Servtek It Java Developer Interview Questions and Answers

Q1. Diff between abstract class and interface
Ans. 
Abstract class can have both abstract and non-abstract methods, while interface can only have abstract methods.
• Abstract class can have constructor, fields, and methods, while interface cannot have any of these.

• A class can extend only one abstract class, but can implement multiple interfaces.

• Abstract classes are used to define a common behavior among subclasses, while interfaces are used to define a contract for classes...read more
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Q2. Explain about handler methods
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Handler methods in Java are methods that are responsible for handling incoming requests and generating responses.
• Handler methods are typically defined in classes annotated with @Controller or @RestController.

• These methods are mapped to specific URLs using @RequestMapping or other mapping annotations.

• Handler methods can have parameters such as HttpServletRequest, HttpServletResponse, or model attributes.

• The return value...read more
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Q1. Prime number program
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A program to check if a given number is prime or not.
• Create a function to check if a number is prime by iterating from 2 to the square root of the number.

• If the number is divisible by any number other than 1 and itself, it is not prime.

• Handle edge cases like 0, 1, and negative numbers separately.
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Q2. 3rd highest salary employee
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To find the 3rd highest salary employee, we can use a SQL query with the 'LIMIT' and 'OFFSET' keywords.
• Use a SQL query to select distinct salaries in descending order

• Use 'LIMIT 1 OFFSET 2' to get the 3rd highest salary

• Join this result with the employee table to get the employee details
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Aptitude questions and some questions from PostgreSQL.

Q1. Java fundamental questions?
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Q2. Collection Framework.
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Q3. 2-3 easy to medium Coding Questions.
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Q4. Questions from Object oriented programming in Java?
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Q5. Implementation of HashMap , LinkedList, HashSet, Heap?
Ans. 
HashMap, LinkedList, HashSet, and Heap are data structures commonly used in Java for storing and organizing data.
• HashMap: key-value pairs, uses hashing to store and retrieve elements efficiently (e.g. HashMap)

• LinkedList: linear data structure, elements are stored in nodes with pointers to the next node (e.g. LinkedList)

• HashSet: collection of unique elements, uses hashing to ensure uniqueness (e.g. Hash...read more
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Q1. Comparable vs Comparator
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Comparable is an interface used for natural ordering, while Comparator is used for custom ordering in Java.
• Comparable interface is used to define the natural ordering of objects. It is implemented by the class whose objects are to be sorted.

• Comparator interface is used to define custom ordering of objects. It is implemented by a separate class that compares objects based on specific criteria.

• Example: Sorting a list of ...read more
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Q2. Difference between List and Set

Ans. 

List allows duplicate elements and maintains insertion order, while Set does not allow duplicates and does not maintain order.

• List can contain duplicate elements, Set cannot

• List maintains insertion order, Set does not guarantee order

• List is implemented by classes like ArrayList, LinkedList, Set is implemented by classes like HashSet, TreeSet

• Example: List list = new ArrayList<>(); Set set = new HashSet<>();

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