Question

我正在尝试对ArrayList w.r.t termDate进行排序。 ArrayList包含firstName，lastName，email，startDate，termDate，Status

日期可以为空或为空。我必须相应地进行比较，并将所有空/空日期值放在最后。

Collections.sort(usersList, new Comparator<User>() {
                public int compare(User o1, User o2) {
                    System.out.println("Term Date: " + o1.getTermDate() +" " +o2.getTermDate());
                    if((o1.getTermDate() == null || "".equals(o1.getTermDate())) && (o2.getTermDate() == null || "".equals(o2.getTermDate()))) {
                        System.out.println("Term Date1: 0 " + o1.getTermDate() + " " + o2.getTermDate());
                        return 0; //They are both null, both equal
                    }
                    if((o1.getTermDate() == null || "".equals(o1.getTermDate())) && (o2.getTermDate() != null || "".equals(o2.getTermDate()))) {
                        System.out.println("Term Date2: -1 " + o1.getTermDate() + " " + o2.getTermDate());
                        return -1; // The first is null and the second is not, return the first as lower than the second
                    }
                    if((o1.getTermDate() != null || "".equals(o1.getTermDate())) && (o2.getTermDate() == null || "".equals(o2.getTermDate()))) {
                        System.out.println("Term Date3: 1 " + o1.getTermDate() + " " + o2.getTermDate());
                        return 1; //The first is not null and the second is, return the first as higher than the second
                    }
                    else {
                        System.out.println("Term Date4: " + o1.getTermDate() + " " + o2.getTermDate());
                        return o1.getTermDate().compareTo(o2.getTermDate()); //Return the actual comparison
                    }
                }
            });

部分sysouts：

Term Date: null 2015-08-31 00:00:00.0
Term Date2: -1 null 2015-08-31 00:00:00.0
Term Date: null null
Term Date1: 0 null null
Term Date: 2015-08-31 00:00:00.0 null
Term Date3: 1 2015-08-31 00:00:00.0 null
Term Date: 2015-08-31 00:00:00.0 null
Term Date3: 1 2015-08-31 00:00:00.0 null
Term Date: 2015-08-31 00:00:00.0 null
Term Date3: 1 2015-08-31 00:00:00.0 null
Term Date: 2015-08-31 00:00:00.0 null
Term Date3: 1 2015-08-31 00:00:00.0 null
Term Date: 2015-08-31 00:00:00.0 2015-08-31 00:00:00.0
Term Date4: 2015-08-31 00:00:00.0 2015-08-31 00:00:00.0

部分输出：

user,five,user5@gmail.com,08/07/2015,,Active
usernew2,two,usernew2@gmail.com,08/11/2015,,Active
myname2,hello3,qwerty1@gmail.com,08/11/2015,,Active
user,noUserAuth,user_nouserauth@gmail.com,08/21/2015,,Active

Answer 1

根据您的代码，我假设您的日期是 String 对象（当您将它们与空字符串进行比较时），当我查看输出时，日期按字母顺序排序，这是这个假设的预期输出。

解决方案：更改模型并使用LocalDate（在Java 8上）或Date（在Java 8之前）作为数据类型。或者（不推荐），您可以在比较时将字符串转换为LocalDate（这本身就比较慢）。

Answer 2

TermDate的类型是什么？如果是String，则将其解析为日期。（如果你在这个日期有工作要做，你永远不应该有一个日期的字符串表示）要比较两个日期，请在一个为null时定义您的comportment，对于一般情况，返回date1.compareTo（date2）

Collections.sort（）日期不起作用

2 个答案: