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Deepcopy: Difference between revisions
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Another possible exception would be classes and objects (which are not values but collections of references to values). But as a general rule copying of an object should be delegated to the object itself rather than imposed from the outside. Also, "deepcopy" violates the Law of Demeter as well as the concept of black-box reuse -- if you need deepcopy in J, you probably should not be representing your data structure as objects.
=={{header|Java}}==
Deep copy can be performed several ways.
<ol>
<li>Immutable Objects. Do not perform the deep copy, use immutable objects. If an object is immutable, and hence unchangeable, then a deep copy is not needed. However, this task is about deep copy, so we will continue with the demonstration.</li>
<li>Copy Constructor. Use a copy constructor to make a duplicate of the object. This is not a feature of Java, but a design pattern.</li>
<li>Object Serialization. Java supports serialization of an object to a byte stream using the <code>Serializable</code> interface. However, there are security concerns with this methodology. See the various Internet articles.</li>
<li>Object Clone. Java supports cloning of an object using the <code>Cloneable</code> interface. As with serialization, there are security concerns with this methodology. See the various Internet articles.</li>
</ol>
Copy constructor, object serialization, and object clone are demonstrated below.
<lang java>
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
public class DeepCopy {
public static void main(String[] args) {
Person p1 = new Person("Clark", "Kent", new Address("1 World Center", "Metropolis", "NY", "010101"));
Person p2 = p1;
System.out.printf("Demonstrate shallow copy. Both are the same object.%n");
System.out.printf("Person p1 = %s%n", p1);
System.out.printf("Person p2 = %s%n", p2);
System.out.printf("Set city on person 2. City on both objects is changed.%n");
p2.getAddress().setCity("New York");
System.out.printf("Person p1 = %s%n", p1);
System.out.printf("Person p2 = %s%n", p2);
p1 = new Person("Clark", "Kent", new Address("1 World Center", "Metropolis", "NY", "010101"));
p2 = new Person(p1);
System.out.printf("%nDemonstrate copy constructor. Object p2 is a deep copy of p1.%n");
System.out.printf("Person p1 = %s%n", p1);
System.out.printf("Person p2 = %s%n", p2);
System.out.printf("Set city on person 2. City on objects is different.%n");
p2.getAddress().setCity("New York");
System.out.printf("Person p1 = %s%n", p1);
System.out.printf("Person p2 = %s%n", p2);
p2 = (Person) deepCopy(p1);
System.out.printf("%nDemonstrate serialization. Object p2 is a deep copy of p1.%n");
System.out.printf("Person p1 = %s%n", p1);
System.out.printf("Person p2 = %s%n", p2);
System.out.printf("Set city on person 2. City on objects is different.%n");
p2.getAddress().setCity("New York");
System.out.printf("Person p1 = %s%n", p1);
System.out.printf("Person p2 = %s%n", p2);
p2 = (Person) p1.clone();
System.out.printf("%nDemonstrate cloning. Object p2 is a deep copy of p1.%n");
System.out.printf("Person p1 = %s%n", p1);
System.out.printf("Person p2 = %s%n", p2);
System.out.printf("Set city on person 2. City on objects is different.%n");
p2.getAddress().setCity("New York");
System.out.printf("Person p1 = %s%n", p1);
System.out.printf("Person p2 = %s%n", p2);
}
/**
* Makes a deep copy of any Java object that is passed.
*/
private static Object deepCopy(Object object) {
try {
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
ObjectOutputStream outputStrm = new ObjectOutputStream(outputStream);
outputStrm.writeObject(object);
ByteArrayInputStream inputStream = new ByteArrayInputStream(outputStream.toByteArray());
ObjectInputStream objInputStream = new ObjectInputStream(inputStream);
return objInputStream.readObject();
}
catch (Exception e) {
e.printStackTrace();
return null;
}
}
public static class Address implements Serializable, Cloneable {
private static final long serialVersionUID = -7073778041809445593L;
private String street;
private String city;
private String state;
private String postalCode;
public String getStreet() {
return street;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getState() {
return state;
}
public String getPostalCode() {
return postalCode;
}
@Override
public String toString() {
return "[street=" + street + ", city=" + city + ", state=" + state + ", code=" + postalCode + "]";
}
public Address(String s, String c, String st, String p) {
street = s;
city = c;
state = st;
postalCode = p;
}
// Copy constructor
public Address(Address add) {
street = add.street;
city = add.city;
state = add.state;
postalCode = add.postalCode;
}
// Support Cloneable
@Override
public Object clone() {
return new Address(this);
}
}
public static class Person implements Serializable, Cloneable {
private static final long serialVersionUID = -521810583786595050L;
private String firstName;
private String lastName;
private Address address;
public String getFirstName() {
return firstName;
}
public String getLastName() {
return lastName;
}
public Address getAddress() {
return address;
}
@Override
public String toString() {
return "[first name=" + firstName + ", last name=" + lastName + ", address=" + address + "]";
}
public Person(String fn, String ln, Address add) {
firstName = fn;
lastName = ln;
address = add;
}
// Copy Constructor
public Person(Person person) {
firstName = person.firstName;
lastName = person.lastName;
address = new Address(person.address); // Invoke copy constructor of mutable sub-objects.
}
// Support Cloneable
@Override
public Object clone() {
return new Person(this);
}
}
}
</lang>
{{out}}
<pre>
Demonstrate shallow copy. Both are the same object.
Person p1 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=Metropolis, state=NY, code=010101]]
Person p2 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=Metropolis, state=NY, code=010101]]
Set city on person 2. City on both objects is changed.
Person p1 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=New York, state=NY, code=010101]]
Person p2 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=New York, state=NY, code=010101]]
Demonstrate copy constructor. Object p2 is a deep copy of p1.
Person p1 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=Metropolis, state=NY, code=010101]]
Person p2 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=Metropolis, state=NY, code=010101]]
Set city on person 2. City on objects is different.
Person p1 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=Metropolis, state=NY, code=010101]]
Person p2 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=New York, state=NY, code=010101]]
Demonstrate serialization. Object p2 is a deep copy of p1.
Person p1 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=Metropolis, state=NY, code=010101]]
Person p2 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=Metropolis, state=NY, code=010101]]
Set city on person 2. City on objects is different.
Person p1 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=Metropolis, state=NY, code=010101]]
Person p2 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=New York, state=NY, code=010101]]
Demonstrate cloning. Object p2 is a deep copy of p1.
Person p1 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=Metropolis, state=NY, code=010101]]
Person p2 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=Metropolis, state=NY, code=010101]]
Set city on person 2. City on objects is different.
Person p1 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=Metropolis, state=NY, code=010101]]
Person p2 = [first name=Clark, last name=Kent, address=[street=1 World Center, city=New York, state=NY, code=010101]]
</pre>
=={{header|JavaScript}}==
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