refactor: change recordBookNumber type to int and add copy methods

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

@@ -5,17 +5,17 @@ import java.util.Objects;
 public class Student {
     private final String groupNumber;
     private final double averageGrade;
-    private final String recordBookNumber;
+    private final int recordBookNumber;
 
-    Student(String groupNumber, double averageGrade, String recordBookNumber) {
+    public Student(String groupNumber, double averageGrade, int recordBookNumber) {
         if (groupNumber == null || groupNumber.isBlank()) {
             throw new IllegalArgumentException("Group number cannot be empty");
         }
         if (averageGrade < 0.0 || averageGrade > 5.0) {
             throw new IllegalArgumentException("Average grade must be between 0.0 and 5.0");
         }
-        if (recordBookNumber == null || recordBookNumber.isBlank()) {
+        if (recordBookNumber <= 0) {
-            throw new IllegalArgumentException("Record book number cannot be empty");
+            throw new IllegalArgumentException("Record book number must be positive");
         }
         this.groupNumber = groupNumber;
         this.averageGrade = averageGrade;
@@ -30,42 +30,43 @@ public class Student {
         return averageGrade;
     }
 
-    public String getRecordBookNumber() {
+    public int getRecordBookNumber() {
         return recordBookNumber;
     }
 
+    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 + '\'' +
                 ", averageGrade=" + averageGrade +
-                ", recordBookNumber='" + recordBookNumber + '\'' +
+                ", recordBookNumber=" + recordBookNumber +
                 '}';
     }
 
     @Override
     public boolean equals(Object obj) {
-        if (this == obj) {
+        if (this == obj) return true;
-            return true;
+        if (obj == null || getClass() != obj.getClass()) return false;
-        }
-
-        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
-                && Objects.equals(groupNumber, student.groupNumber)
+                && recordBookNumber == student.recordBookNumber
-                && Objects.equals(recordBookNumber, student.recordBookNumber);
+                && Objects.equals(groupNumber, student.groupNumber);
     }
 
     @Override
     public int hashCode() {
         return Objects.hash(groupNumber, averageGrade, recordBookNumber);
     }
-}
+}