10+ Interview Questions and Answers

Hash map is a data structure that stores key-value pairs and allows fast retrieval of values based on keys.

• Hash map uses hashing to store and retrieve values based on keys

• It allows null values and null keys

• It is not synchronized and not thread-safe

• Example: HashMap map = new HashMap<>();

• map.put("apple", 1); int value = map.get("apple");

List of SQL languages and their brief explanation

• SQL (Structured Query Language) is a standard language for managing relational databases

• T-SQL (Transact-SQL) is a proprietary extension of SQL used by Microsoft SQL Server

• PL/SQL (Procedural Language/Structured Query Language) is Oracle Corporation's proprietary extension of SQL

• MySQL is an open-source relational database management system that uses SQL

• PostgreSQL is an open-source object-relational database management system that...read more

Super key is a set of attributes that uniquely identifies a record, while foreign key is a reference to a primary key in another table.

• Super key is a combination of one or more attributes that uniquely identifies a record in a table.

• Foreign key is a field in a table that refers to the primary key of another table.

• Super key can have additional attributes that are not necessary for uniqueness.

• Foreign key establishes a relationship between two tables.

• Example: In a database of st...read more

Memory management and hash map are important concepts in Java programming.

• Memory management is the process of allocating and deallocating memory in a program.

• Java uses automatic memory management through garbage collection.

• Hash map is a data structure that stores key-value pairs and uses hashing to retrieve values efficiently.

• Java's HashMap class implements the Map interface and provides constant-time performance for basic operations.

• It is important to properly manage memory ...read more

Primary key uniquely identifies a record while candidate key can also uniquely identify a record but may not be chosen as primary key.

• Primary key is a column or set of columns that uniquely identifies each record in a table

• Candidate key is a column or set of columns that can also uniquely identify each record in a table

• A table can have multiple candidate keys but only one primary key

• Primary key cannot have null values while candidate key can have null values

• Example: In a tabl...read more

List of SQL languages

• MySQL

• Oracle

• PostgreSQL

• Microsoft SQL Server

• SQLite

Exception handling in Java allows for the handling of errors and exceptions that may occur during program execution.

• Java provides try-catch blocks to handle exceptions.

• The try block contains the code that may throw an exception.

• The catch block catches and handles the thrown exception.

• Multiple catch blocks can be used to handle different types of exceptions.

• The finally block is optional and is executed regardless of whether an exception occurs or not.

• Exceptions can also be thr...read more

Memory management in Java involves automatic garbage collection and manual memory allocation.

• Java uses automatic garbage collection to free up memory

• Developers can manually allocate memory using the 'new' keyword

• Java also has a 'finalize' method to clean up resources before garbage collection

• Memory leaks can occur if objects are not properly released

Exceptional handling in Java is a mechanism to handle runtime errors and prevent program crashes.

• Java provides try-catch blocks to handle exceptions

• Multiple catch blocks can be used to handle different types of exceptions

• Finally block is used to execute code regardless of whether an exception is thrown or not