BAEL-6633 (#14308)

* Deep copy of Arraylist

* Deep copy of Arraylist

* Deep copy of Arraylist updated as per review

core-java-modules/core-java-lang-oop-patterns/src/main/java/com/baeldung/deepcopyarraylist/Course.java

@@ -0,0 +1,42 @@
+package com.baeldung.deepcopyarraylist;
+
+import java.io.Serializable;
+
+public class Course implements Serializable, Cloneable {
+
+    private Integer courseId;
+    private String courseName;
+
+    public Course() {
+    }
+
+    public Course(Integer courseId, String courseName) {
+        this.courseId = courseId;
+        this.courseName = courseName;
+    }
+
+    public Integer getCourseId() {
+        return courseId;
+    }
+
+    public void setCourseId(Integer courseId) {
+        this.courseId = courseId;
+    }
+
+    public String getCourseName() {
+        return courseName;
+    }
+
+    public void setCourseName(String courseName) {
+        this.courseName = courseName;
+    }
+
+    @Override
+    public Course clone() {
+        try {
+            return (Course) super.clone();
+        } catch (CloneNotSupportedException e) {
+            throw new AssertionError();
+        }
+    }
+}

core-java-modules/core-java-lang-oop-patterns/src/main/java/com/baeldung/deepcopyarraylist/Student.java

@@ -0,0 +1,103 @@
+package com.baeldung.deepcopyarraylist;
+
+import java.io.Serializable;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.apache.commons.lang3.SerializationUtils;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+public class Student implements Serializable, Cloneable {
+
+    private int studentId;
+    private String studentName;
+    private Course course;
+
+    public Student() {
+    }
+
+    public Student(int studentId, String studentName, Course course) {
+        this.studentId = studentId;
+        this.studentName = studentName;
+        this.course = course;
+    }
+
+    public Student(Student student) {
+        this.studentId = student.getStudentId();
+        this.studentName = student.getStudentName();
+        this.course = new Course(student.getCourse()
+            .getCourseId(), student.getCourse()
+            .getCourseName());
+    }
+
+    public static Student createDeepCopy(Student student) {
+        ObjectMapper objectMapper = new ObjectMapper();
+        try {
+            return objectMapper.readValue(objectMapper.writeValueAsString(student), Student.class);
+        } catch (JsonProcessingException e) {
+            throw new IllegalArgumentException(e);
+        }
+    }
+
+    public static List<Student> deepCopyUsingJackson(List<Student> students) {
+        return students.stream()
+            .map(Student::createDeepCopy)
+            .collect(Collectors.toList());
+    }
+
+    public static List<Student> deepCopyUsingCloneable(List<Student> students) {
+        return students.stream()
+            .map(Student::clone)
+            .collect(Collectors.toList());
+    }
+
+    public static List<Student> deepCopyUsingCopyConstructor(List<Student> students) {
+        return students.stream()
+            .map(Student::new)
+            .collect(Collectors.toList());
+    }
+
+    public static List<Student> deepCopyUsingSerialization(List<Student> students) {
+        return students.stream()
+            .map(SerializationUtils::clone)
+            .collect(Collectors.toList());
+    }
+
+    public int getStudentId() {
+        return studentId;
+    }
+
+    public void setStudentId(int studentId) {
+        this.studentId = studentId;
+    }
+
+    public String getStudentName() {
+        return studentName;
+    }
+
+    public void setStudentName(String studentName) {
+        this.studentName = studentName;
+    }
+
+    public Course getCourse() {
+        return course;
+    }
+
+    public void setCourse(Course course) {
+        this.course = course;
+    }
+
+    @Override
+    public Student clone() {
+        Student student;
+        try {
+            student = (Student) super.clone();
+        } catch (CloneNotSupportedException e) {
+            throw new AssertionError();
+        }
+        student.course = this.course.clone();
+        return student;
+    }
+}

core-java-modules/core-java-lang-oop-patterns/src/test/java/com/baeldung/deepcopyarraylist/DeepCopyArrayListUnitTest.java

@@ -0,0 +1,77 @@
+package com.baeldung.deepcopyarraylist;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.Test;
+import org.junit.jupiter.api.Assertions;
+
+public class DeepCopyArrayListUnitTest {
+
+    @Test
+    public void whenCreatingCopyWithCloneable_thenObjectsShouldNotBeSame() {
+        Course course = new Course(1, "Spring Masterclass");
+        Student student1 = new Student(1, "John", course);
+        Student student2 = new Student(2, "David", course);
+        List<Student> students = new ArrayList<>();
+        students.add(student1);
+        students.add(student2);
+
+        List<Student> deepCopy = Student.deepCopyUsingCloneable(students);
+
+        Assertions.assertNotEquals(students.get(0), deepCopy.get(0));
+        Assertions.assertNotEquals(students.get(1), deepCopy.get(1));
+
+    }
+
+    @Test
+    public void whenCreatingDeepCopyWithCopyConstructor_thenObjectsShouldNotBeSame() {
+
+        Course course = new Course(1, "Spring Masterclass");
+        Student student1 = new Student(1, "John", course);
+        Student student2 = new Student(2, "David", course);
+
+        List<Student> students = new ArrayList<>();
+        students.add(student1);
+        students.add(student2);
+
+        List<Student> deepCopy = Student.deepCopyUsingCopyConstructor(students);
+
+        Assertions.assertNotEquals(students.get(0), deepCopy.get(0));
+        Assertions.assertNotEquals(students.get(1), deepCopy.get(1));
+    }
+
+    @Test
+    public void whenCreatingDeepCopyWithSerializationUtils_thenObjectsShouldNotBeSame() {
+
+        Course course = new Course(1, "Spring Masterclass");
+        Student student1 = new Student(1, "John", course);
+        Student student2 = new Student(2, "David", course);
+
+        List<Student> students = new ArrayList<>();
+        students.add(student1);
+        students.add(student2);
+
+        List<Student> deepCopy = Student.deepCopyUsingSerialization(students);
+
+        Assertions.assertNotEquals(students.get(0), deepCopy.get(0));
+        Assertions.assertNotEquals(students.get(1), deepCopy.get(1));
+    }
+
+    @Test
+    public void whenCreatingDeepCopyWithJackson_thenObjectsShouldNotBeSame() {
+
+        Course course = new Course(1, "Spring Masterclass");
+        Student student1 = new Student(1, "John", course);
+        Student student2 = new Student(2, "David", course);
+
+        List<Student> students = new ArrayList<>();
+        students.add(student1);
+        students.add(student2);
+
+        List<Student> deepCopy = Student.deepCopyUsingJackson(students);
+
+        Assertions.assertNotEquals(students.get(0), deepCopy.get(0));
+        Assertions.assertNotEquals(students.get(1), deepCopy.get(1));
+    }
+}