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Object Oriented Programming Articles
Page 490 of 589
How can we sort a JSONObject in Java?
A JSONObject is an unordered collection of a key, value pairs, and the values can be any of these types like Boolean, JSONArray, JSONObject, Number and String. The constructor of a JSONObject can be used to convert an external form JSON text into an internal form whose values can be retrieved with the get() and opt() methods or to convert values into a JSON text using the put() and toString() methods.In the below example, we can sort the values of a JSONObject in the descending order.Exampleimport org.json.*; import java.util.*; public class JSonObjectSortingTest { public static void main(String[] ...
Read MoreHow to access the private methods of a class from outside of the class in Java?
You can access the private methods of a class using java reflection package.Step1 − Instantiate the Method class of the java.lang.reflect package by passing the method name of the method which is declared private.Step2 − Set the method accessible by passing value true to the setAccessible() method.Step3 − Finally, invoke the method using the invoke() method.Exampleimport java.lang.reflect.Method; public class DemoTest { private void sampleMethod() { System.out.println("hello"); } } public class SampleTest { public static void main(String args[]) throws Exception { Class c = Class.forName("DemoTest"); Object obj = c.newInstance(); ...
Read MoreHow many ways can get the instance of a Class class in Java?
You can create an object of the class named Class in two ways −Using new keyword as −Class obj = new Class();Using the forName() method of the class named Class.Class obj = Class.forName("DemoTest");
Read MoreHow to install JDK in Windows and set up the environment variables?
Download the latest version of Java from the official site. Run the .exe to install Java on your machine. Once you installed Java on your machine, you will need to set environment variables to point to correct installation directories −Setting Up the Path for Windows:Assuming you have installed Java in c:\Program Files\java\jdk directory − Right-click on 'My Computer' and select 'Properties'.Click the 'Environment variables' button under the 'Advanced' tab.Now, alter the 'Path' variable so that it also contains the path to the Java executable. Example, if the path is currently set to 'C:\WINDOWS\SYSTEM32', then change your path to read 'C:\WINDOWS\SYSTEM32;c:\Program Files\java\jdk\bin'.
Read MoreHow to create a class and object in JShell in Java 9?
JShell is a new java shell tool released in java 9. It is the first official REPL (Read-Evaluate-Print-Loop) application. This tool helps in executing and evaluating simple java programs and logics such as statements, loops, expressions, and etc. Java REPL provides a simple programming environment in the command prompt. It can read the input, evaluate it and print the output.In the below example we can able to create a class and object in JShell using command prompt.Examplejshell> class Employee { ...> private String name; ...> Employee(String name) { ...> this.name=name; ...> ...
Read MoreHow to deserialize a JSON string using @JsonCreator annotation in Java?
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 = ...
Read MoreHow to define alternate names to a field using Jackson in Java?
The @JsonAlias annotation can define one or more alternate names for the attributes accepted during the deserialization, setting the JSON data to a Java object. But when serializing, i.e. getting JSON from a Java object, only the actual logical property name is used instead of the alias.Syntax@Target(value={ANNOTATION_TYPE, FIELD, METHOD, PARAMETER}) @Retention(value=RUNTIME) public @interface JsonAliasExampleimport com.fasterxml.jackson.annotation.*; import com.fasterxml.jackson.core.*; import com.fasterxml.jackson.databind.*; import java.io.*; public class ObjectToJsonTest { public static void main(String[] args) throws JsonProcessingException { ObjectMapper mapper = new ObjectMapper(); Technology tech = new Technology("Java", "Oracle"); ...
Read MoreJShell in Java 9?
JShell is a new concept introduced in Java 9 version. It provides Java with REPL (Read-Eval-Print-Loop) ability. By using JShell, we can test the java-based logic and expressions without compiling it. REPL acts as an immediate feedback loop and has a great effect on productivity in that particular language.Step 1: Open Command Prompt and type JShell.Microsoft Windows [Version 6.3.9600] (c) 2013 Microsoft Corporation. All rights reserved. C:\Users\User>JShell | Welcome to JShell -- Version 9.0.4 | For an introduction type: /help intro jshell>Step 2: Type /help (to view JShell commands) in the JShell command window once it starts running.jshell> /help | Type ...
Read MoreHow to define the naming conventions for JSON field names in Java?
The FieldNamingPolicy can be used to define a few standard naming conventions for JSON field names and it can be used in conjunction with GsonBuilder to configure a Gson instance to properly translate Java field names into the desired JSON field names. We can use the setFieldNamingPolicy() method of GsonBuilder to configure a specific naming policy strategy to an object's field during serialization and deserialization.Gson supports various field naming requirements with following field naming policiesFieldNamingPolicy.IDENTITY: It uses the exact same naming as the Java model when it serializes an object.FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES: It modifies a Java field name from its camel-cased form to a lower case field name where ...
Read MoreWhat is the use of underscore keyword in Java 9?
In earlier versions of Java, the underscore ("_") has used as an identifier or to create a variable name. Since Java 9, the underscore character is a reserved keyword and can't be used as an identifier or variable name. If we use a single underscore character as an identifier, the program fails to compile and throws a compile-time error because now it is a keyword and can't be used as a variable name in Java 9 or later versions.Examplepublic class UnderscoreKeywordTest { public static void main(String args[]) { int _ = ...
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