Perennial Systems Senior Java Developer Interview Questions and Answers for Experienced

String decoding- given string i2s t2e1st ne3w1 Th1is , to This is new test (Hint- word based on sum of numbers in that)

Q1. OOP, Spring, Kafka, Docker,
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Q2. Find the occurence of first non-repeating char in a string
Ans. 
Use a hashmap to store the frequency of each character and then iterate through the string to find the first non-repeating character.
• Create a hashmap to store the frequency of each character in the string.

• Iterate through the string and update the frequency in the hashmap.

• Iterate through the string again and return the first character with frequency 1.
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Q3. With stream API, find employees with salary greater than 50000 and arrange it in descending order. using streams find average of numbers in a list
Ans. 
Use stream API to filter employees by salary and find average of numbers in a list.
• Filter employees with salary > 50000 and sort in descending order using stream API

• Calculate average of numbers in a list using stream API
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Q4. OOP find error or output on try catch finally block, one on final variable
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Q5. What is broker, message, corelation id in kafka
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In Kafka, a broker is a server that stores and manages the message data, a message is a unit of data sent through Kafka, and a correlation id is used to link related messages.
• A broker in Kafka is a server that stores and manages the message data.

• A message in Kafka is a unit of data sent through Kafka from a producer to a consumer.

• A correlation id in Kafka is used to link related messages together, allowing for tracking...read more
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Q6. Microservices- distributed tracing
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Q7. API gateway responsibilities
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API gateway is responsible for managing, securing, and optimizing API traffic between clients and services.
• Acts as a single entry point for all API requests

• Handles authentication and authorization

• Provides rate limiting and throttling

• Logs and monitors API traffic

• Transforms requests and responses

• Caches responses for improved performance
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Q8. Exception handling
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Q9. Bean life cycle
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Q1. Junit how to check if object is null
Ans. 
Use assertNotNull() method from Junit to check if an object is null.
• Use assertNotNull() method from Junit library

• Pass the object as a parameter to assertNotNull() method

• If the object is null, the test will fail
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Q2. Write code for time conversion- string "10:00 AM" if added 10 in that, op 8 pm
Ans. 
Convert time string by adding 10 hours and display in 12-hour format
• Split the input string into hours and minutes

• Convert the hours to 24-hour format and add 10 hours

• Handle the case where the result goes past 12 hours

• Convert the result back to 12-hour format and display
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Q3. Functional interface, method reference, spring beans- can have more than one with the same name
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Q4. Class object vs bean
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Class object is a blueprint for creating objects, while a bean is a Java object that is serializable, has a no-argument constructor, and allows access to properties using getter and setter methods.
• Class object is a template for creating instances of a class, defining its properties and methods.

• Bean is a Java object that follows specific conventions like being serializable, having a no-argument constructor, and providin...read more
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Q5. Apring annotations, how to exclude class configuration
Ans. 
Use @ComponentScan annotation with excludeFilters to exclude class configuration in Spring
• Use @ComponentScan annotation with excludeFilters parameter to exclude specific classes from component scanning

• Specify the classes to be excluded using TypeFilter implementations like AnnotationTypeFilter or AssignableTypeFilter

• Example: @ComponentScan(basePackages = {"com.example"}, excludeFilters = @ComponentScan.Filter(type = Fi...read more
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