People Tech Group Technical Lead Interview Questions and Answers

Promise is a one-time operation that resolves or rejects, while Observable is a stream of multiple values over time.

• Promise is eager, Observable is lazy

• Promise can only handle a single value, Observable can handle multiple values

• Promise is not cancellable, Observable can be unsubscribed

• Promise is not composable, Observable is composable

• Example: Promise resolves with a single value like fetching data from an API, Observ...read more

Pure popes are those who have never been married, while impure popes are those who were previously married.

• Pure popes have never been married, following the tradition of celibacy in the Catholic Church.

• Impure popes were previously married before becoming pope, which is rare but has happened in history.

• Examples of impure popes include Pope Adrian II and Pope Clement IV.

Java 8 features include lambda expressions, functional interfaces, streams, and default methods.

• Lambda expressions allow you to write code in a more concise and readable way.

• Functional interfaces enable the use of lambda expressions.

• Streams provide a way to work with collections of objects in a functional style.

• Default methods allow interfaces to have method implementations.

• Examples: Using lambda expressions to iterate...read more

Map applies a function to each element in a collection, while flatMap applies a function that returns a collection and flattens the result. Function is used to transform input into output, Predicate is used to test a condition.

• Map transforms each element in a collection using a function

• FlatMap transforms each element in a collection using a function that returns a collection and flattens the result

• Function is used to t...read more

Use stream API to find sum of even numbers from a list

• Use filter to get only even numbers

• Use mapToInt to convert stream to IntStream

• Use sum() to get the sum of even numbers

Liskov's substitution principle states that objects of a superclass should be replaceable with objects of its subclasses without affecting the program's correctness.

• Subtypes must be substitutable for their base types

• Derived classes should be able to extend the functionality of base classes without changing their behavior

• Violating this principle can lead to unexpected behavior and errors in the program

Switch-case can break the Open/Closed Principle by requiring modification of existing code for new cases.

• Switch-case statements violate the Open/Closed Principle, which states that classes should be open for extension but closed for modification.

• Adding a new case to a switch statement requires modifying the existing code, violating the principle of not modifying existing code.

• Instead of using switch-case, consider usin...read more

Different kinds of DB joins include inner join, outer join, left join, and right join.

• Inner join: Returns rows when there is at least one match in both tables.

• Outer join: Returns all rows when there is a match in one of the tables.

• Left join: Returns all rows from the left table and the matched rows from the right table.

• Right join: Returns all rows from the right table and the matched rows from the left table.