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lieshengliesheng
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sample code for article "Java Optional As Return Type"
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‎core-java-modules/core-java-8-2/pom.xml‎

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<artifactId>icu4j</artifactId>
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<version>${icu.version}</version>
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</dependency>
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<dependency>
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<groupId>org.hibernate</groupId>
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<artifactId>hibernate-core</artifactId>
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<version>5.4.0.Final</version>
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</dependency>
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<dependency>
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<groupId>com.h2database</groupId>
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<artifactId>h2</artifactId>
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<version>1.4.197</version>
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</dependency>
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<dependency>
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<groupId>com.fasterxml.jackson.core</groupId>
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<artifactId>jackson-databind</artifactId>
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<version>2.9.8</version>
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</dependency>
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</dependencies>
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<build>

‎core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/HandleOptionalTypeExample.java‎

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package com.baeldung.optionalReturnType;
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import java.util.HashMap;
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import java.util.Map;
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import java.util.Optional;
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public class HandleOptionalTypeExample {
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static Map<String, User> usersByName = new HashMap();
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static {
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User user1 = new User();
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user1.setUserId(1l);
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user1.setFirstName("baeldung");
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usersByName.put("baeldung", user1);
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}
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public static void main(String[] args) {
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changeUserName("baeldung", "baeldung-new");
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changeUserName("user", "user-new");
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}
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public static void changeUserName(String oldFirstName, String newFirstName) {
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Optional<User> userOpt = findUserByName(oldFirstName);
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if(userOpt.isPresent()){
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User user = userOpt.get();
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user.setFirstName(newFirstName);
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System.out.println("user with name "+oldFirstName+" is changed to "+ user.getFirstName());
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} else {
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//user is missing
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System.out.println("user with name "+oldFirstName+" is not found.");
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}
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}
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public static Optional<User> findUserByName(String name){
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//look up the user in the database, the user object below could be null
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User user=usersByName.get(name);
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Optional<User> opt = Optional.ofNullable(user);
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return opt;
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}
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}

‎core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/OptionalToJsonExample.java‎

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package com.baeldung.optionalReturnType;
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import com.fasterxml.jackson.core.JsonProcessingException;
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import com.fasterxml.jackson.databind.ObjectMapper;
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public class OptionalToJsonExample {
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public static void main(String[] args) {
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UserOptional user = new UserOptional();
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user.setUserId(1l);
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user.setFirstName("Bael Dung");
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ObjectMapper om = new ObjectMapper();
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try {
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System.out.print("user in json is:"+om.writeValueAsString(user));
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} catch (JsonProcessingException e) {
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// TODO Auto-generated catch block
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e.printStackTrace();
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}
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}
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}

‎core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/PersistOptionalTypeExample.java‎

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package com.baeldung.optionalReturnType;
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import java.util.Optional;
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import javax.persistence.EntityManager;
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import javax.persistence.EntityManagerFactory;
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import javax.persistence.Persistence;
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public class PersistOptionalTypeExample {
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static String persistenceUnit = "com.baeldung.optionalReturnType";
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static EntityManagerFactory emf = Persistence.createEntityManagerFactory(persistenceUnit);
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static EntityManager entityManager = emf.createEntityManager();
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public static void main(String[] args) {
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UserOptionalField user1 = new UserOptionalField();
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user1.setUserId(1l);
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user1.setFirstName(Optional.of("Bael Dung"));
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entityManager.persist(user1);
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UserOptional user2 = entityManager.find(UserOptional.class, 1l);
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System.out.print("User2.firstName:"+user2.getFirstName());
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}
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}

‎core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/PersistOptionalTypeExample2.java‎

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package com.baeldung.optionalReturnType;
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import javax.persistence.EntityManager;
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import javax.persistence.EntityManagerFactory;
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import javax.persistence.Persistence;
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public class PersistOptionalTypeExample2 {
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static String persistenceUnit = "com.baeldung.optionalReturnType";
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static EntityManagerFactory emf = Persistence.createEntityManagerFactory(persistenceUnit);
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static EntityManager em = emf.createEntityManager();
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public static void main(String[] args) {
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UserOptional user1 = new UserOptional();
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user1.setUserId(1l);
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user1.setFirstName("Bael Dung");
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em.persist(user1);
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UserOptional user2 = em.find(UserOptional.class, 1l);
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System.out.print("User2.firstName:"+user2.getFirstName());
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}
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}

