More than 3000 questions in repository. There are more than 900 unanswered questions. Click here and help us by providing the answer. Have a video suggestion. Click Correct / Improve and please let us know.
Ans. Builder is a creational Design Pattern whereas Composite is a structural design pattern. Composite creates Parent - Child relations between your objects while Builder is used to create group of objects of predefined types.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Factory is a creational design pattern whereas Strategy is behavioral design pattern. Factory revolves around the creation of object at runtime whereas Strategy or Policy revolves around the decision at runtime.
Help us improve. Please let us know the company, where you were asked this question :
Ans. As we only downcast class in the hierarchy, The ClassCastException is thrown to indicate that code has attempted to cast an object to a subclass of which it is not an instance.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Garbage Collector wont remove a strong reference.
A soft reference will only get removed if memory is low.
A weak reference will get removed on the next garbage collection cycle.
A phantom reference will be finalized but the memory will not be reclaimed. Can be useful when you want to be notified that an object is about to be collected.
Help us improve. Please let us know the company, where you were asked this question :
Ans. instance variables and objects are stored on heap and the references are stored on stack whereas static variables are stored in the method area of heap.
Help us improve. Please let us know the company, where you were asked this question :
Ans. 1.this is a reference to the current object in which this keyword is used whereas super is a reference used to access members specific to the parent Class.
2.this is primarily used for accessing member variables if local variables have same name, for constructor chaining and for passing itself to some method whereas super is primarily used to initialize base class members within derived class constructor.
Help us improve. Please let us know the company, where you were asked this question :
Ans. The jsp scriptlet tag can only declare variables not methods whereas jsp declaration tag can declare variables as well as methods.
The declaration of scriptlet tag is placed inside the _jspService() method whereas The declaration of jsp declaration tag is placed outside the _jspService() method.
Help us improve. Please let us know the company, where you were asked this question :
Ans. A source of possible errors in parallel programming, where one thread can cause an error in another thread by changing some aspect of the state of the program that the second thread is depending on (such as the value of variable).
Help us improve. Please let us know the company, where you were asked this question :
Ans. Collections can only hold objects, It can't hold primitive data types.
Collections have performance overheads as they deal with objects and offer dynamic memory expansion. This dynamic expansion could be a bigger overhead if the collection class needs consecutive memory location like Vectors.
Collections doesn't allow modification while traversal as it may lead to concurrentModificationException.
Help us improve. Please let us know the company, where you were asked this question :
LikeDiscussCorrect / Improve java collections collections classes disadvantages of collections over arrays collections vs arrays
Q183. What is Generalization and Specialization in terms of casting ?
Ans. Generalization or UpCasting is a phenomenon where a sub class is prompted to a super class, and hence becomes more general. Generalization needs widening or up-casting. Specialization or DownCasting is a phenomenon where a super class is narrowed down to a sub class. Specialization needs narrowing or down-casting.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Yes, We can call garbage collector directly but it doesn't guarantees that the gc will start executing immediately. This gc( ) method appears in both Runtime and System classes of java.lang package.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Both belong to the class as a whole and not to the individual objects. Static methods are explicitly called for execution whereas Static block gets executed when the Class gets loaded by the JVM.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Java uses Just-In-Time compiler to enable high performance. Just-In-Time compiler is a program that turns Java bytecode into instructions that can be sent directly to the processor.
Help us improve. Please let us know the company, where you were asked this question :
Ans. A child object constructor always first needs to construct its parent. In Java it is done via an implicit call to the no-args constructor as the first statement
Help us improve. Please let us know the company, where you were asked this question :
Ans. At the beginning of an object's life, the Java virtual machine (JVM) allocates memory on the heap to accommodate the object's instance variables. When that memory is first allocated, however, the data it contains is unpredictable. If the memory were used as is, the behavior of the object would also be unpredictable. To guard against such a scenario, Java makes certain that memory is initialized, at least to predictable default values before it is used by any code.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Iterators in java are used to iterate over the Collection objects.
