Article Categories
- All Categories
-
Data Structure
-
Networking
-
RDBMS
-
Operating System
-
Java
-
MS Excel
-
iOS
-
HTML
-
CSS
-
Android
-
Python
-
C Programming
-
C++
-
C#
-
MongoDB
-
MySQL
-
Javascript
-
PHP
-
Economics & Finance
Object Oriented Programming Articles
Page 219 of 589
Is parent child hierarchy important on throws while overriding in Java?
When you try to handle an exception (checked) thrown by a particular method, you need to catch it using the Exception class or super class of the Exception occurred.In the same way while overriding the method of a super class, if it throws an exception −The method in the sub-class should throw the same exception or its sub type.The method in the sub-class should not throw its super type.You can override it without throwing any exception.When you have three classes named Demo, SuperTest and, Super in (hierarchical) inheritance, if Demo and SuperTest have a method named sample().Exampleclass Demo { ...
Read MoreWhat is meant by re-throwing exceptions in Java?
When an exception is cached in a catch block, you can re-throw it using the throw keyword (which is used to throw the exception objects).While re-throwing exceptions you can throw the same exception as it is without adjusting it as −try { int result = (arr[a])/(arr[b]); System.out.println("Result of "+arr[a]+"/"+arr[b]+": "+result); } catch(ArithmeticException e) { throw e; }Or, wrap it within a new exception and throw it. When you wrap a cached exception within another exception and throw it, it is known as exception chaining or, exception wrapping, by doing this you can adjust your exception, throwing a ...
Read MoreHow to avoid ConcurrentModificationException while iterating a collection in java?
When you are working with collection objects, while one thread is iterating over a particular collection object, if you try to add or remove elements from it, a ConcurrentModificationException will be thrown.Not only that, If you are iterating a collection object, add or remove elements to it and try to iterate its contents again it is considered that you are trying to access the collection object using multiple threads and ConcurrentModificationException is thrown.Exampleimport java.util.ArrayList; import java.util.Iterator; public class OccurenceOfElements { public static void main(String args[]) { ArrayList list = new ArrayList(); //Instantiating ...
Read MoreWhat is the difference between getter/setter methods and constructor in Java?
ConstructorsA constructor in Java is similar to method and it is invoked at the time creating an object of the class, it is generally used to initialize the instance variables of a class. The constructors have the same name as their class and, have no return type.If you do not provide a constructor the compiler defines one on your behalf, which initializes the instance variables with default values.You can also accept parameters through constructors and initialize the instance variables of a class using the given values, these are known as parameterized constructors.ExampleThe following Java program has a class named student ...
Read MoreCan we initialize static variables in a default constructor in Java?
Class/static variables belong to a class, just like instance variables they are declared within a class, outside any method, but, with the static keyword.They are available to access at the compile time, you can access them before/without instantiating the class, there is only one copy of the static field available throughout the class i.e. the value of the static field will be same in all objects. You can define a static field using the static keyword.If you declare a static variable in a class, if you haven’t initialized it, just like with instance variables compiler initializes these with default values ...
Read MoreWhat is deep copy? Explain with an example in Java.
Creating an exact copy of an existing object in the memory is known as cloning.The clone() method of the class java.lang.Object accepts an object as a parameter, creates and returns a copy of it (clones).In order to use this method, you need to make sure that your class implements the Cloneable interface.Exampleimport java.util.Scanner; public class CloneExample implements Cloneable { private String name; private int age; public CloneExample(String name, int age){ this.name = name; this.age = age; } public void displayData(){ System.out.println("Name : "+this.name); ...
Read MoreCopy all elements of ArrayList to an Object Array in Java
All the elements of an ArrayList can be copied into an Object Array using the method java.util.ArrayList.toArray(). This method does not have any parameters and it returns an Object Array that contains all the elements of the ArrayList copied in the correct order.A program that demonstrates this is given as follows −Exampleimport java.util.ArrayList; import java.util.List; public class Demo { public static void main(String[] args) { List aList = new ArrayList(); aList.add("Nathan"); aList.add("John"); aList.add("Susan"); aList.add("Betty"); aList.add("Peter"); Object[] objArr = ...
Read MoreIterate over the elements of HashSet in Java
Declare a HashSet and add elements −Set hs = new HashSet(); hs.add(20); hs.add(39); hs.add(67); hs.add(79);Now, iterate over the elements −for (Iterator i = hs.iterator(); i.hasNext();) { Object ele = i.next(); System.out.println(ele); }The following is an example that iterate over the elements of HashSet −Exampleimport java.util.HashSet; import java.util.Iterator; import java.util.Set; public class Demo { public static void main(String[] argv) throws Exception { Set hs = new HashSet(); hs.add(20); hs.add(39); hs.add(67); hs.add(79); System.out.println("Elements = "); for (Iterator i ...
Read MoreConvert array to HashSet in Java
Create an array and convert it to List −Integer[] arr = { 10, 15, 20, 10, 10, 10, 20, 30, 35, 40, 40}; List l = Arrays.asList(arr);Now, let us convert the above array to HashSet −Set s = new HashSet(l);The following is an example to convert array to HashSet −Exampleimport java.util.*; public class Demo { public static void main(String[] argv) throws Exception { Integer[] arr = { 10, 15, 20, 10, 10, 10, 20, 30, 35, 40, 40}; List l = Arrays.asList(arr); Set s = new HashSet(l); for (Iterator i = s.iterator(); i.hasNext();) { Object ele = i.next(); System.out.println(ele); } } }Output35 20 40 10 30 15
Read MoreNavigableMap clear() Method in Java
Clear the NavigableMap in Java, using the clear() method.Let us first create a NavigableMap and add some elements to it −NavigableMap n = new TreeMap(); n.put(5, "Tom"); n.put(9, "John"); n.put(14, "Jamie"); n.put(1, "Tim"); n.put(4, "Jackie"); n.put(15, "Kurt"); n.put(19, "Tiger"); n.put(24, "Jacob");Now, use the clear() method −n.clear();The following is an example to implement clear() method and clear the NavigableMap −Exampleimport java.util.*; public class Demo { public static void main(String[] args) { NavigableMap n = new TreeMap(); n.put(5, "Tom"); n.put(9, "John"); n.put(14, "Jamie"); n.put(1, "Tim"); ...
Read More