Often, you will want to cycle through the elements in a collection. For example, you might want to display each element. The easiest way to do this is to employ an iterator, which is an object that implements either the Iterator or the ListIterator interface.Iterator enables you to cycle through a collection, obtaining or removing elements. ListIterator extends Iterator to allow bidirectional traversal of a list, and the modification of elements.Before you can access a collection through an iterator, you must obtain one. Each of the collection classes provides an iterator( ) method that returns an iterator to the start ... Read More

isInstance method is equivalent to instanceof operator. The method is used in case of objects are created at runtime using reflection. General practice says if type is to be checked at runtime then use isInstance method otherwise instanceof operator can be used. See the example below −Example Live Demopublic class Tester{    public static void main(String[] args) throws ClassNotFoundException {       Integer i = new Integer(10);       System.out.println(usingInstanceOf(i));       System.out.println(usingIsInstance(i));    }    public static String usingInstanceOf(Object i){       if(i instanceof String){          return "String";       } ... Read More

final is a non-access modifier for Java elements. The final modifier is used for finalizing the implementations of classes, methods, and variables. A final instance variable can be explicitly initialized only once.A final instance variable should be initialized at one of the following occasions −At time of declaration.In constructor.In instance block.Compiler will throw error, it a final variable is not initialized at all using any of the above methods. Following examples showcases example of instance variables as final.Example Live Demopublic class Tester{    final int A = 1;    final int B;{       B = 2;    }   ... Read More

A set is a collection which does not allows duplicate values. HashSet is an implementation of a Set. Following are the ways in which we can initialize a HashSet in Java.Using constructor − Pass a collection to Constructor to initialize an HashSet.Using addAll() − Pass a collection to Collections.addAll() to initialize an HashSet.Using unmodifiableSet() − Pass a collection to Collections.unmodifiableSet() to get a unmodifiable Set.Using add() − Using add(element) method of Set.Following is an example of using above ways.ExampleInfinityNow consider the following code snippet.Example Live Demoimport java.util.Arrays; import java.util.Collections; import java.util.HashSet; import java.util.List; import java.util.Set; public class Tester{    public ... Read More

Consider the following code snippet where we divide a number by 0.Example Live Demopublic class Tester{    public static void main(String[] args) {       double d = 100;       System.out.println(d/0);    } }OutputInfinityNow consider the following code snippet.Example Live Demopublic class Tester{    public static void main(String[] args) {       int d = 100;       System.out.println(d/0);    } }OutputException in thread "main" java.lang.ArithmeticException: / by zero at Tester.main(Tester.java:5)As you've noted, the Infinity vs ArithmeticException, a different result for similar divide by zero program. The difference lies in floating point arithmetic used in first program and integer arithmetic used in second program.

We can create Thread by either by implementing a runnable interface or by extending Thread class. Below are the detailed steps of using both ways to create Thread.Create a Thread by Implementing a Runnable InterfaceIf your class is intended to be executed as a thread then you can achieve this by implementing a Runnable interface. You will need to follow three basic steps −Step 1As a first step, you need to implement a run() method provided by a Runnable interface. This method provides an entry point for the thread and you will put your complete business logic inside this method. ... Read More

Java uses call by value while passing parameters to a function. To swap objects, we need to use their wrappers. See the example below −Example Live Demopublic class Tester{    public static void main(String[] args) {       A a = new A();       A b = new A();       a.value = 1;       b.value = 2;       //swap using objects       swap(a, b);       System.out.println(a.value +", " + b.value);       Wrapper wA = new Wrapper(a);       Wrapper wB = new ... Read More

A Singleton pattern states that a class can have a single instance and multiple instances are not permitted to be created. For this purpose, we make the constructor of the class a private and return a instance via a static method. But using serialization, we can still create multiple instance of a class. See the example below −Example - Breaking Singleton Live Demoimport java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.Serializable; public class Tester{    public static void main(String[] args)    throws ClassNotFoundException, IOException{       A a = A.getInstance();       A b ... Read More

A Singleton pattern states that a class can have a single instance and multiple instances are not permitted to be created. For this purpose, we make the constructor of the class a private and return a instance via a static method. But using reflection, we can still create multiple instance of a class by modifying the constructor scope. See the example below −Example - Breaking Singleton Live Demoimport java.io.Serializable; import java.lang.reflect.Constructor; import java.lang.reflect.InvocationTargetException; public class Tester {    public static void main(String[] args) throws    InstantiationException, IllegalAccessException,    IllegalArgumentException, InvocationTargetException{       A a = A.getInstance();     ... Read More

A Singleton pattern states that a class can have a single instance and multiple instances are not permitted to be created. For this purpose, we make the constructor of the class a private and return a instance via a static method. But using cloning, we can still create multiple instance of a class. See the example below −Example - Breaking Singletonpublic class Tester{    public static void main(String[] args)    throws CloneNotSupportedException {       A a = A.getInstance();       A b = (A)a.clone();       System.out.println(a.hashCode());       System.out.println(b.hashCode());    } } ... Read More