When a method is invoked on a null reference, it throws NullPointerException but in case of the static method, we can make it possible using cast expression. See the example below −ExampleLive Demopublic class Tester {    public static void display(){       System.out.println("display");    }    private void print() {       System.out.println("print");    }    public static void main(String[] args) {       //Scenario 1:       //Calling a method on null reference       //causes NullPointerException       try {          Tester test = null;     ... Read More

In the case of Event-driven programming, we pass a reference to a function which will get called when an event occurs. This mechanism is termed as a callback. Java does not support function pointers. So we can not implement the same direction. But using interfaces we can achieve the same very easily.In the example below, we've made a callback when a button is clicked. See the steps −Create an interface ClickEventHandler with a single method handleClick().Create a ClickHandler class which implements this interface ClickEventHandler.Create a Button class which will call ClickHandler when it's click method is called.Test the application.ExampleLive Demo//Step ... Read More

java.util.concurrent.The callable object can return the computed result done by a thread in contrast to a runnable interface which can only run the thread. The Callable object returns a Future object which provides methods to monitor the progress of a task being executed by a thread. The future object can be used to check the status of a Callable and then retrieve the result from the Callable once the thread is done. It also provides timeout functionality.Syntax//submit the callable using ThreadExecutor //and get the result as a Future object Future result10 = executor.submit(new FactorialService(10));   //get the result using ... Read More

PointersIn C, C++ programming languages, a pointer is a variable that holds the address of another variable.example#include using namespace std;   int main() {    //int variable    int i = 8;    //pointer variable    int * pI;    //assign the address of i to its pointer    pI = &i;    //print the number    cout

In Java, a final variable can a be assigned only once. It can be assigned during declaration or at a later stage. A final variable if not assigned any value is treated as a blank final variable. Following are the rules governing initialization of a blank final variable.A blank instance level final variable cannot be left uninitialized.The blank Instance level final variable must be initialized in each constructor.The blank Instance level final variable cannot be initialized in class methods.A blank static final variable cannot be left uninitialized.The static final variable must be initialized in a static block.A static final variable cannot ... Read More

Java supports two types of right shift operators. The >> operator is a signed right shift operator and >>> is an unsigned right shift operator. The left operands value is moved right by the number of bits specified by the right operand.Signed right shift operatorThe signed right shift operator '>>' uses the sign bit to fill the trailing positions. For example, if the number is positive then 0 will be used to fill the trailing positions and if the number is negative then 1 will be used to fill the trailing positions.Assume if a = 60 and b = -60; ... Read More

automatic resource management or try-with-resources is a new exception handling mechanism that was introduced in Java 7, which automatically closes the resources used within the try-catch block.ResourceA resource is an object which is required to be closed once our program finishes. For example, a file is read, database connection and so on.UsageTo use the try-with-resources statement, you simply need to declare the required resources within the parenthesis, and the created resource will be closed automatically at the end of the block. Following is the syntax of the try-with-resources statement.Syntaxtry(FileReader fr = new FileReader("file path")) {        // use the resource ... Read More

AssociationAssociation refers to the relationship between multiple objects. It refers to how objects are related to each other and how they are using each other's functionality. Composition and aggregation are two types of association.CompositionThe composition is the strong type of association. An association is said to composition if an Object owns another object and another object cannot exist without the owner object. Consider the case of Human having a heart. Here Human object contains the heart and heart cannot exist without Human.AggregationAggregation is a weak association. An association is said to be aggregation if both Objects can exist independently. For ... Read More

It is an algorithm to perform factorization on given integers. Following is the program implementing the Rho Algorithm for Prime Factorization.ProgramLive Demopublic class PollardsRho {    int num = 65;    public int gcd(int a, int b) {       int gcd = 0;       for(int i = 1; i

Sieve of Eratosthenes is the ancient algorithm to find prime numbers up to a given number.Algorithm1. Generate integers from 2 to n (Given number).2. Counting from 2 mark every 2nd integer. (multiples of 2)3. Now, starting from 3 mark every third integer. (multiples of 3)4. Finally, marking from 5 mark every 5th integer.(multiples of 5)Programimport java.util.Scanner; public class SievePrimeFactors  {    public static void main(String args[]) {       Scanner sc = new Scanner(System.in);       System.out.println("Enter a number");       int num = sc.nextInt();       boolean[] bool = new boolean[num];       ... Read More