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java根据字符串对自定义对象列表进行排序（7个答案）
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我编写了一个工作方法，将对象插入sortedarraylist类中的ArrayList。问题是，它按arraylist第一个元素的第一个字母排序。
我希望能够选择arraylist的排序方式（例如，根据姓氏的第一个字母或用户对象中的书籍数量）。我该如何处理这个问题？
存储对象类型的示例：user（string firstname，string lasname，int books）

import java.io.*;
import java.util.Scanner;

public class Driver {

    //These SortedArrayLists have been derived from the sorted arraylist class
    public static SortedArrayList<User> sortedUsers = new SortedArrayList<>();

    public static SortedArrayList<Book> sortedBooks = new SortedArrayList<>();

    //This static method checks that input matches records and then sets the loaning user information
    //for the book to be loaned while incrementing the number of books held by the user.
    public static void loanBook(Book book, User user){
        for (Book b : sortedBooks){
            if(b.equals(book)) {

                b.setLoanStatus(true);

                b.setLoaningUser(user);

                break;
            }
        }
        for (User u: sortedUsers){
            if(u.equals(user)){
                u.setNumberOfBooks(u.getNumberOfBooks()+1); //The number of books of a given object is found then incremented by one to create the new value, which is set
                break;

            }
        }
    }

    //This static method checks that input matches records and clears loaning user information
    //for the book to be loaned while lowering the number of books held by the user by 1.
    public static void returnBook(Book book, User user){
        for (Book b : sortedBooks){
            if(b.equals(book)){
                 b.setLoanStatus(false);
                 b.setLoaningUser(null);
                break;
            }

            }
            for (User u: sortedUsers){
                if(u.equals(user)){

                    u.setNumberOfBooks(u.getNumberOfBooks()-1);
                    //The number of books for the object instance of a user in question is decreased since they have returned a book and thus have one less book.

                }
            }

    }

    //This is the main method from which the program starts.
    public static void main(String[] args) throws FileNotFoundException, User.InvalidBookLimitException {

       }

        mainMenu(); //main menu printing method
        char ch = sc.next().charAt(0);
        sc.nextLine();
        while (ch !='f') //the program ends as desired if f is pressed

        { switch(ch){

            case 'b':
                System.out.println("Displaying information about all books in the library: ");
                  //This toString replace method removes unwanted items for a cleaner print of book object information and removes the string description for user's name described in the user toString method.
                System.out.println(sortedBooks.toString().replace("[","").replace("]","").replace("Name: ", ""));

                break;
            case 'u':
                System.out.println("Displaying information about all users");

                System.out.println(sortedUsers.toString().replace("[","").replace("]",""));

                break;

            case 'i':
                System.out.println("Enter the loaning out data. ");

                User user = readNames();

                Book book = readBookName();
                //A book object is created based on user input, then an attempt at altering the
                // relevant object information is made via the loanBook method.
                loanBook(book, user);

                break;
            case 'r':
                System.out.println("Please the details of the book to be returned: ");

                User userReturn = readNames();

                Book bookReturn = readBookName();
                //User input is used to create user and book objects so that a book can be returned
                //by use of the returnBook method, resetting any user information about the book and decreasing the count for number of booksheld by the user.
                returnBook(bookReturn, userReturn);

                break;

            default:  //this case occurs if input does not match any of the switch statement cases.
                System.out.println("Invalid input, please enter f, b, i or r");

        }
        mainMenu();
        ch = sc.next().charAt(0);
            sc.nextLine();
        }

    }
}

sortedarraylist类：import java.util.arraylist；

public class SortedArrayList<E extends Comparable<E>> extends ArrayList<E> {

    //This insert method ensures that an object added to an arraylist is added in a sorted order.
    public void insert(E value) {
        if (this.size() == 0){
            this.add(value);
            return; }
        for (int i = 0; i < this.size(); i++) {
            int comparison = value.compareTo((E) this.get(i) );
            if (comparison < 0) {
                this.add(i, value);
                return; }
            if (comparison == 0){
                return; }
        }
        this.add(value);
    }