Core Java - Interview Questions and Answers for 'Frequent' | Search Interview Question

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Q151. Why java doesn't support multiple Inheritence ?

Ans. class A {
void test() {
System.out.println("test() method");
}
}

class B {
void test() {
System.out.println("test() method");
}
}

Suppose if Java allows multiple inheritance like this,

class C extends A, B {
}

A and B test() methods are inheriting to C class.

So which test() method C class will take? As A & B class test() methods are different , So here we would Facing Ambiguity.

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Frequently asked to fresh graduates.

Q152. What is the difference between yield() and sleep()?

Operating System

Ans. When a object invokes yield() it returns to ready state. But when an object invokes sleep() method enters to not ready state.

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Usually asked only to fresh graduates.

Q153. What is the initial state of a thread when it is created and started?

Ans. Ready state.

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Q154. What restrictions are placed on method overriding?

Ans. Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides. The overriding method may not throw any exceptions that may not be thrown by the overridden method.

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Q155. How does a try statement determine which catch clause should be used to handle an exception?

Core Java

Ans. When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exception is executed. The remaining catch clauses are ignored.

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Q156. Explain static blocks in Java ?

Core Java

Ans. A static initialization block is a normal block of code enclosed in braces, { }, and preceded by the static keyword. Here is an example:

static {
// whatever code is needed for initialization goes here
}

A class can have any number of static initialization blocks, and they can appear anywhere in the class body. The runtime system guarantees that static initialization blocks are called in the order that they appear in the source code.

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Q157. Explain Annotations ?

Ans. Annotations, a form of metadata, provide data about a program that is not part of the program itself. Annotations have no direct effect on the operation of the code they annotate. Annotations have a number of uses, among them:
â€¢ Information for the compiler â€” Annotations can be used by the compiler to detect errors or suppress warnings.
â€¢ Compile-time and deployment-time processing â€” Software tools can process annotation information to generate code, XML files, and so forth.
â€¢ Runtime processing â€” Some annotations are available to be examined at runtime.

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Q158. What is a finalize method ?

Core Java

Ans. finalize() method is called just before an object is destroyed.

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Recently asked in Infoview Technologies.

Q159. What is a Default Constructor ?

Core Java

Ans. The no argument constructor provided by Java Compiler if no constructor is specified.

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Q160. Whats the purpose of marker interfaces ?

Ans. They just tell the compiler that the objects of the classes implementing the interfaces with no defined methods need to be treated differently.

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Usually asked only to fresh graduates and less experienced developers.

Q161. What is a daemon thread? Give an Example ?

Ans. These are threads that normally run at a low priority and provide a basic service to a program or programs when activity on a machine is reduced. garbage collector thread is daemon thread.

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Very Frequently asked Spring question.

Q162. What is bean auto wiring?

Spring

Ans. The Spring container is able to autowire relationships between collaborating beans. This means that it is possible to automatically let Spring resolve collaborators (other beans) for your bean by inspecting the contents of the BeanFactory without using and elements.

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Q163. Explain Inner Classes ?

Core Java

Ans. The accessibility (public, protected, etc.) of the inner class is defined by the outer class.

Just like top-level classes, an inner class can extend a class or can implement interfaces.

Similarly, an inner class can be extended by other classes, and an inner interface can be implemented or extended by other classes or interfaces.

An inner class can be declared final or abstract.Inner classes can have inner classes, but you will have a hard time reading or understanding such complex nesting of classes.

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Q164. When you will synchronize a piece of your code?

Ans. When you expect your code will be accessed by different threads and these threads may change a particular data causing data corruption.

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Q165. What is connection pooling?

Database

Ans. It's a technique to allow multiple clients to make use of a cached set of shared and reusable connection objects providing access to a database or other resource.

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Q166. Difference between throw and throws ?

Core Java

Ans. throw is used to explicitly throw an exception especially custom exceptions, whereas throws is used to declare that the method can throw an exception.

We cannot throw multiple exceptions using throw statement but we can declare that a method can throw multiple exceptions using throws and comma separator.

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Q167. What is an Object ?

Core Java

Ans. Object is a run time entity whose state is stored in fields and behavior is shown via methods. Methods operate on an object's internal state and serve as the primary mechanism for object-to-object communication.

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Q168. What is a Class ?

Core Java

Ans. A class is a blue print or Mold using which individual objects are created. A class can contain fields and methods to describe the behavior of an object.

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Q169. What are use cases?

Process

Ans. It is part of the analysis of a program and describes a situation that a program might encounter and what behavior the program should exhibit in that circumstance.

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Q170. What is the difference between a break statement and a continue statement?

Core Java

Ans. Break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.

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Q171. What is the use of HashCode in objects ?

Core Java

Ans. Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc.

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Q172. What will be the output of the following code ?

String s1 = "Buggy Bread";
String s2 = "Buggy Bread";
if(s1 == s2)
System.out.println("equal 1");
String n1 = new String("Buggy Bread");
String n2 = new String("Buggy Bread");
if(n1 == n2)
System.out.println("equal 2");

Core Java

Ans. equal 1

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Q173. Which markup languages can be used in restful web services ?

Rest

Ans. XML and JSON ( Javascript Object Notation ).

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Q174. Difference between Inner and Outer Join ?

Database

Ans. Inner join is the intersection of two tables on a particular columns whereas Outer Join is the Union of two tables.

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Q175. What is a Cursor ?

Database

Ans. It's a facility that allows traversal over the records pulled from a table or combination of tables. Its like iterator in Java.

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Very Frequently asked. Favorite question in walkins and telephonic interviews. Usually among first few questions. Asked in different variants. Must know for intermediate and expert professionals.Among Top 10 frequently asked questions.

Q176. What is rule regarding overriding equals and hashCode method ?

Core Java

Ans. A Class must override the hashCode method if its overriding the equals method.

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Q177. Can we have null keys in TreeMap ?

Core Java

Ans. No, results in exception.

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Q178. What are the different types of inheritance in Hibernate ?

Hibernate

Ans. Table Per Class , Table per Sub Class , Table per Concrete Class

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Q179. What is lazy fetching in Hibernate ?

Hibernate

Ans. Lazy fetching is the technique of not loading the child objects when parent objects are loaded. By default Hibernate does not load child objects. One can specify whether to load them or not while doing the association.

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Frequently asked these days as there are major changes in Java 8.

Q180. What are new features introduced with Java 8 ?

Core Java

Ans. Lambda Expressions , Interface Default and Static Methods , Method Reference , Parameters Name , Optional , Streams, Concurrency.

Sample Code for Lambda

Sample Code for interface default

Sample Code for Optional

Sample Code for Streams

Sample Code for java.time

Sample Code for Predicate

Sample Code for Consumer

Sample Code for MapMerge

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