Java stream 排序

数字排序

List students = new ArrayList<>();
Student student1 = new Student("六年级","Math","小张",1D);
students.add(student1);
Student student2 = new Student("三年级上","English","小钱",8D);
students.add(student2);
Student student3 = new Student("五年级","Chinese","小孙",6D);
students.add(student3);

倒序
List collect = students.stream().sorted(Comparator.comparing(Student::getMark).reversed()).collect(Collectors.toList());

控制台：
排序前：1.0|8.0|6.0|
排序后：8.0|6.0|1.0|

正序
List collect = students.stream().sorted(Comparator.comparing(Student::getMark)).collect(Collectors.toList());

控制台：
排序前：1.0|8.0|6.0|
排序后：1.0|6.0|8.0|

以中文排序

List students = new ArrayList<>();
Student student1 = new Student("六年级","Math","小张",1D);
students.add(student1);
Student student2 = new Student("三年级上","English","小钱",8D);
students.add(student2);
Student student3 = new Student("五年级","Chinese","小孙",6D);
students.add(student3);

List collect = students.stream().sorted(Comparator.comparing(Student::getGrade).reversed()).collect(Collectors.toList());

控制台：
排序前：六年级|三年级上|五年级|
排序后：六年级|五年级|三年级上|

List collect = students.stream().sorted(Comparator.comparing(Student::getGrade)).collect(Collectors.toList());

控制台：
排序前：六年级|三年级上|五年级|
排序后：三年级上|五年级|六年级|

排序字段为null时

List students = new ArrayList<>();
Student student1 = new Student("六年级","Math","小张",1D);
students.add(student1);
Student student2 = new Student("三年级上","English","小钱",8D);
students.add(student2);
Student student3 = new Student(null,"Chinese","小孙",6D);
students.add(student3);

List collect = students.stream().sorted(Comparator.comparing(Student::getGrade).reversed()).collect(Collectors.toList());

控制台：
Exception in thread "main" java.lang.NullPointerException
	at java.lang.String.compareTo(String.java:1155)
	at java.lang.String.compareTo(String.java:111)
	at java.util.Comparator.lambda$comparing$77a9974f$1(Comparator.java:469)
	at java.util.Collections$ReverseComparator2.compare(Collections.java:5185)
	at java.util.TimSort.countRunAndMakeAscending(TimSort.java:360)
	at java.util.TimSort.sort(TimSort.java:220)
	at java.util.Arrays.sort(Arrays.java:1512)
	at java.util.stream.SortedOps$SizedRefSortingSink.end(SortedOps.java:348)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:483)
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
	at com.hbis.ttie.mal.rest.Test2.main(Test2.java:29)