问题描述
有一个list 集合,包含name,可空。date 非空。现在需要排序。需要name 是null 的排在前面,然后按照date排序
问题出现的环境背景及自己尝试过哪些方法
list.sort();
相关代码
// 请把代码文本粘贴到下方(请勿用图片代替代码)
List<Person> people = new ArrayList<>();
people.add(new Person(1,null, sdf.parse("2019-09-23 12:12:12")));
people.add(new Person(2,"1", sdf.parse("2019-09-23 12:12:12")));
people.add(new Person(3,null, sdf.parse("2019-09-24 12:12:12")));
people.add(new Person(4,"1", sdf.parse("2019-09-24 12:12:12")));
people.add(new Person(5,null, sdf.parse("2019-09-17 12:12:12")));
people.add(new Person(6,null, sdf.parse("2019-09-24 12:12:12")));
people.add(new Person(8,null, sdf.parse("2019-09-20 12:12:12")));
people.add(new Person(9,null, sdf.parse("2019-09-23 12:12:12")));
people.add(new Person(10,"1", sdf.parse("2019-09-20 12:12:12")));
people.sort((t1, t2) -> {
if (t1.getName() == null&&t2.getName()!=null) {
return -1;
} else if (t2.getName() == null&&t1.getName()!=null) {
return -1;
} else if (Objects.equals(t1.getName(),t2.getName())) {
return t1.getEntryDate().compareTo(t2.getEntryDate());
} else {
return t1.getName().compareTo(t2.getName());
}
});
System.out.println("SORT===========================");
println(people);
你期待的结果是什么?实际看到的错误信息又是什么?
期望结果:
Person [id=5, name=null, entryDate=2019-09-17 12:12:12]
Person [id=8, name=null, entryDate=2019-09-20 12:12:12]
Person [id=9, name=null, entryDate=2019-09-23 12:12:12]
Person [id=1, name=null, entryDate=2019-09-23 12:12:12]
Person [id=3, name=null, entryDate=2019-09-24 12:12:12]
Person [id=6, name=null, entryDate=2019-09-24 12:12:12]
Person [id=10, name=1, entryDate=2019-09-20 12:12:12]
Person [id=2, name=1, entryDate=2019-09-23 12:12:12]
Person [id=4, name=1, entryDate=2019-09-24 12:12:12]
输出结果:
SORT===========================
Person [id=10, name=1, entryDate=2019-09-20 12:12:12]
Person [id=5, name=null, entryDate=2019-09-17 12:12:12]
Person [id=8, name=null, entryDate=2019-09-20 12:12:12]
Person [id=9, name=null, entryDate=2019-09-23 12:12:12]
Person [id=4, name=1, entryDate=2019-09-24 12:12:12]
Person [id=3, name=null, entryDate=2019-09-24 12:12:12]
Person [id=2, name=1, entryDate=2019-09-23 12:12:12]
Person [id=1, name=null, entryDate=2019-09-23 12:12:12]
Person [id=6, name=null, entryDate=2019-09-24 12:12:12]
你写错了,你现在不管t1.name是null,还是t2.name是null都返回-1,应该是