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Q361. Explain Java 8 concurrency mechanism.

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Q362. If Table A has 0 records and Table B has 50 records , how many records will the equi join of Table generate ?

SQL

Ans. 0 records

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Q363. If Table A has 100 records and Table B has 50 records , how many records will the right join of Table A with Table B generate ?

SQL

Ans. 50 records

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Q364. If Table A has 100 records and Table B has 50 records , how many records will the left join of Table A with Table B generate ?

SQL

Ans. 100 records

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Q365. If Table A has 100 records and Table B has 50 records , how many records will the equi join of Table generate ?

SQL

Ans. It depends on the join condition.

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Q366. Write a Program to find age by birth date ?

Core Java

Ans. LocalDate today = LocalDate.now();
LocalDate birthday = LocalDate.of(1960, Month.JANUARY, 1);
Period p = Period.between(birthday, today); //Now access the values as below
System.out.println(period.getDays());
System.out.println(period.getMonths());
System.out.println(period.getYears());

Sample Code for LocalDate

Sample Code for Period

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Q367. Difference between ApplicationContext and BeanFactory ?

Spring

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Q368. Difference between constructor and setter injection ?

Spring

Ans. 1. In Setter Injection, partial injection of dependencies can possible, means if we have 3 dependencies like int, string, long, then its not necessary to inject all values if we use setter injection. If you are not inject it will takes default values for those primitives1. In constructor injection, partial injection of dependencies cannot possible, because for calling constructor we must pass all the arguments right, if not so we may get error

2. Setter Injection will overrides the constructor injection value, provided if we write setter and constructor injection for the same property [i already told regarding this, hope you remember ] But, constructor injection cannot overrides the setter injected values

3. If we have more dependencies for example 15 to 20 are there in our bean class then, in this case setter injection is not recommended as we need to write almost 20 setters right, bean length will increase. In this case, Constructor injection is highly recommended, as we can inject all the dependencies with in 3 to 4 lines [i mean, by calling one constructor]

4. Setter injection makes bean class object as mutable [We can change ] .Constructor injection makes bean class object as immutable [We cannot change ]

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Q369. Why doesn't java support operator overloading ?

Core Java

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Q370. Can a source file contain more than one class declaration ?

Core Java

Ans. Yes, but only one of them can be declared public.

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Q371. How do we define constant variables in Java ?

Core Java

Ans. By using static and final modifiers.

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Q372. Which java package is loaded by default and hence doesn't require an explicit import statement ?

Core Java

Ans. java.lang

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Q373. What is the problem we could face if we be very liberal with importing classes even if we are not using them ? For example

import java.util.*;
import java.io.*;

Core Java

Ans. It makes application little heavy as we are importing classes that aren't required.

It creates class name conflicts as similar name classes might be available across different packages. In case of such conflicts, we will have to specify the package name with the class name at the time of it's usage.

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Q374. What does import java.util.* means in java ?

Core Java

Ans. It means import all the classes and interfaces within java.util package and make them available to use within the current class or interface. This is shorthand wild card annotation for importing all classes within a particular package. This won't import the classes within the sub packages of java.util.

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Q375. Can we compile and execute a Java class without main method ?

Core Java

Ans. No without main method can not be executed it will throw an error illegal start of type. Main method is the entry point of application.

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Q376. What is the difference between Stack and Queue ?

Data Structures

Ans. Stack is based on Last in First out (LIFO) principle while a queue is based on FIFO (First In First Out) principle.

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Q377. Are char,String and Char data types in java ?

Core Java

Ans. char is a primitive data type. String is a class. Char is a wrapper class for primitive char.

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Q378. Is String a Data type in Java ?

Core Java

Ans. String is not a primitive type in java. Anything defined within double quotes like "abc" is an object of String class.

Sample Code for String

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Q379. What is the difference between JDBC, Hibernate and ODBC ?

Database

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Q380. What is a ternary operator ?

Database

Ans. Ternary operator , also called conditional operator is used to decide which value to assign to a variable based on a Boolean value evaluation. It is used as

condition ? value1 : value2

For example

int y = (x > 0) ? x:0; // assign x if it's greater than 0, else assign 0

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Q381. What is an infinite loop ?

