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  1. import java.time.LocalDate;
  2. import java.util.*;
  3. import java.util.stream.Collectors;
  4.  
  5. class Student {
  6.     private Integer id;
  7.     private String name;
  8.     private LocalDate birthDate;
  9.     private List<Double> grades = new ArrayList<>();
  10.  
  11.     public Student(String name, LocalDate birthDate, Double... grades) {
  12.         this.name = name;
  13.         this.birthDate = birthDate;
  14.         Collections.addAll(this.grades, grades);
  15.     }
  16.  
  17.     public List<Double> getGrades() {
  18.         return grades;
  19.     }
  20.  
  21.     public void addGrade(double grade) {
  22.         grades.add(grade);
  23.     }
  24.  
  25.     public LocalDate getBirthDate() {
  26.         return birthDate;
  27.     }
  28.  
  29.     public Integer getId() {
  30.         return id;
  31.     }
  32.  
  33.     public void setId(Integer id) {
  34.         this.id = id;
  35.     }
  36.  
  37.     @Override
  38.     public String toString() {
  39.         return "Student{" +
  40.                 "id=" + id +
  41.                 ", name='" + name + '\'' +
  42.                 ", birthDate=" + birthDate +
  43.                 ", grades=" + grades +
  44.                 '}';
  45.     }
  46. }
  47.  
  48. class StudentService {
  49.     private Map<Integer, Student> map = new HashMap<>();
  50.  
  51.     public void saveOrUpdate(Student student) {
  52.         if (student.getId() == null)
  53.             student.setId(map.size());
  54.         else if (student.getId() >= map.size())
  55.             throw new IllegalArgumentException("student id should be <" + map.size());
  56.         map.put(student.getId(), student);
  57.     }
  58.  
  59.     public Student findById(int studentId) {
  60.         return map.get(studentId);
  61.     }
  62.  
  63.     public List<Student> findAllSortedByAge() {
  64.         return map.values().stream()
  65.                 .sorted((s1, s2) -> s2.getBirthDate().compareTo(s1.getBirthDate()))
  66.                 .collect(Collectors.toList());
  67.     }
  68.  
  69.     public Double countAvgOfGrades(Student student) {
  70.         return student.getGrades().stream()
  71.                 .mapToDouble(m -> m)
  72.                 .average()
  73.                 .orElse(0);
  74.     }
  75.  
  76.     public List<Student> findAllWithAvgOfGradesLessThen(double avg) {
  77.         return map.values().stream()
  78.                 .filter(s -> countAvgOfGrades(s) < avg)
  79.                 .collect(Collectors.toList());
  80.     }
  81. }
  82.  
  83. public class Main {
  84.     public static void main(String[] args) {
  85.         StudentService studentService = new StudentService();
  86.  
  87.         studentService.saveOrUpdate(new Student("aaaaa",
  88.                 LocalDate.parse("1993-01-01"), 4.5, 5.0));
  89.         studentService.saveOrUpdate(new Student("bbbbb",
  90.                 LocalDate.parse("1992-01-01"), 5.5, 5.0, 3.0));
  91.         studentService.saveOrUpdate(new Student("ccccc",
  92.                 LocalDate.parse("1994-01-01"), 3.5));
  93.  
  94.         Student founded = studentService.findById(0);
  95.         System.out.println(founded);
  96.         System.out.println(studentService.countAvgOfGrades(founded));
  97.  
  98.         System.out.println(studentService.findAllSortedByAge());
  99.         System.out.println(studentService.findAllWithAvgOfGradesLessThen(4.0));
  100.     }
  101. }
Compilation error #stdin compilation error #stdout 0s 0KB
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stdin
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Standard input is empty
compilation info 
Main.java:65: error: ')' expected
                .sorted((s1, s2) -> s2.getBirthDate().compareTo(s1.getBirthDate()))
                           ^
Main.java:65: error: illegal start of expression
                .sorted((s1, s2) -> s2.getBirthDate().compareTo(s1.getBirthDate()))
                                  ^
Main.java:65: error: ';' expected
                .sorted((s1, s2) -> s2.getBirthDate().compareTo(s1.getBirthDate()))
                                                                                  ^
Main.java:71: error: illegal start of expression
                .mapToDouble(m -> m)
                                ^
Main.java:78: error: illegal start of expression
                .filter(s -> countAvgOfGrades(s) < avg)
                           ^
5 errors
stdout
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Standard output is empty
https://ideone.com/pLnOl4
language:
Java (HotSpot 12)
created:
9 years ago
visibility:
public

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