Blackrock Java Engineer Interview Questions and Answers

Q1. 1. Diff between static keyword and final keyword 2. Different ways of creating thread and which approach is better 3. Pgm to find min word and max word in a sentence
Ans. 
The questions are related to Java programming and do not involve the medical field or puzzles.
• The static keyword is used to declare a variable or method that belongs to the class itself, rather than an instance of the class.

• The final keyword is used to declare a constant value or to prevent a variable, method, or class from being modified or extended.

• Different ways of creating threads in Java include extending the Thre...read more
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Q1. 1, What are the purposes of api gateway other then authentication 2. how circut breaker works 3. What is saga design pattern 4. What is primary and secondary caching
Ans. 
API gateway serves as a central entry point for all client requests, providing various functionalities beyond authentication.
• API gateway acts as a reverse proxy, routing requests to appropriate microservices.

• It can handle request/response transformation, protocol translation, and payload encryption/decryption.

• API gateway can implement rate limiting, throttling, and caching to improve performance.

• It enables service disc...read more
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Q1. What is hashmap
Ans. 
HashMap is a data structure in Java that stores key-value pairs and allows fast retrieval of values based on keys.
• HashMap implements the Map interface in Java

• It allows null keys and values

• Keys in a HashMap must be unique

• Example: HashMap map = new HashMap<>()
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Q2. Internal Working of hashmap
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HashMap is a data structure that stores key-value pairs and uses hashing to efficiently retrieve values.
• HashMap internally uses an array of linked lists to store key-value pairs.

• When a key-value pair is added, the key is hashed to determine the index in the array where it will be stored.

• If multiple keys hash to the same index, a linked list is used to handle collisions.

• HashMap uses the hashCode() method of keys to calc...read more
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Q3. Compare Throw vs Throws
Ans. 
Throw is used to explicitly throw an exception in a method, while Throws is used to declare the exceptions that a method may throw.
• Throw is used within a method to throw an exception explicitly.

• Throws is used in the method signature to declare the exceptions that the method may throw.

• Throw is followed by an instance of Throwable class, while Throws is followed by the exception class names separated by commas.

• Example: t...read more
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Q4. Array vs Arraylist
Ans. 
Arrays are fixed in size, while ArrayLists can dynamically resize. ArrayLists provide more flexibility and functionality.
• Arrays have a fixed size, while ArrayLists can dynamically resize.

• ArrayLists can easily add, remove, or modify elements, while arrays require manual shifting of elements.

• Arrays use [] syntax for declaration and initialization, while ArrayLists use the ArrayList class from the Java Collections framewo
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Q5. Arraylist vs LinkedList/Vector
Ans. 
ArrayList is resizable array implementation, LinkedList is doubly linked list implementation, Vector is synchronized version of ArrayList.
• ArrayList is faster for accessing elements, LinkedList is faster for adding/removing elements in middle.

• ArrayList uses less memory than LinkedList due to contiguous memory allocation.

• Vector is thread-safe but slower than ArrayList due to synchronization overhead.
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Q6. Write a code for Iterate hashmap using iterator
Ans. 
Iterate through a hashmap using an iterator in Java
• Create an iterator using the entrySet() method of the hashmap

• Use a while loop to iterate through the hashmap entries

• Access the key and value of each entry using the getKey() and getValue() methods
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Q1. Sort list of employee using stream concept and comparator based on employee number.
Ans. 
Sort list of employees by employee number using streams and comparator.
• Use Stream API to convert list to stream

• Use Comparator to compare employee numbers

• Use sorted() method to sort the stream based on comparator
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Q2. Thread life cycle
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Aptitude test with Java MCQ questions

Basic programs in Java

Q1. Salary discussion
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Q1. DSA Collection Spring boot Java 8
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Q1. Oops, Multithreading,DSA,Design Pattern
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Q1. What are java solid principles
Ans. 
Java SOLID principles are a set of design principles that help in creating maintainable and scalable software.
• S - Single Responsibility Principle: A class should have only one reason to change.

• O - Open/Closed Principle: Software entities should be open for extension but closed for modification.

• L - Liskov Substitution Principle: Subtypes must be substitutable for their base types.

• I - Interface Segregation Principle: Cli...read more
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Q2. How does Hashmap works internally
Ans. 
HashMap is an implementation of Map interface that stores key-value pairs using a hash table.
• HashMap uses hashing to store and retrieve elements.

• It uses an array of linked lists to handle collisions.

• The hash code of the key is used to determine the index of the array.

• If multiple keys have the same hash code, they are stored in the same linked list.

• When retrieving a value, the hash code is used to find the correct linke...read more
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Q3. Covered questions on java, spring, react
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There were 2 questions and I was supposed to write the code inside the function but the input to the function is not given correctly. Instead of giving a list to sort, I was given a single value for a function to sort.