集合中的对象排序

对应的实体类：

public class Book implements Comparable<Book>{    private int bookId;    public Book() {        // TODO Auto-generated constructor stub    }    public Book(int bookId){        this.bookId=bookId;    }    public int getBookId() {        return bookId;    }    @Override    public String toString() {        return "Book [bookId=" + bookId + "]";    }    @Override    public int compareTo(Book o) {        if(this.bookId>o.bookId){            return 1 ;        }else if(this.bookId<o.bookId){            return -1 ;        }else{            return 0;        }    }}

测试类：

public class Test {    public static void main(String[] args){           List list=new ArrayList();        Book book1=new Book(1001);        Book book2=new Book(1002);        Book book3=new Book(1003);        Book book4=new Book(1003);        list.add(book1);        list.add(book2);        list.add(book3);        list.add(book4);        System.out.println(list);    }}

结果：
[Book [bookId=1001], Book [bookId=1002], Book [bookId=1003], Book [bookId=1003]]