Java Articles - Page 158 of 440

ArrayList to ArrayList Instead of the typed parameter in generics (T) you can also use “?”, representing an unknown type. These are known as wild cards you can use a wild card as − Type of parameter or, a Field or, a Local field. Using wild cards, you can convert ArrayList to ArrayList as − ArrayList stringList = (ArrayList)(ArrayList)(list); Example import java.util.ArrayList; import java.util.Iterator; import java.util.ListIterator; public class ArrayListExample { public static void main(String args[]) { //Instantiating an ArrayList object ... Read More

Jackson is a Java-based library, and it can be useful for converting Java objects to JSON and JSON to Java objects. A Jackson API is faster than other API, needs less memory, and is good for large objects. We can convert a JSON array to a list using the ObjectMapper class. It has a useful method,  readValue(), which takes a JSON string and converts it to the object class specified in the second argument. Before proceeding further, first of all, we need to import the Jackson library into our project. To do this, you can add the following dependency to ... Read More

The Flexjson is a lightweight library for serializing and deserializing Java objects into and from JSON format. We can serialize a list of objects using the serialize() method of JSONSerializer class. This method can perform a shallow serialization of the target instance. We need to pass a list of objects of List type as an argument to the serialize() method.Syntaxpublic String serialize(Object target)Exampleimport flexjson.JSONSerializer; import java.util.*; public class JsonSerializeListTest {    public static void main(String[] args) {       JSONSerializer serializer = new JSONSerializer().prettyPrint(true); // pretty print JSON       Student s1 = new Student("Raja", "Ramesh", 28, "Hyderabad");       Student s2 = new Student("Suresh", "Kumar", 30, "Chennai");   ... Read More

JSON is a format for storing and exchanging data. It is easily readable and also easy to parse. Creating JSON Using Java JsonGenerator In Java, we can create a JSON object using the JsonGenerator class. JsonGenerator is class in the javax.json.stream package that is used to create JSON data. It provides methods to write JSON objects, arrays, and values. To use the JsonGenerator class, we need to add the javax.json library to our project. If you are using Maven, add this to your pom.xml file: javax.json javax.json-api 1.1.4 If you are not using Maven, you can download ... Read More

How to create a variable that can be set only once, meaning it can be assigned a value only once but is not final in Java? Solution In Java we can solve the above using the following two methods: Using a custom wrapper class Using an AtomicReference Using a custom wrapper class We can create a custom wrapper class that allows setting a value only once. The class will have a boolean flag to check if the value has already been set. Wrapper classes are used for converting primitive data types into objects. We will use this for setting ... Read More

Problem Statement The task is, given a string and a substring, you have to check if a substring is present in a string or not. Do not mind if the case of the string and substring is different, it should not matter. For example, if the string is "Hello World" and the substring is "hello", then the output should be true. Even if the substring is "HELLO" or "HeLLo", the output should be true. Solution To solve this problem, we will first convert the string and the substring to lowercase using the toLowerCase() method. The toLowerCase () method of the ... Read More

ArrayList is a part of the Java Collections Framework. Which is a dynamic type of array that can grow and shrink as needed. It is a resizable array implementation of the List interface. The ArrayList class is used when we want to store a list of elements in a dynamic array. In this article, let's learn how to get the first and last elements from an ArrayList in Java. The get() method of the ArrayList class accepts an integer representing the index value and returns the element of the current ArrayList object at the specified index. Therefore, if you pass ... Read More

Using copyOf() methodThe copyOf() method of the Arrays class (java.util package) accepts two parameters −an array (of any type).an integer value representing length.And copies the contents of the given array from starting position to given length and returns the new array.Example Live Demoimport java.util.Arrays; public class CopyingSectionOfArray {    public static void main(String[] args) {       String str[] = new String[10];       //Populating the array       str[0] = "Java";       str[1] = "WebGL";       str[2] = "OpenCV";       str[3] = "OpenNLP";       str[4] = "JOGL";     ... Read More

Problem Statement The given problem is to validate a string to check if that string contains only alphabets (both uppercase and lowercase) and does not contains any other characters like numbers, special characters, etc.. For example, the string "HelloWorld" is valid as it contains only alphabets, while "Hello123" is not valid as it contains numbers. Solution We can solve this problem by using following methods: Using Regular Expressions Manual Checking using loop Using Character.isAlphabetic() Using Regular Expressions We can use regular expressions to validate a string for alphabets. The regular expression ^[a-zA-Z]+$ matches a string that contains only ... Read More

Problem Statement Here we have a string that contains integer values, our task is to sort those integer values in ascending order. For example, if the string is "31134", the sorted string should be "11334". Solution We can solve the above problem using multiple ways: Using char array Using Stream API Using Bubble Sort Using char array We will use the toCharArray() method of the String class to convert the string into a character array. Then we will sort the character array using the Arrays.sort() method. ... Read More