Java stream 排序
数字排序
- List<Student> 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<Student> 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<Student> 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<Student> 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<Student> 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<Student> 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<Student> 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<Student> 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$comparinga9974f(Comparator.java:469)
- at java.util.Collections$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)
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