Deep copy and Shallow copy in java

Shallow Copy:

A new object will be created that has an exact copy values of its original object. Means, it will copy all of the fields , suppose if any of the fields are object reference then reference address only will be copied. That is, reference address means, memory address.

Before shallow copy picture 1

Before Shallow Copy

After Shallow copy picture 2

                                                             After Shallow Copy

We have added here two pics, and first picture mentioning before shallow copy and second picture is after doing shallow copy. Now lets see points,

1. Initially Main object 1 have filed 1 and contain object 1.
2. After doing shallow copy Main Object 2 is created with filed 2.
3. But still contain object 2 is not created and Main object 2 is pointing contain object 1. Means, memory address copied. (reference address).
4. So if you will do any changes in Contain object 1 of Main object 1, it will reflect in Main object 2 also.

Deep copy

It will copy all of the fields and all the dynamically allocated memory address pointed by that object are also copied.  Below picture will say clearly.

Before Deep Copy

After Deep copy

We have added here two pics, and first picture mentioning before deep copy and second picture is after doing deep copy. Now lets see points,

1. Initially Main object 1 have filed 1 and contain object 1.
2. After doing deep copy Main Object 2 is created with filed 2 and contain object 2.
3. Remember here, contain object 2 was not created in shallow, but in deep contain object 2 is created.
4. So if you will do any changes in Contain object 1 of Main object 1, it will not reflect in Main object 2 .

Shallow copy with example code

 

public class Subject {

 private String name;

 public String getName() {
  return name;
 }

 public void setName(String name) {
  this.name = name;
 }

 public Subject(String name) {
  this.name = name;
 }
}

Create another one class called Student and code is below

public class Student implements Cloneable {

 // Contained object
 private Subject subj;
 private String name;

 
 public Subject getSubj() {
  return subj;
 }

 
 public void setSubj(Subject subj) {
  this.subj = subj;
 }

 public String getName() {
  return name;
 }

 
 public void setName(String name) {
  this.name = name;
 }

 public Student(String name, String sub) {
  this.name = name;
  this.subj = new Subject(sub);
 }

 public Object clone() {
  // Create shallow copy
  try {
   return super.clone();
  } catch (CloneNotSupportedException e) {
   return null;
  }
 }
}

Below class is to test shallow copy

public class ShallowTest {

 public static void main(String[] args) {
  // Original Object
  Student stud = new Student("RAJA", "MATHS");
  System.out.println("Original Object : " + stud.getName() + " ---- "
    + stud.getSubj().getName());
  // Create Clone Object
  Student clonedStud = (Student) stud.clone();
  System.out.println("After Cloned Object: " + clonedStud.getName() + " ---- "
    + clonedStud.getSubj().getName());
  //Again setting new data
  stud.setName("Kumar");
  stud.getSubj().setName("CHEMISTRY");
  System.out.println("Original Object after updating: "
    + stud.getName() + " ---- " + stud.getSubj().getName());
  System.out.println("Cloned Object after updating original object: "
      + clonedStud.getName() + " ---- "
      + clonedStud.getSubj().getName());

 }

}

Output

Original Object : RAJA ---- MATHS
After Cloned Object: RAJA ---- MATHS
Original Object after updating : Kumar ---- CHEMISTRY
Cloned Object after updating original object: RAJA - CHEMISTRY

Deep copy with example code

You can use the above shallow example and do a Little bit change like below and execute it. 

public class Student implements Cloneable {

 // Contained object
 private Subject subj;
 private String name;

 
 public Subject getSubj() {
  return subj;
 }

 
 public void setSubj(Subject subj) {
  this.subj = subj;
 }

 
 public String getName() {
  return name;
 }

 
 public void setName(String name) {
  this.name = name;
 }

 public Student(String name, String sub) {
  this.name = name;
  this.subj = new Subject(sub);
 }

 public Object clone() {
  // For deep copy
  Student student = new Student(name, subj.getName());
  return student;
 }

}

The only difference here, we are creating new object inside clone method and returning.