catch(ParseException e || NumberFormatException e)有什么问题

这行代码有语法错误，catch语句中只能捕获单一异常类型，不能使用逻辑运算符“||”来捕获多个异常类型。如果想要捕获多个异常类型，可以使用多个catch语句来分别捕获不同的异常类型，例如：

try {
    // 可能会抛出异常的代码
} catch (ParseException e) {
    // 处理ParseException异常的代码
} catch (NumberFormatException e) {
    // 处理NumberFormatException异常的代码
}

相关问题

write java。The moreBook method takes the name of a user and a number of books (as a string) as arguments. The moreBook method of the controller then transforms the number of books from a string to an integer (using the Integer.parseInt static method) and calls the moreBook method of the library to increase the number of books borrowed or lent by the user (depending on what kind of user it is) of a specific user, by the given argument. • If no exception occurs then the moreBook method of the controller returns the empty string. • If the moreBook method of the library throws an UnknownUserException then the moreBook method of the controller must catch this exception and return as result the error message from the exception object. • If the moreBook method of the library throws a NotALenderException then the moreBook method of the controller must catch this exception and return as result the error message from the exception object. • If the parseInt method of the Integer class throws a NumberFormatException (because the user typed something which is not an integer) then the moreBook method of the controller must catch this exception and return as result the error message from the exception object.

Here is the Java code for the described functionality:

public class LibraryController {
    private Library library;
    
    public LibraryController(Library library) {
        this.library = library;
    }
    
    public String moreBook(String userName, String numBooks) {
        try {
            int num = Integer.parseInt(numBooks);
            library.moreBook(userName, num);
            return "";
        } catch (UnknownUserException e) {
            return e.getMessage();
        } catch (NotALenderException e) {
            return e.getMessage();
        } catch (NumberFormatException e) {
            return e.getMessage();
        }
    }
}

public class Library {
    private Map<String, User> users;
    
    public Library() {
        users = new HashMap<>();
    }
    
    public void moreBook(String userName, int numBooks) throws UnknownUserException, NotALenderException {
        User user = users.get(userName);
        if (user == null) {
            throw new UnknownUserException("Unknown user: " + userName);
        }
        if (!(user instanceof Lender)) {
            throw new NotALenderException(userName + " is not a lender");
        }
        ((Lender) user).moreBooks(numBooks);
    }
}

public class User {
    private String name;
    
    public User(String name) {
        this.name = name;
    }
    
    public String getName() {
        return name;
    }
}

public class Lender extends User {
    private int numBooks;
    
    public Lender(String name) {
        super(name);
        numBooks = 0;
    }
    
    public int getNumBooks() {
        return numBooks;
    }
    
    public void moreBooks(int num) {
        numBooks += num;
    }
}

public class UnknownUserException extends Exception {
    public UnknownUserException(String message) {
        super(message);
    }
}

public class NotALenderException extends Exception {
    public NotALenderException(String message) {
        super(message);
    }
}

The LibraryController class has a constructor that takes a Library object as a parameter. The moreBook method takes a user name and a number of books as arguments. It uses the Integer.parseInt static method to parse the number of books from a string to an integer. It then calls the moreBook method of the Library object to increase the number of books borrowed or lent by the user, depending on what kind of user it is.

If no exception occurs, the moreBook method of the controller returns the empty string. If the moreBook method of the library throws an UnknownUserException, the moreBook method of the controller catches this exception and returns the error message from the exception object. If the moreBook method of the library throws a NotALenderException, the moreBook method of the controller catches this exception and returns the error message from the exception object. If the parseInt method of the Integer class throws a NumberFormatException, the moreBook method of the controller catches this exception and returns the error message from the exception object.

The Library class has a map of users, where the key is the user name and the value is a User object. The moreBook method takes a user name and a number of books as arguments. It throws an UnknownUserException if the user is not found in the map, and a NotALenderException if the user is not an instance of the Lender class. Otherwise, it calls the moreBooks method of the Lender object to increase the number of books borrowed by the user.

The User class has a name field and a getName method.

The Lender class extends the User class and adds a numBooks field and a moreBooks method.

The UnknownUserException and NotALenderException classes extend the Exception class and have constructors that take an error message as a parameter.

write java。The create method takes as arguments the name of a new library user, a number of books (as a string), and an integer representing the role of user to create (where the integer 0 means a lender and the integer 1 means a borrower). The create method of the controller then transforms the book number from a string to an integer (using the Integer.parseInt static method), creates an object from the correct class (based on the role specified by the user input: lender or borrower) and calls the addUser method of the library to add the new user object to the library. • If no exception occurs then the create method of the controller returns the empty string. • If the constructor of the Borrower class throws a NotALenderException then the create method of the controller must catch this exception and return as result the error message from the exception object. • If the parseInt method of the Integer class throws a NumberFormatException (because the user typed something which is not an integer) then the create method of the controller must catch this exception and return as result the error message from the exception object.

Here is a possible implementation of the `create` method in Java:

public class LibraryController {
    private Library library;
    
    public LibraryController(Library library) {
        this.library = library;
    }
    
    public String create(String name, String bookString, int role) {
        try {
            int bookCount = Integer.parseInt(bookString);
            User user;
            if (role == 0) {
                user = new Lender(name, bookCount);
            } else if (role == 1) {
                user = new Borrower(name, bookCount);
            } else {
                return "Invalid role: " + role;
            }
            library.addUser(user);
            return "";
        } catch (NotALenderException e) {
            return e.getMessage();
        } catch (NumberFormatException e) {
            return "Invalid book count: " + bookString;
        }
    }
}

In this implementation, the `create` method takes three arguments: the name of the new user, the book count as a string, and the role as an integer. The method first tries to parse the book count using `Integer.parseInt`, and if successful, creates a user object based on the role specified by the user input. If the role is not 0 or 1, an error message is returned.

If the user object is successfully created, the method calls the `addUser` method of the library to add the new user object to the library. If no exception occurs, an empty string is returned.

If the constructor of the `Borrower` class throws a `NotALenderException`, the method catches the exception and returns the error message from the exception object.

If the `parseInt` method of the `Integer` class throws a `NumberFormatException` (because the user typed something which is not an integer), the method catches the exception and returns an error message indicating that the book count is invalid.