Write a program to Check if a number is even or odd is one of basic question which will be asked in the interview for fresher, anyone can solve this but always this question comes with a twist given at the end stating that we should not use the modulo or division operator in Java. Before getting into the actual code to begin with lets use the modulo and division operation to … [Read more...]
Top 17 Core Java Interview Questions on Constructors
1. What is a Constructor in Java? Constructor is just like a method in Java that is used to initialize the state of an object and will be invoked during the time of object creation. 2. What are the Rules for defining a constructor? Constructor name should be the same as the class name It cannot contain any return type It can have all Access Modifiers are allowed … [Read more...]
Top 14 Java Interview Questions on Static keyword
1. What is static keyword in Java? Static is a Non-Access Modifier. Static can be applied to variable, method, nested class and initialization blocks (static block). 2. What is a static variable? A Static variable gets memory allocated only once during the time of class loading. All the instance of the class share the same copy of the variable, a static variable can … [Read more...]
Polymorphism in Java – Method Overloading and Overriding
Polymorphism is the ability to take more than one form. Polymorphism is one of the most important concept in OOPS ( Object Oriented Programming Concepts). Subclasses of a class can define their own unique behaviors and yet share some of the same functionality of the parent class. In Java, there are 2 ways by which you can achieve polymorphic behavior 1. Method … [Read more...]
How to Create an Immutable Class in Java
Immutable class is the one whose state cannot be changed after it is created. The best example for this is String,Integer class in Java, once instantiated the value never be changed. In this article, lets learn How to Create an Immutable Class in Java. Immutable class has lots of advantages such as they can be used for the caching purposes as you don't need to worry about … [Read more...]
How HashMap works in Java
How a HashMap Works internally has become a popular question in almost all the interview. As almost everybody knows how to use a HashMap or the difference between HashMap and Hashtable. But many fails when the question is how does a hashmap internally works. So the answer to the question how does a hashmap works is that is it works based on the hashing principle but it is … [Read more...]
Difference between HashMap and Hashtable | HashMap Vs Hashtable
Both the HashMap and Hashtable implement the interface java.util.Map but there are some slight differences which has to be known to write a much efficient code. The Most important difference between HashMap and the Hashtable is that Hashtable is synchronized and HashMap is non-synchronized , which means Hashtable is thread-safe and can be shared among multiple threads and … [Read more...]
Difference between Enumeration and Iterator ?
Both Enumeration and Iterator is used for traversing through the underlying Collection. Enumeration can traverse limited collection such as Vectors and HashTable. Whereas Iterator can be used to almost all the Collection. Enumeration is twice as fast as Iterator as it act as read-only interface on the other hand Iterator is much safer as it doesn't allow any modification to the … [Read more...]
Difference between fail-fast and fail-safe Iterator
Difference between fail-fast and fail-safe Iterator has become one of the favorite question for many interviewers as it has a slight flavors of concurrency. Java provides the iterator to iterate the objects in the Collection. The rule is that the Collection should not be altered when iterating, if modified you will get the ConcurrentModificationException. Fail-Fast … [Read more...]
Difference Between Interface and Abstract Class in Java
This is one of the most frequently asked questions in the interview. Many interviewers will not leave this topic. So let's see the difference between them The main difference is that the Interfaces are implicitly abstract and cannot have implementation, whereas an abstract class can have a concrete class. Interface is implemented using the "implements" keyword. Abstract … [Read more...]
Difference between equals() and ==
Both equals() and '==' is used to check the equality of the objects but there is a significant amount of difference between equals() and '=='. The equals method is present in the java.lang.Object class and it is used to check the equivalence of the object (i.,e) to check if the content is equal whereas '==' is used to check if the actual object instances are same or not. … [Read more...]
Sort Objects in a ArrayList using Java Comparable Interface
In my previous post you would have learnt how to sort objects in a ArrayList using java comparator. Using the Comparable interface is almost the same as the previous, but here instead of a separate class for implementing the Comparator interface we can implement it in the same Employee Class by overriding the compareTo() method instead of the compare() method. Let see how the … [Read more...]