Core Java

Ans. Infinite loop is a programming condition wherein the control goes into an infinite loop because the loop termination condition can never be met. For example -

for(int x=1;x>0;x++){
}

in this loop, with each increment the condition x > 0 will remain true till infinity.

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Q382. What are the different types of loops in Java ?

Core Java

Ans. for, while and do while

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Q383. Give an example of how Object Oriented Programming Concepts can be implemented.

Design

Ans. You can implement encapsulation in Java by keeping the fields (class variables) private and providing public getter and setter methods to each of them. Java Beans are examples of fully encapsulated classes. Encapsulation in Java: Restricts direct access to data members (fields) of a class.

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Q384. Solve the producer and consumer problem

Operating System

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Q385. Explain OOPs

or

Explain OOPs Principles

or

Explain OOPs Concepts

or

Explain OOPs features

or

Tell me something about OOPs

Core Java

Ans. OOPs or Object Oriented Programming is a Programming model which is organized around Objects instead of processes. Instead of a process calling series of processes, this model stresses on communication between objects. Objects that all self sustained, provide security by encapsulating it's members and providing abstracted interfaces over the functions it performs. OOP's facilitate the following features

1. Inheritance for Code Reuse
2. Abstraction for modularity, maintenance and agility
3. Encapsulation for security and protection
4. Polymorphism for flexibility and interfacing

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Usually asked in relation to casting and ClassCastException.

Q386. What is instanceOf operator ? Explain it's use ?

Core Java

Ans. The operator instanceOf is used to verify if the specified object is the instance of specified class or interface.

Syntax if(x instanceOf ABC)

where x is an object reference and ABC could be a class name or interface name. The above statement will be true if x holds an object that is an instance of ABC or any of the child class of ABC or if x holds an object that implements ABC.

instanceOf operator is used to verify in case of downcasting. For ex -

DerivedClass extends BaseClass

x is the reference of BaseClass but holds DerivedClass object ( Polymorphism )

There is an operation that is defined in Derived Class, let's say derivedClassMethod()

We cannot call derivedClassMethod() directly using x as x is reference of BaseClass and not DerivedClass and hence can only access methods that are defined in BaseClass and overridden in derived class.

Though we can cast it to DerivedClass as following
((DerivedClass)x).derivedClassMethod();

But it may throw ClassCastException in case x doesn't hold an instance of DerivedClass at that point.

So before casting it to DerivedClass we may like to make sure that it is an instance of DerivedClass and hence won't throw ClassCastException.

So we make a check for it

if(x instanceOf DerivedClass) {
((DerivedClass)x).derivedClassMethod();
}

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Very frequently asked. Usually among very first few questions.

Q387. Define encapsulation in Java ?

Core Java

Ans. Encapsulation is a feature of OOP's that binds the data and it's associated methods together as a single unit and facilitate protection and data hiding by providing minimal interface to outside. For example - member variables are declared private and are accessed through public methods. Moreover we have private methods that can only be used internally and hence providing minimal interface to outside class through use of public methods.

Sample Code for encapsulation

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Q388. What is meant by "Vector is synchronized and ArrayList isn't " ?

Core Java

Ans. It means that only 1 thread can access have access to Vector at a time and no parallel access is allowed whereas Array List allows parallel access by multiple threads.

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Q389. How would you explain the statement "Java Programs are collection of objects" ?

Core Java

Ans. Java Programs are collection of objects that communicates with each other to get a task accomplished. To add to those objects, there are common spaces ( static i.e common for objects belonging to a class ) that are used too.

We can visualize objects as departments of an organization in real world. Just like Task gets initiated in one department and then files are moved across different departments to get work done. In a similar fashion, a task is initiated in one object ( having main method ) and then information ( through POJOs / DTOs ) is moved across objects to accomplish a task.

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Q390. How can we hide a class in Java ?

Core Java

Ans. By encapsulating it within another class and declaring it private. In such a case, it will only be accessible through parent class or parent class object.

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