‎core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/PersistUserNoOptionalExample.java‎

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package com.baeldung.optionalReturnType;
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import javax.persistence.EntityManager;
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import javax.persistence.EntityManagerFactory;
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import javax.persistence.Persistence;
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public class PersistUserNoOptionalExample {
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static String persistenceUnit = "com.baeldung.optionalReturnType";
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static EntityManagerFactory emf = Persistence.createEntityManagerFactory(persistenceUnit);
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static EntityManager em = emf.createEntityManager();
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public static void main(String[] args) {
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User user1 = new User();
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user1.setUserId(1l);
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user1.setFirstName("Bael Dung");
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em.persist(user1);
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User user2 = em.find(User.class, 1l);
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System.out.print("User2.firstName:"+user2.getFirstName());
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}
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}

‎core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/SerializeOptionalTypeExample.java‎

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package com.baeldung.optionalReturnType;
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import java.io.FileOutputStream;
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import java.io.IOException;
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import java.io.ObjectOutputStream;
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import java.util.Optional;
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public class SerializeOptionalTypeExample {
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public static void main(String[] args) {
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User user1 = new User();
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user1.setUserId(1l);
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user1.setFirstName("baeldung");
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serializeObject(user1, "user1.ser");
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UserOptionalField user2 = new UserOptionalField();
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user2.setUserId(1l);
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user2.setFirstName(Optional.of("baeldung"));
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serializeObject(user2, "user2.ser");
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}
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public static void serializeObject(Object object, String fileName) {
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// Serialization
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try {
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FileOutputStream file = new FileOutputStream(fileName);
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ObjectOutputStream out = new ObjectOutputStream(file);
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out.writeObject(object);
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out.close();
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file.close();
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System.out.println("Object "+object.toString()+ " has been serialized to file "+fileName);
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} catch(IOException e) {
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e.printStackTrace();
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}
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}
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}

‎core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/User.java‎

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package com.baeldung.optionalReturnType;
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import java.io.Serializable;
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import javax.persistence.Entity;
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import javax.persistence.Id;
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@Entity
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public class User implements Serializable {
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@Id
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private long userId;
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private String firstName;
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public long getUserId() {
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return userId;
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}
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public void setUserId(long userId) {
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this.userId = userId;
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}
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public String getFirstName() {
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return firstName;
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}
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public void setFirstName(String firstName) {
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this.firstName = firstName;
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}
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}

‎core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/UserOptional.java‎

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package com.baeldung.optionalReturnType;
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import java.io.Serializable;
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import java.util.Optional;
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import javax.persistence.Column;
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import javax.persistence.Entity;
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import javax.persistence.Id;
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@Entity
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public class UserOptional implements Serializable {
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@Id
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private long userId;
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@Column(nullable = true)
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private String firstName;
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public long getUserId() {
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return userId;
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}
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public void setUserId(long userId) {
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this.userId = userId;
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}
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public Optional<String> getFirstName() {
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return Optional.ofNullable(firstName);
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}
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public void setFirstName(String firstName) {
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this.firstName = firstName;
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Optional.ofNullable(firstName);
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}
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}

‎core-java-modules/core-java-8-2/src/main/java/com/baeldung/optionalReturnType/UserOptionalField.java‎

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package com.baeldung.optionalReturnType;
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import java.io.Serializable;
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import java.util.Optional;
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import javax.persistence.Entity;
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import javax.persistence.Id;
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@Entity
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public class UserOptionalField implements Serializable {
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@Id
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private long userId;
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private Optional<String> firstName;
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public long getUserId() {
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return userId;
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}
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public void setUserId(long userId) {
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this.userId = userId;
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}
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public Optional<String> getFirstName() {
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return firstName;
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}
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public void setFirstName(Optional<String> firstName) {
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this.firstName = firstName;
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}
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}

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