VELAN IT Solutions Data Engineer 1 Interview Questions and Answers

OOPs concepts in Java are the fundamental principles of object-oriented programming.

• Encapsulation: wrapping data and code into a single unit

• Inheritance: creating new classes from existing ones

• Polymorphism: using a single interface to represent multiple types

• Abstraction: hiding implementation details from the user

• Examples: class, object, inheritance, polymorphism, encapsulation

Stack is a LIFO data structure while Queue is a FIFO data structure.

• Stack follows Last In First Out (LIFO) principle while Queue follows First In First Out (FIFO) principle.

• Stack has two main operations: push and pop while Queue has two main operations: enqueue and dequeue.

• Stack is used in recursive function calls, undo/redo operations, and backtracking while Queue is used in breadth-first search, printing tasks in ord...read more

SQL query to find second highest salary in database

• Use ORDER BY and LIMIT to get the second highest salary

• Assume ties are allowed and use DISTINCT

Method overloading is having multiple methods with the same name but different parameters. Method overriding is having a method in a subclass with the same name and parameters as a method in its superclass.

• Method overloading is done within the same class while method overriding is done in different classes (subclass and superclass).

• Method overloading is achieved by changing the number of parameters or the data type of ...read more

The parent class of all classes in Java is the Object class.

• All classes in Java implicitly extend the Object class.

• The Object class provides basic methods such as toString(), equals(), and hashCode().

• Any class can override these methods to provide custom implementations.

• Example: public class MyClass extends Object { ... }

• Example: Object obj = new MyClass();

SQL databases are relational and use structured query language, while NoSQL databases are non-relational and use various data models.

• SQL databases are based on a fixed schema, while NoSQL databases are schema-less.

• SQL databases use tables to store data, while NoSQL databases use various data models like key-value, document, columnar, or graph.

• SQL databases are better suited for complex queries and structured data, whil...read more