The volatile modifier is used to let the JVM know that a thread accessing the variable must always merge its own private copy of the variable with the master copy in the memory.Accessing a volatile variable synchronizes all the cached copied of the variables in the main memory. Volatile can only be applied to instance variables, which are of type object or private. A volatile object reference can be null.Examplepublic class MyRunnable implements Runnable {    private volatile boolean active;    public void run() {       active = true;       while (active) {       }    }    public void stop() {       active = false;    } }

When we start two or more threads within a program, there may be a situation when multiple threads try to access the same resource and finally they can produce unforeseen result due to concurrency issues. For example, if multiple threads try to write within a same file then they may corrupt the data because one of the threads can override data or while one thread is opening the same file at the same time another thread might be closing the same file.So there is a need to synchronize the action of multiple threads and make sure that only one thread ... Read More

A string is Palindrome if position of each character remain same in case even string is reversed.For example 'MADAM' is a palidrome string as position of each character remain same even if string 'MADAM' is reversed.Now in order to identify a string as palindrome or not we can use library method approach and also without library method approach.But if we want to check if "Madam" is palindrome or not , it will show us that it is not a palindrome because of the upper case of first letter.Example - Without library method. Live Demopublic class Palindrome {    public static void ... Read More

To count occurrences of vowels in a string again use the Map utility of Java as used in calculating the occurrence of each character in the string. Put each vowel as a key in Map and put the initial value as 1 for each key. Now compare each character with the key of the map if a character matches with a key then increase its corresponding value by 1. Steps to check occurrence of each vowel in String Following are the steps to check occurrence of each vowel in String − First, we will define ... Read More

The java.util.LinkedList.listIterator(int index) method returns a list-iterator of the elements in this list (in proper sequence), starting at the specified position in the list.DeclarationFollowing is the declaration for java.util.LinkedList.listIterator() methodpublic ListIterator listIterator(int index)Parametersindex − index of the first element to be returned from the list-iteratorReturn ValueThis method returns a ListIterator of the elements in this list (in proper sequence), starting at the specified position in the listExceptionIndexOutOfBoundsException − if the index is out of rangeExampleThe following example shows the usage of java.util.LinkedList.listIterator() method.Example Live Demopackage com.tutorialspoint; import java.util.*; public class LinkedListDemo {    public static void main(String[] args) { ... Read More

Optional is a container object used to contain not-null objects. Optional object is used to represent null with absent value. This class has various utility methods to facilitate code to handle values as 'available' or 'not available' instead of checking null values. It is introduced in Java 8 and is similar to what Optional is in Guava.Class DeclarationFollowing is the declaration for java.util.Optional class −public final class Optional extends ObjectClass MethodSr.No.Method & Description1static Optional empty()Returns an empty Optional instance.2boolean equals(Object obj)Indicates whether some other object is "equal to" this Optional.3Optional filter(PredicateRead More

instanceof operator is used to check the type of object passed. Following rules explain the usage of instanceof operator in Java.instanceof operator returns true for the object if checked against its class type.instanceof operator returns false for the object if checked against its type which is not in its hierarchy.instanceof operator returns true for the child object if checked against parent object type.instanceof operator returns true for the complete object hierarchy up to the Object class.instanceof operator returns false for the null value.instanceof operator returns false for the parent object if checked against child object type.Following example showcases the above ... Read More

In Java, we use inheritance to allow the creation of a hierarchical classification of classes and objects. As the name suggests, inheritance is the ability of a class to inherit members of another class. The class whose properties are inherited is called a superclass whereas the class that inherits a superclass is called a subclass. We use the extends keyword to inherit the class. There are several types of inheritance in Java such as single and multilevel. In this article, we will specifically explore the multiple inheritance. Multiple Inheritance in Java In the terminology of object-oriented programming, multiple inheritance is ... Read More

Jagged array is a multidimensional array where member arrays are of different size. For example, we can create a 2D array where first array is of 3 elements, and is of 4 elements. Following is the example demonstrating the concept of jagged array.Example Live Demopublic class Tester {    public static void main(String[] args){       int[][] twoDimenArray = new int[2][];       //first row has 3 columns       twoDimenArray[0] = new int[3];       //second row has 4 columns       twoDimenArray[1] = new int[4];       int counter = ... Read More

Collections can be iterated easily using two approaches.Using for-Each loop − Use a foreach loop and access the array using object.Using Iterator − Use a foreach loop and access the array using object.DifferencesConcurrentModificationException − Using for-Each loop, if an object is modified, then ConcurrentModificationException can occur. Using iterator, this problem is elliminated.Size Check − Using for-Each, size check is not required. Using iterator if hasNext() is not used properly, NoSuchElementException can occur.Performance − Performance is similar for both cases.Following is an example of using above ways.Example Live Demoimport java.util.ArrayList; import java.util.Iterator; import java.util.List; public class Tester {    public ... Read More