Add complete codes for an article about deep copy (#3610)

* Add complete codes for an article about deep copy

* Add missing gson dependency

* Apply changes suggested in PR comments

* Apply changes suggested in PR comments

* Apply changes suggested in PR comments

core-java/pom.xml

@@ -78,6 +78,11 @@
             <artifactId>jackson-databind</artifactId>
             <version>${jackson.version}</version>
         </dependency>
+        <dependency>
+            <groupId>com.google.code.gson</groupId>
+            <artifactId>gson</artifactId>
+            <version>${gson.version}</version>
+        </dependency>
 
         <!-- logging -->
         <dependency>
@@ -468,6 +473,7 @@
     <properties>
         <!-- marshalling -->
         <jackson.version>2.8.5</jackson.version>
+        <gson.version>2.8.2</gson.version>
 
         <!-- logging -->
         <org.slf4j.version>1.7.21</org.slf4j.version>

core-java/src/main/java/com/baeldung/deepcopy/Address.java

@@ -0,0 +1,59 @@
+package com.baeldung.deepcopy;
+
+import java.io.Serializable;
+
+public class Address implements Serializable, Cloneable {
+
+    @Override
+    public Object clone() {
+        try {
+            return (Address) super.clone();
+        } catch (CloneNotSupportedException e) {
+            return new Address(this.street, this.getCity(), this.getCountry());
+        }
+    }
+
+    private static final long serialVersionUID = 1740913841244949416L;
+    private String street;
+    private String city;
+
+    private String country;
+
+    public Address(Address that) {
+        this(that.getStreet(), that.getCity(), that.getCountry());
+    }
+
+    public Address(String street, String city, String country) {
+        this.street = street;
+        this.city = city;
+        this.country = country;
+    }
+
+    public Address() {
+    }
+
+    public String getStreet() {
+        return street;
+    }
+
+    public String getCity() {
+        return city;
+    }
+
+    public String getCountry() {
+        return country;
+    }
+
+    public void setStreet(String street) {
+        this.street = street;
+    }
+
+    public void setCity(String city) {
+        this.city = city;
+    }
+
+    public void setCountry(String country) {
+        this.country = country;
+    }
+}
+

core-java/src/main/java/com/baeldung/deepcopy/User.java

@@ -0,0 +1,48 @@
+package com.baeldung.deepcopy;
+
+import java.io.Serializable;
+
+public class User implements Serializable, Cloneable {
+
+    private static final long serialVersionUID = -3427002229954777557L;
+    private String firstName;
+    private String lastName;
+    private Address address;
+
+    public User(String firstName, String lastName, Address address) {
+        this.firstName = firstName;
+        this.lastName = lastName;
+        this.address = address;
+    }
+
+    public User(User that) {
+        this(that.getFirstName(), that.getLastName(), new Address(that.getAddress()));
+    }
+
+    public User() {
+    }
+
+    @Override
+    public Object clone() {
+        User user;
+        try {
+            user = (User) super.clone();
+        } catch (CloneNotSupportedException e) {
+            user = new User(this.getFirstName(), this.getLastName(), this.getAddress());
+        }
+        user.address = (Address) this.address.clone();
+        return user;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public Address getAddress() {
+        return address;
+    }
+}

