookList) {int count = bookList.getCurSize();for (int i = 0; i < count; i++) {System.out.println(bookList.getBooks(i));}}
}
