arraylist sorting in order

问题

Attempting to sort arraylist in alphabetical order but the Collection.sort is giving me an error which i do not what to do with it

import java.util.ArrayList;
import java.util.Collection;

/**
 *
 * @author user
 */
public class BookShelf {

    ArrayList<Book> listOfBooks = new ArrayList<Book>();

    public void addBook(Book book) {
        listOfBooks.add(book);
    }

    public ArrayList<Book> returnListOfBooks() {

        ArrayList<Book> myBook = new ArrayList<Book>(listOfBooks);  
        Collection.sort(myBook);
        return myBook;
    }

any help on how to fix this? thanks a lot!

Edit*

Just need to return an arraylist of books which is in order, after changing to Collections, I've gotten another difficulty.

I've change collection import as well

import java.util.ArrayList;
import java.util.Collections;

回答1:

You are using the wrong class. The Class containing the sort(...) method is Collections not Collection

回答2:

You should be using the Class Collections not Collection

Collections.sort(myBook);

If you don't have duplicates I suggest you to use a TreeSet.

回答3:

Your using user defined custom class So you need to implement comparable/comparator interface to support sorting

see the below example :

class Book implements Comparable<Book>
{
    private String bookName;

    public Book(String bookName) {
        this.bookName = bookName;
    }

    public String getBookName() {
        return bookName;
    }

    public void setBookName(String bookName) {
        this.bookName = bookName;
    }

    @Override
    public int compareTo(Book o) {
        return this.bookName.compareTo(o.bookName);
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 53 * hash + Objects.hashCode(this.bookName);
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final Book other = (Book) obj;
        if (!Objects.equals(this.bookName, other.bookName)) {
            return false;
        }
        return true;
    }


}

Now You can use sort

//List<Book> list1  = new ArrayList<>();

//Collections.sort(list1);

来源：https://stackoverflow.com/questions/33785901/arraylist-sorting-in-order

标签

java

sorting

arraylist

collections