core-java/src/test/java/com/baeldung/deepcopy/DeepCopyUnitTest.java

@@ -0,0 +1,128 @@
+package com.baeldung.deepcopy;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.IOException;
+
+import org.apache.commons.lang.SerializationUtils;
+import org.junit.Ignore;
+import org.junit.Test;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.google.gson.Gson;
+
+public class DeepCopyUnitTest {
+
+    @Test
+    public void whenCreatingDeepCopyWithCopyConstructor_thenObjectsShouldNotBeSame() {
+
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+
+        User deepCopy = new User(pm);
+
+        assertThat(deepCopy).isNotSameAs(pm);
+    }
+
+    @Test
+    public void whenModifyingOriginalObject_thenConstructorCopyShouldNotChange() {
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+        User deepCopy = new User(pm);
+
+        address.setCountry("Great Britain");
+
+        assertThat(deepCopy.getAddress().getCountry()).isNotEqualTo(pm.getAddress().getCountry());
+    }
+
+    @Test
+    public void whenModifyingOriginalObject_thenCloneCopyShouldNotChange() {
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+        User deepCopy = (User) pm.clone();
+
+        address.setCountry("Great Britain");
+
+        assertThat(deepCopy.getAddress().getCountry()).isNotEqualTo(pm.getAddress().getCountry());
+    }
+
+    @Test
+    public void whenModifyingOriginalObject_thenCommonsCloneShouldNotChange() {
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+        User deepCopy = (User) SerializationUtils.clone(pm);
+
+        address.setCountry("Great Britain");
+
+        assertThat(deepCopy.getAddress().getCountry()).isNotEqualTo(pm.getAddress().getCountry());
+    }
+
+    @Test
+    public void whenModifyingOriginalObject_thenGsonCloneShouldNotChange() {
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+        Gson gson = new Gson();
+        User deepCopy = gson.fromJson(gson.toJson(pm), User.class);
+
+        address.setCountry("Great Britain");
+
+        assertThat(deepCopy.getAddress().getCountry()).isNotEqualTo(pm.getAddress().getCountry());
+    }
+
+    @Test
+    public void whenModifyingOriginalObject_thenJacksonCopyShouldNotChange() throws IOException {
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+        ObjectMapper objectMapper = new ObjectMapper();
+        User deepCopy = objectMapper.readValue(objectMapper.writeValueAsString(pm), User.class);
+
+        address.setCountry("Great Britain");
+
+        assertThat(deepCopy.getAddress().getCountry()).isNotEqualTo(pm.getAddress().getCountry());
+    }
+
+    @Test
+    @Ignore
+    public void whenMakingCopies_thenShowHowLongEachMethodTakes() throws CloneNotSupportedException, IOException {
+        int times = 1000000;
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+
+        long start = System.currentTimeMillis();
+        for (int i = 0; i < times; i++) {
+            User primeMinisterClone = (User) SerializationUtils.clone(pm);
+        }
+        long end = System.currentTimeMillis();
+        System.out.println("Cloning with Apache Commons Lang took " + (end - start) + " milliseconds.");
+
+        start = System.currentTimeMillis();
+        Gson gson = new Gson();
+        for (int i = 0; i < times; i++) {
+            User primeMinisterClone = gson.fromJson(gson.toJson(pm), User.class);
+        }
+        end = System.currentTimeMillis();
+        System.out.println("Cloning with Gson took " + (end - start) + " milliseconds.");
+
+        start = System.currentTimeMillis();
+        for (int i = 0; i < times; i++) {
+            User primeMinisterClone = new User(pm);
+        }
+        end = System.currentTimeMillis();
+        System.out.println("Cloning with the copy constructor took " + (end - start) + " milliseconds.");
+
+        start = System.currentTimeMillis();
+        for (int i = 0; i < times; i++) {
+            User primeMinisterClone = (User) pm.clone();
+        }
+        end = System.currentTimeMillis();
+        System.out.println("Cloning with Cloneable interface took " + (end - start) + " milliseconds.");
+
+        start = System.currentTimeMillis();
+        ObjectMapper objectMapper = new ObjectMapper();
+        for (int i = 0; i < times; i++) {
+            User primeMinisterClone = objectMapper.readValue(objectMapper.writeValueAsString(pm), User.class);
+        }
+        end = System.currentTimeMillis();
+        System.out.println("Cloning with Jackson took " + (end - start) + " milliseconds.");
+    }
+}

core-java/src/test/java/com/baeldung/deepcopy/ShallowCopyUnitTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.deepcopy;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class ShallowCopyUnitTest {
+
+
+    @Test
+    public void whenShallowCopying_thenObjectsShouldNotBeSame() {
+
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+
+        User shallowCopy = new User(pm.getFirstName(), pm.getLastName(), pm.getAddress());
+
+        assertThat(shallowCopy)
+                .isNotSameAs(pm);
+    }
+
+    @Test
+    public void whenModifyingOriginalObject_thenCopyShouldChange() {
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+        User shallowCopy = new User(pm.getFirstName(), pm.getLastName(), pm.getAddress());
+
+        address.setCountry("Great Britain");
+        
+        assertThat(shallowCopy.getAddress().getCountry())
+                .isEqualTo(pm.getAddress().getCountry());
+    }
+}