fix: make constants private, return hashCode check in equals

app/src/main/java/ru/project/student/Student.java

@@ -3,11 +3,10 @@ package ru.project.student;
 import java.util.Objects;
 
 public class Student {
-
+    private static final double MIN_AVERAGE_GRADE = 0.0;
-    public static final double MIN_AVERAGE_GRADE = 0.0;
+    private static final double MAX_AVERAGE_GRADE = 5.0;
-    public static final double MAX_AVERAGE_GRADE = 5.0;
+    private static final int MIN_RECORD_BOOK_NUMBER = 1;
-    public static final int MIN_RECORD_BOOK_NUMBER = 1;
+    private static final String GROUP_NUMBER_PATTERN = "^[A-Z][0-9]{2}$";
-    public static final String GROUP_NUMBER_PATTERN = "^[A-Z][0-9]{2}$";
 
     private final String groupNumber;
     private final double averageGrade;
@@ -16,15 +15,18 @@ public class Student {
     public Student(String groupNumber, double averageGrade, int recordBookNumber) {
         if (groupNumber == null || !groupNumber.matches(GROUP_NUMBER_PATTERN)) {
             throw new IllegalArgumentException(
-                    "Group number must match pattern: " + GROUP_NUMBER_PATTERN);
+                    "Group number must match pattern: " + GROUP_NUMBER_PATTERN
+            );
         }
         if (averageGrade < MIN_AVERAGE_GRADE || averageGrade > MAX_AVERAGE_GRADE) {
             throw new IllegalArgumentException(
-                    "Average grade must be between " + MIN_AVERAGE_GRADE + " and " + MAX_AVERAGE_GRADE);
+                    "Average grade must be between " + MIN_AVERAGE_GRADE + " and " + MAX_AVERAGE_GRADE
+            );
         }
         if (recordBookNumber < MIN_RECORD_BOOK_NUMBER) {
             throw new IllegalArgumentException(
-                    "Record book number must be at least " + MIN_RECORD_BOOK_NUMBER);
+                    "Record book number must be at least " + MIN_RECORD_BOOK_NUMBER
+            );
         }
         this.groupNumber = groupNumber;
         this.averageGrade = averageGrade;
@@ -43,16 +45,8 @@ public class Student {
         return recordBookNumber;
     }
 
-    public Student withGroupNumber(String groupNumber) {
+    public static double getMinAverageGrade() {
-        return new Student(groupNumber, this.averageGrade, this.recordBookNumber);
+        return MIN_AVERAGE_GRADE;
-    }
-
-    public Student withAverageGrade(double averageGrade) {
-        return new Student(this.groupNumber, averageGrade, this.recordBookNumber);
-    }
-
-    public Student withRecordBookNumber(int recordBookNumber) {
-        return new Student(this.groupNumber, this.averageGrade, recordBookNumber);
     }
 
     public static double getMaxAverageGrade() {
@@ -67,6 +61,19 @@ public class Student {
         return GROUP_NUMBER_PATTERN;
     }
 
+    public Student withGroupNumber(String groupNumber) {
+        return new Student(groupNumber, this.averageGrade, this.recordBookNumber);
+    }
+
+    public Student withAverageGrade(double averageGrade) {
+        return new Student(this.groupNumber, averageGrade, this.recordBookNumber);
+    }
+
+    public Student withRecordBookNumber(int recordBookNumber) {
+        return new Student(this.groupNumber, this.averageGrade, recordBookNumber);
+    }
+
+    @Override
     public String toString() {
         return "Student{" +
                 "groupNumber='" + groupNumber + '\'' +
@@ -83,6 +90,9 @@ public class Student {
         if (obj == null || getClass() != obj.getClass()) {
             return false;
         }
+        if (this.hashCode() != obj.hashCode()) {
+            return false;
+        }
         Student student = (Student) obj;
         return Double.compare(averageGrade, student.averageGrade) == 0
                 && recordBookNumber == student.recordBookNumber