Fail-Fast iterators immediately throw ConcurrentModificationException if there is any addition, removal or updation of any element.
Fail-Safe iterators don't throw any exception if a collection is structurally modified while iterating over it. This is because, they operate on the clone of the collection and not on the original collection.
Help us improve. Please let us know the company, where you were asked this question :
Ans. The Spring Application starts with the main() method. Spring Application has a Main Class where main() method has a static method run() which takes two arguments, one is class type and second is string array.
Spring Application will bootstrap our application, starts auto-configured tomcat web server.When SpringApplication.run() command is invoked, the Application Context is created. The createApplicationContext method checks if it is a web or standalone application based on the type it creates for the context.When the constructor of the context is invoked, it will register the annotated class beans with the context. All your @Repository, @Component, @Service, and Controller beans will be registered and the context is returned.
Help us improve. Please let us know the company, where you were asked this question :
Q191. Will the static block be executed in the following code ? Why ?
class Test { static { System.out.println("Why I am not executing "); } public static final int param=20; }
public class Demo { public static void main(String[] args) { System.out.println(Test.param); } }
Ans. No the static block won't get executed as the referenced variable in the Test class is final. Compiler replaces the content of the final variable within Demo.main method and hence actually no reference to Test class is made.
Help us improve. Please let us know the company, where you were asked this question :
Ans. The purpose of comparator interface is to compare objects of the same class to identify the sorting order. Sorted Collection Classes ( TreeSet, TreeMap ) have been designed such to look for this method to identify the sorting order, that is why class need to implement Comparator interface to qualify its objects to be part of Sorted Collections.
Help us improve. Please let us know the company, where you were asked this question :
Ans. 1. Methods can participate in runtime polymorphism whereas member variables cannot.
For example -
Vehicle vehicle = new Car();
car.getObjVariable();// will return variable defined in Car
whereas
car.variable
will return the variable from Car class irrespective of the object it holds.
2. Validations can be performed before setting the variables.
3. If the input format changes or some other value or calculated value needs to be returned , that can be absorbed by making change ( wrapping ) in the setter and getter. By this the call to method from outside or interface to the object will remain the same.
Help us improve. Please let us know the company, where you were asked this question :
Ans. Yes, but the overloaded main methods without single String[] argument doesn't get any special status by the JVM. They are just another methods that needs to be called explicitly.
Help us improve. Please let us know the company, where you were asked this question :
Ans. 1. Configure Provider class in Hibernate configuration file.
2. Add Cache usage tag ( read-only or read-write ) in mapping files ( hbm ).
3. Create an XML file called ehcache.xml and place in classpath which contains time settings and update settings, behavior of cache , lifetime and idletime of Pojos, how many objects are allowed.
Help us improve. Please let us know the company, where you were asked this question :
Ans. No. compareTo method is declared final for the Enumerations and hence cannot be overriden. This has been intentionally done so that one cannot temper with the sorting order on the Enumeration which is the order in which Enum constants are declared.
Help us improve. Please let us know the company, where you were asked this question :
Q199. If you are given a choice to implement the code to either Insert a Record or Update if already exist, Which approach will you follow ?
1. Insert into the DB Table. If exception occurs, update the existing record. 2. Check if the record exists and update it if it exists, If not insert a new record.
Ans. throw is used to re throw an exception.throws is used to declare that the method throws the respective exceptions.try block is used to identify if the respective block has thrown any exception.catch is used to catch the exception that has been thrown by the respective try block.
Help us improve. Please let us know the company, where you were asked this question :
More than 3000 questions in repository.
Discuss 
java design pattern builder composite creational design pattern structural design pattern
Asked in 1 Companies 
expert
Sample Code for reflection
frequent
Try 2 Question(s) Test
Very Frequently asked.
Which of the following can throw ClassCastException ?
