Java Articles - Page 155 of 440

The Flexjson is a lightweight library for serializing and deserializing Java objects into and from JSON format. A JSONSerializer is the main class for performing serialization of Java objects to JSON. We can serialize a JSON string to an Output Handler using the WriterOutputHandler class and it implements the OutputHandler interface.Syntaxpublic class WriterOutputHandler extends Object implements OutputHandlerExampleimport java.io.*; import flexjson.JSONSerializer; import flexjson.OutputHandler; import flexjson.WriterOutputHandler; public class JsonOutputHandlerTest {    public static void main(String[] args) {       JSONSerializer serializer = new JSONSerializer().prettyPrint(true); // pretty print JSON       Employee emp = new Employee("Raja", "Ramesh", 28, "Hyderabad");       OutputHandler out = new WriterOutputHandler(new ... Read More

The @JsonProperty annotation can be used to indicate the property name in JSON. This annotation can be used for a constructor or factory method. The @JsonCreator annotation is useful in situations where the @JsonSetter annotation cannot be used. For instance, immutable objects do not have any setter methods, so they need their initial values injected into the constructor.@JsonProperty - ConstructorExampleimport com.fasterxml.jackson.annotation.*; import java.io.IOException; import com.fasterxml.jackson.databind.*; public class JsonCreatorTest1 {    public static void main(String[] args) throws IOException {       ObjectMapper om = new ObjectMapper();       String jsonString = "{\"id\":\"101\", \"fullname\":\"Ravi Chandra\", \"location\":\"Pune\"}";       System.out.println("JSON: " + jsonString);   ... Read More

A JSONObject is an unordered collection of name/value pairs and parses text from a String to produce a map-like object. However, we can auto-increment the property of a JSONObject using the increment() method of JSONObject class. If there is no such property, create one with a value of 1. If there is such a property and if it is an Integer, Long, Double or Float then add one to it.Syntaxpublic JSONObject increment(java.lang.String key) throws JSONExceptionExampleimport org.json.JSONException; import org.json.JSONObject; public class IncrementJSONObjectTest {    public static void main(String[] args) throws JSONException {       JSONObject jsonObj = new JSONObject();       jsonObj.put("year", 2019);     ... Read More

When you have created an array of a particular data type with fixed size and populate it if you store a value other than its datatype an ArrayStoreException is thrown at the run time.ExampleIn the following Java program, we are creating an Integer array and trying to store a double value in it. Live Demoimport java.util.Arrays; public class ArrayStoreExceptionExample {    public static void main(String args[]) {       Number integerArray[] = new Integer[3];       integerArray[0] = 12548;       integerArray[1] = 36987;       integerArray[2] = 555.50;       integerArray[3] = 12548;     ... Read More

No, HashMap does not allow duplicate keys. The HashMap is a class that implements the Map interface. It is based on the Hash table. It is used to store key-value pairs. It allows null keys and values, but it does not allow duplicate keys. You can store key-value pairs in the HashMap object. Once you do so, you can retrieve the values of the respective keys, but the values we use for keys should be unique. Let's understand what will happen if we try to add a duplicate key into a HashMap.Addng a duplicate key to a HashMapThe put() method ... Read More

The ArrayList class in Java is a Resizable-array implementation of the List interface. It allows null values. Java clear() Method V/S removeAll() Method There are some important differences between the clear() and removeAll (Collection c) methods of the ArrayList class. This table compares these two methods. Key clear() removeAll() ... Read More

Jackson is a Java library that is used to convert JSON to Java objects and vice versa. Conversion of JSON to a Java object is called deserialization, and Java object to JSON is known as serialization. Both of these tasks can be done by using the Jackson library. In this article, we are going to learn how to convert JSON to Java objects using the Jackson library. Jackson Library: Convert a JSON to a Java Object The ObjectMapper class belongs to the Jackson library. This class is responsible for the serialization and deserialization of Java objects. The ObjectMapper class is used ... Read More

The Console class is part of the Java.io package and is used to read input from the keyboard or user and write output to the console. Unlike Scanner, the Console class provides methods to read text and passwords. If you read a password using the Console class, it will not be displayed to the user (without showing the typed characters). To use the Console class, we need its object, and the Console object is obtained by calling System.console() as shown below - Console console = System.console(); Note: If you try to execute the program in a non-interactive environment like an IDE, it doesn’t work. It ... Read More

The Flexjson library is a lightweight Java library for serializing and de-serializing java beans, maps, arrays, and collections in a JSON format. A JSONSerializer is the main class for performing serialization of Java objects to JSON and by default performs a shallow serialization. We can wrap a JSON object using the rootName() method of JSONSerializer class, this method wraps the resulting JSON in a javascript object that contains a single field named rootName.Syntaxpublic JSONSerializer rootName(String rootName)Exampleimport flexjson.JSONSerializer; public class JSONRootNameTest {    public static void main(String[] args) {       JSONSerializer serializer = new JSONSerializer().rootName("My_Employee").prettyPrint(true);       Employee emp = new Employee("Adithya", "Jai", 28, ... Read More

No, you cannot change the method signature while overriding. Changing the method signature becomes method overloading, not overriding. Now, let's understand why - Method Signature In Java, a method signature consists of - Method name: It is used to call the method. Parameter list: It includes the number, type, and order of parameters. Note: The method signature does not include return type, ... Read More