Found 346 Articles for Java Programming

Externalization is used whenever we need to customize serialization mechanism. If a class implements an Externalizable interface then, object serialization will be done using writeExternal() method. Whereas at receiver's end when an Externalizable object is a reconstructed instance will be created using no argument constructor and then the readExternal() method is called.If a class implements only Serializable interface object serialization will be done using ObjectoutputStream. At the receiver's end, the serializable object is reconstructed using ObjectInputStream.Below example showcases usage of Externalizable interface.Exampleimport java.io.Externalizable; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.ObjectInput; import java.io.ObjectInputStream; import java.io.ObjectOutput; import java.io.ObjectOutputStream; public class ... Read More

Runtime Polymorphism in Java is achieved by Method overriding in which a child class overrides a method in its parent. An overridden method is essentially hidden in the parent class, and is not invoked unless the child class uses the super keyword within the overriding method. This method call resolution happens at runtime and is termed as Dynamic method dispatch mechanism.ExampleLet us look at an example.class Animal {    public void move() {       System.out.println("Animals can move");    } } class Dog extends Animal {    public void move() {       System.out.println("Dogs can walk and ... Read More

We can download a web page using its URL in Java. Following are the steps needed.Create URL object using url string.Download webpage in JavaCreate a BufferReader object using url.openStream() method.BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream()));Create a BufferWriter object to write to a file.BufferedWriter writer = new BufferedWriter(new FileWriter("page.html"));Read each line using BufferReader and write using BufferWriter.String line; while ((line = reader.readLine()) != null) { writer.write(line); }Following is the complete program to download a given URL page at current location.import java.io.BufferedReader; import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; import java.io.InputStreamReader; import java.net.URL; public class Tester {    public static void main(String ... Read More

Double braces can be used to create and initialize objects in a single Java expression. See the example below −Exampleimport java.util.ArrayList; import java.util.List; public class Tester{    public static void main(String args[]) {       List list = new ArrayList();       list.add("A");       list.add("B");       list.add("C");       list.add("D");       list.add("E");       list.add("F");       System.out.println(list);       List list1 = new ArrayList() {       {          add("A"); add("B");add("C");          add("D");add("E");add("F");       ... Read More

Forward declarations means the declaration of a method or variable prior to its implementation. Such declaration is necessary in C/C++ programming language in order to be able to use a variable or object before its implementation. In case, if we want to use a library code, then we need to create its header file and use it. But this is not a case in Java.Java allows using a variable, class prior to its declaration and implementation.Java allows using libraries code without any need of header files.Following example showcases the same. Here we have used a class object before its declaration.Examplepublic ... Read More

Following are the different ways to handle exception messages in Java.Using printStackTrace() method − It print the name of the exception, description and complete stack trace including the line where exception occurred.catch(Exception e) { e.printStackTrace(); }Using toString() method − It prints the name and description of the exception.catch(Exception e) { System.out.println(e.toString()); }Using getMessage() method − Mostly used. It prints the description of the exception.catch(Exception e) { System.out.println(e.getMessage()); }Exampleimport java.io.Serializable; public class Tester implements Serializable, Cloneable {    public static void main(String args[]) {       try {          int a = 0;     ... Read More

Following are the different ways to convert an Integer to String in Java.Using Integer.toString(int) − Convert an int to String using static toString() method of Integer class.String b = Integer.toString(125);Using String.valueOf(int) − Convert an int to String using static valueOf() method of String class.String b = String.valueOf(125);Using new Integer(int).toString() − Convert an int to String using toString() method of Integer object.String b = new Integer(125).toString();Using DecimalFormat(pattern).format(int) − Convert an int to String using DecimalFormat.format() method.String b = new DecimalFormat("#").format(125);Using StringBuilder().toString() − Convert an int to String using StringBuilder.toString() method.String b = new StringBuilder().append(125).toString();Using StringBuffer().toString() − Convert an int to String ... Read More

Following are the notable differences between super() and this() methods in Java. super()this()Definitionsuper() - refers immediate parent class instance.this() - refers current class instance.InvokeCan be used to invoke immediate parent class method.Can be used to invoke current class method.Constructorsuper() acts as immediate parent class constructor and should be first line in child class constructor.this() acts as current class constructor and can be used in parametrized constructors.OverrideWhen invoking a superclass version of an overridden method the super keyword is used.When invoking a current version of an overridden method the this keyword is used.Example Live Democlass Animal {    String name;    Animal(String name) ... Read More

HashMap, TreeMap and LinkedHashMap all implements java.util.Map interface and following are their characteristics.HashMapHashMap has complexity of O(1) for insertion and lookup.HashMap allows one null key and multiple null values.HashMap does not maintain any order.TreeMapTreeMap has complexity of O(logN) for insertion and lookup.TreeMap does not allow null key but allow multiple null values.TreeMap maintains order. It stores keys in sorted and ascending order.LinkedHashMapLinkedHashMap has complexity of O(1) for insertion and lookup.LinkedHashMap allows one null key and multiple null values.LinkedHashMap maintains order in which key-value pairs are inserted.Exampleimport java.util.HashMap; import java.util.Hashtable; import java.util.LinkedHashMap; import java.util.Map; import java.util.TreeMap; public class Tester { ... Read More

Following are the notable differences between HashTable and HashMap classes in Java. HashTableHashMapSynchronizedHashTable is synchronized.HashMap is not synchronized.Thread SafeHashTable is thread safe.HashMap is not thread safe.Null objectsHashTable does not allows null keys or null values.HashMap allows one null key and multiple null values.PerformanceHashTable is faster.HashMap is slower than HashTable.Since Java Version1.21.5Exampleimport java.util.HashMap; import java.util.Hashtable; import java.util.Map; public class Tester {    public static void main(String args[]) {       Map map = new HashMap();       map.put("1", "One");       map.put("2", "Two");       map.put("3", "Three");       map.put("5", "Five");       ... Read More