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

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Q271. Explain debugging

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Q272. What is an Interface ?

Core Java

Ans. The interface is a mechanism to achieve abstraction. Interfaces can have abstract methods and variables. It cannot have a method body.

Sample Code for interface

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Q273. What is composition ?

Core Java

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Sample Code for composition

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Q274. What is Overriding ?

Core Java

Ans. Overriding refers to the Methods with same name and parameters, such that the later over rides the former method.

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Q275. What is abstraction ?

Core Java

Ans. The process of hiding the implementation details from the user and providing only functionality.

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Q276. Can we modify a list while iterating it ?

Core Java

Ans. No,we cannot.I t will give concurrentModificationExceptin error. It can be resolved by using ConcurrentClasses like ConcurrentHashMap,CopyOnWriteArrayList,BlockingQueue etc which are fail-safe and wont give exception.

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Q277. How is RDBMS different from DBMS ?

Database

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Q278. Explain Binary Search

Algorithm

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Q279. What is the use of Log4j ?

Logging

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Q280. What are the different delivery policies in Apache Kafka ?

Apache Kafka

Ans. Exactly once , At least once , At max once

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Q281. Which spring boot version are you working with ?

Spring Boot

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Q282. Suppose we make an api call using multithreading, How would you design to make sure that we have received response for all threads before exiting the main thread ?

Design

Ans. We can use HashMap for tracking response status for all threads. We can wait every n second by using Thread.sleep and exit the main thread only once we have received response for all threads.

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Q283. Difference between static and dynamic binding ?

Design

Ans. Static binding happens at the compile time whereas dynamic binding happens at runtime.

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Q284. Write a Program to print a pattern ?

Core Java

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Q285. Please explain with example different types of testing ?

Testing

Ans. Unit Testing ( Junits )
Integration Testing ( Testing overall flow by calling the entry method or by calling the service end point )
Manual Testing ( End to End Manual User Testing, they way eventually it will be used by end users )
Automation Testing ( Machine replication of end to end testing )

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Q286. How to calculate string length without using inbuilt function

Core Java

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Q287. Write code to sort an array.

Algorithm

Ans. https://www.geeksforgeeks.org/arrays-sort-in-java-with-examples/

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Q288. How to sort objects based on one of the field ?

Core Java

Ans. Using comparable and comparator and sorted collections like TreeSet or TreeMap.

or

use stream api from java 8 onwards which internally refers to comparable and comparator through lambda expressions

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Q289. What are custom annotations and How can we create one ?

Core Java

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Q290. What is the difference between scope and access modifiers ?

Core Java

Ans. Scope modifiers changes the scope of a particular element or a method. For ex - static changes the scope of that of class and not of object.

Access modifiers changes the access priviledges of a particular element or a method. For ex - private , public etc.

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Q291. Why Java has final class ?

Core Java

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Q292. How does multi threading improve performance ?

Core Java

Ans. Every process in it's timeline require different resources. Utilization of resources can be optimized when they are shared among different processes or threads. When one thread is sleeping waiting for a peripheral to complete (e.g. a disk write, or a key press from the keyboard), other threads can continue using processor time and hence would lead to better usage of resources.

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Q293. Can we change the size of array once created ?

Core Java

Ans. No. Arrays cannot resize dynamically.

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Q294. Tell something about Sleep method.

Core Java

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Q295. Have you ever worked on migrating AWS services and databases from one account to another ?

Amazon Web Services (AWS)

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Q296. Difference between git init and git clone ?

Git

Ans. "git init" creates an empty repository or can make an existing directory a git repository while "git clone" first internally calls "git init" to create an empty git repository and then copy the data from the specified remote repository.

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Q297. Can you tell me any 10 unix command you have worked with ?

Unix

Ans. grep, ls, kill, vi , scp , wget,telnet, zip, unzip,mv,cp

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Q298. Difference between List and ArrayList ?

Core Java

Ans. List is an interface whereas ArrayList is an implementation of List.

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Q299. What is the relationship between Base Class and Abstract Class ?

Core Java

Ans. Abstract Class is a class that's only allowed to be a Base class for it's usage. It can never be instantiated on it's own.

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Q300. difference between ArrayList and array ?

Core Java

Ans. ArrayList is a variable length collection class whereas arrays are fixed length primitive structure.

We can use generics with arraylist but not with arrays.

We can store primitive data types within arrays but can't with ArrayList. In ArrayList that needs to be converted to Wrapper objects.

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