Found 2620 Articles for Java

Hash set and tree set both belong to the collection framework. HashSet is the implementation of the Set interface whereas Tree set implements sorted set. Tree set is backed by TreeMap while HashSet is backed by a hashmap.Sr. No.KeyHash SetTree Set1Implementation Hash set is implemented using HashTable The tree set is implemented using a tree structure. 2Null Object HashSet allows a null object The tree set does not allow the null object. It throws the null pointer exception. 3Methods Hash set use equals method to compare two objects Tree set use compare method for comparing two objects. 4Heterogeneous object Hash set doesn't now allow a heterogeneous object Tree set allows a ... Read More

Iterator and Enumeration both are the cursors to traverse and access an element from the collection. They both belong to the collection framework. Enumeration was added in JDK1.0 and Iterator in the JDK.1.2 version in the collection framework. Enumeration can’t make structural changes in the collection because it has read-only access to the element in the collection. It has the following methods :*hasMoreElements()*nextElement()On the other hand, an iterator can read and remove the element in the collection. It has the following methods −*hasNext()*next()*remove()Sr. No.KeyIteratorEnumeration1BasicIn Iterator,  we can read and remove element while traversing element in the collections. Using Enumeration, we can only ... Read More

Save and saveAndFlush both can be used for saving entities. They both are both belong to the Spring data library. save may or may not write your changes to the DB straight away. When we call saveAndFlush system are enforcing the synchronization of your model state with the DB.Sr. No.KeySaveSaveAndFlush1RepositoryIt belongs to CrudRepositoryIt belongs to JPARepository2Data flush StrategyIt doesn't flush data directly to a database until and unless we explicitly call flush and commit method.It's flush directly flush data to a database.3Bulk SaveCrudRepository provides bulk save methodsaveAndFlush method doesn't support the bulk operation 4Data Visibility after savingIt doesn't flush data directly ... Read More

CrudRepository and JPA repository both are the interface of the spring data repository library. Spring data repository reduces the boilerplate code by providing some predefined finders to access the data layer for various persistence layers.JPA repository extends CrudRepository and PagingAndSorting repository. It inherits some finders from crud repository such as findOne, gets and removes an entity. It also provides some extra methods related to JPA such as delete records in batch, flushing data directly to a database base and methods related to pagination and sorting.We need to extend this repository in our application and then we can access all methods ... Read More

The @JsonUnwrapped annotation can be used to unwrap values during the serialization and deserialization process. It helps to render the values of a composed class as if it belongs to the parent class.Syntax@Target(value={ANNOTATION_TYPE, FIELD, METHOD, PARAMETER}) @Retention(value=RUNTIME) public @interface JsonUnwrappedExampleimport com.fasterxml.jackson.annotation.JsonUnwrapped; import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.core.JsonProcessingException; public class JsonUnwrappedAnnotationTest {    public static void main(String args[]) throws JsonProcessingException {       ObjectMapper mapper = new ObjectMapper();       String jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(new Employee());       System.out.println(jsonString);    } } class Employee {    public int empId = 110;    public String empName = "Raja Ramesh";    @JsonUnwrapped   ... Read More

The @JsonValue annotation is useful at the method level. We can use this annotation to generate a JSON string from java object. If we want to print a serialized object then override the toString() method. But using @JsonValue annotation, we can define a way in which java object is serialized.Syntax@Target(value={ANNOTATION_TYPE, METHOD, FIELD}) @Retention(value=RUNTIME) public @interface JsonValueExampleimport com.fasterxml.jackson.annotation.JsonProperty; import com.fasterxml.jackson.annotation.JsonValue; import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.databind.ObjectMapper; import java.io.IOException; public class JsonValueAnnotationTest {    public static void main(String args[]) throws Exception {       ObjectMapper mapper = new ObjectMapper();       String jsonString = mapper.writeValueAsString(new Student());       System.out.println(jsonString);    } } ... Read More

The @JSON annotation is used by JSONSerializer class to exclude or include a field during the serialization process. We can use the serialize() method of JSONSerializer class to perform a shallow serialization of the target instance.Syntax@Retention(value=RUNTIME) @Target(value={FIELD, TYPE, METHOD}) public @interface JSONExampleimport flexjson.JSONSerializer; import flexjson.JSON; public class JSONAnnotationTest {    public static void main(String[] args) {       JSONSerializer serializer = new JSONSerializer().prettyPrint(true);       Employee emp = new Employee("Raja", "Ramesh", 30, "Hyderabad");       String jsonStr = serializer.serialize(emp);       System.out.println(jsonStr);    } } // Employee class class Employee {    private String firstName, lastName, address;    private ... Read More

The @JsonDeserialize annotation is used to declare custom deserializer while deserializing JSON to Java object. We can implement a  custom deserializer by extending the StdDeserializer class with a generic type Employee and need to override the deserialize() method of StdDeserializer class.Syntax@Target(value={ANNOTATION_TYPE, METHOD, FIELD, TYPE, PARAMETER}) @Retention(value=RUNTIME) public @interface JsonDeserializeIn the below program, we can implement a custom deserializer using @JsonDeserialize annotationExampleimport java.io.*; import com.fasterxml.jackson.core.*; import com.fasterxml.jackson.databind.*; import com.fasterxml.jackson.databind.annotation.*; import com.fasterxml.jackson.databind.deser.std.*; public class JsonDeSerializeAnnotationTest {    public static void main (String[] args) throws JsonProcessingException, IOException {       Employee emp = new Employee(115, "Adithya");       ObjectMapper mapper = new ObjectMapper();     ... Read More

The @JsonSerialize annotation is used to declare custom serializer during the serialization of a field. We can implement a custom serializer by extending the StdSeralizer class. and need to override the serialize() method of StdSerializer class.Syntax@Target(value={ANNOTATION_TYPE, METHOD, FIELD, TYPE, PARAMETER}) @Retention(value=RUNTIME) public @interface JsonSerializeIn the below program, we can implement a custom serializer using @JsonSerialize annotationExampleimport java.io.*; import com.fasterxml.jackson.core.*; import com.fasterxml.jackson.databind.*; import com.fasterxml.jackson.databind.annotation.*; import com.fasterxml.jackson.databind.ser.std.*; public class JsonSerializeAnnotationTest {    public static void main (String[] args) throws JsonProcessingException, IOException {       Employee emp = new Employee(115, "Adithya", new String[] {"Java", "Python", "Scala"});       ObjectMapper mapper = new ... Read More

The JSON-lib API is a java library to serialize and de-serialize java beans, maps, arrays, and collections in the JSON format. We need to convert a JSON string to a bean by converting a string to JSON object first then convert this to a java bean.Syntaxpublic static Object toBean(JSONObject jsonObject, Class beanClass)In the below program, we can convert a JSON string to a bean.Exampleimport net.sf.json.JSONObject; import net.sf.json.JSONSerializer; public class ConvertJSONStringToBeanTest {    public static void main(String[] args) {       String jsonStr = "{\"firstName\": \"Adithya\", \"lastName\": \"Sai\", \"age\": 30, \"technology\": \"Java\"}";       JSONObject jsonObj = (JSONObject)JSONSerializer.toJSON(jsonStr); // convert String ... Read More