面向对象设计原则-迪米特法则示例

public class Book {
    private String title;
    private String author;
    private String publisher;
    
    public Book(String title, String author, String publisher) {
        this.title = title;
        this.author = author;
        this.publisher = publisher;
    }
    
    // 省略其他方法和属性的定义
}

public class Library {
    private String name;
    private String address;
    private List<Book> books;
    
    public Library(String name, String address) {
        this.name = name;
        this.address = address;
        this.books = new ArrayList<>();
    }
    
    public void addBook(Book book) {
        books.add(book);
    }
    
    public void lendBook(Book book, User user) {
        // 省略借出书籍的具体实现
    }
    
    // 省略其他方法和属性的定义
}

public class User {
    private String name;
    private String phone;
    private List<Book> borrowedBooks;
    
    public User(String name, String phone) {
        this.name = name;
        this.phone = phone;
        this.borrowedBooks = new ArrayList<>();
    }
    
    public void borrowBook(Book book, Library library) {
        // 省略借书的具体实现
    }
    
    public void returnBook(Book book, Library library) {
        // 省略还书的具体实现
    }
    
    // 省略其他方法和属性的定义
}

typescriptCopy codepublic class Borrow {
    private Date borrowDate;
    private Date returnDate;
    private Book book;
    private User user;
    
    public Borrow(Book book, User user) {
        this.book = book;
        this.user = user;
        this.borrowDate = new Date();
    }
    
    public void returnBook() {
        this.returnDate = new Date();
        // 省略还书后的其他处理
    }
    
    // 省略其他方法和属性的定义
}

typescriptCopy codepublic class Library {
    private String name;
    private String address;
    private List<Book> books;
    private List<Borrow> borrows;
    
    public Library(String name, String address) {
        this.name = name;
        this.address = address;
        this.books = new ArrayList<>();
        this.borrows = new ArrayList<>();
    }
    
    public void addBook(Book book) {
        books.add(book);
    }
    
    public void lendBook(Book book, User user) {
        // 检查这本书是否可借
        if (!books.contains(book)) {
            throw new IllegalArgumentException("该图书馆没有这本书！");
        }
        for (Borrow borrow : borrows) {
            if (borrow.getBook().equals(book) && borrow.getReturnDate() == null) {
                throw new IllegalArgumentException("这本书已经被借走了！");
            }
        }
        // 创建一个新的借书记录
        Borrow borrow = new Borrow(book, user);
        borrows.add(borrow);
    }
    
    // 省略其他方法和属性的定义
}

public class User {
    private String name;
    private String phone;
    private List<Borrow> borrows;
    
    public User(String name, String phone) {
        this.name = name;
        this.phone = phone;
        this.borrows = new ArrayList<>();
    }
    
    public void borrowBook(Book book, Library library) {
        library.lendBook(book, this);
    }
    
    public void returnBook(Book book, Library library) {
        for (Borrow borrow : borrows){
        if (borrow.getBook().equals(book) && borrow.getReturnDate() == null) {
                borrow.returnBook();
                return;
            }
        }
        throw new IllegalArgumentException("你没有借过这本书！");
    }
    
    // 省略其他方法和属性的定义
}