Added example with set which contains mutable values.

Author: Alexis-Dia

src/by/bntu/fitr/povt/immutable/case5/Student.java

@@ -40,4 +40,22 @@ public String toString() {
     public int compareTo(Student o) {
         return this.getAge() - o.getAge();
     }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (!(o instanceof Student)) return false;
+
+        Student student = (Student) o;
+
+        if (name != null ? !name.equals(student.name) : student.name != null) return false;
+        return age != null ? age.equals(student.age) : student.age == null;
+    }
+
+    @Override
+    public int hashCode() {
+        int result = name != null ? name.hashCode() : 0;
+        result = 31 * result + (age != null ? age.hashCode() : 0);
+        return result;
+    }
 }

src/by/bntu/fitr/povt/immutable/case6/Main.java

@@ -0,0 +1,42 @@
+package by.bntu.fitr.povt.immutable.case6;
+
+import by.bntu.fitr.povt.immutable.case5.Student;
+import org.junit.Test;
+
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+import static org.junit.Assert.*;
+
+/**
+ * @author Alexey Druzik on 11.12.2020
+ */
+public class Main {
+
+    @Test
+    public void testOfUnmodifiableSet(){
+        Set<Student> mutableSet = new HashSet<>();
+        Student student1 = new Student("Alex", 21);
+        mutableSet.add(student1);
+
+        Set<Student> unmodifiableSet = Collections.unmodifiableSet(mutableSet);
+        Student student2 = new Student("Bob", 22);
+        assertThrows(UnsupportedOperationException.class,
+            () -> unmodifiableSet.add(student2));
+    }
+
+    @Test
+    public void testOfUpdatingSetWithMutableValues(){
+        Set<Student> setWithMutableValues = new HashSet<>();
+        Student student = new Student("Alex", 21);
+        setWithMutableValues.add(student);
+        boolean studentIsExists = setWithMutableValues.contains(student);
+        System.out.println(studentIsExists);
+        student.setName("Bob");
+        student.setAge(20);
+        studentIsExists = setWithMutableValues.contains(student);
+        System.out.println(studentIsExists);
+        assertFalse(studentIsExists);
+    }
+}