UST Senior Java Developer Interview Questions and Answers

Q1. Java 8, exception handling for method overriding, collections basic on HashMap , hash set, blocking queue. Transient volatile
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Q1. DESCRIBE TYPES JVM MEMORY.
Ans. 
JVM memory consists of Young Generation, Old Generation, and Permanent Generation.
• Young Generation: where new objects are allocated and aged before moving to Old Generation.

• Old Generation: where long-lived objects are stored.

• Permanent Generation: where metadata such as class definitions and method information are stored.
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Q2. DIFFERENCE BETWEEN INTERFACE AND ABSTRACT CLASS.
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Interface is a contract with no implementation, while abstract class can have some implementation.
• Interface cannot have any method implementation, while abstract class can have some method implementations.

• A class can implement multiple interfaces, but can only extend one abstract class.

• Interfaces are used to achieve multiple inheritance in Java.

• Abstract classes can have constructors, while interfaces cannot.

• Example: In...read more
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Q3. HOW TO CREATE OUR OWN IMMUTABLE CLASS? WHY IMMUTABLE CLASS
Ans. 
Immutable classes in Java are classes whose objects cannot be modified once they are created.
• Make the class final to prevent inheritance

• Make all fields private and final

• Do not provide setter methods for fields

• Ensure that any mutable objects within the class are also immutable
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Q4. WHAT IS DIFFERENCE BETWEEN COMPOSITION AND AGGREGATION ?
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Composition is a strong relationship where the child object cannot exist independently of the parent object, while aggregation is a weak relationship where the child object can exist independently.
• Composition is a 'has-a' relationship, where the child object is a part of the parent object.

• Aggregation is a 'has-a' relationship, where the child object is not a part of the parent object.

• In composition, the child object is...read more
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Q5. DIFFERENCE BETWEEN COMPARABLE AND COMPARATOR.
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Comparable is an interface used for natural ordering of objects, while Comparator is an interface used for custom ordering of objects.
• Comparable interface is implemented by the class whose objects are to be compared, while Comparator interface is implemented by a separate class.

• Comparable interface has a single method compareTo() for comparing objects, while Comparator interface has a single method compare() for custom...read more
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Q6. DIFFERENCE BETWEEN HASHMAP AND CONCURRENTHASH MAP
Ans. 
HashMap is not thread-safe while ConcurrentHashMap is thread-safe.
• HashMap is not thread-safe and can lead to ConcurrentModificationException if modified during iteration.

• ConcurrentHashMap allows concurrent read and write operations without the need for external synchronization.

• ConcurrentHashMap achieves thread-safety by dividing the map into segments, allowing multiple threads to operate on different segments concurren...read more
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Q7. DIFFERENCE BETWEEN COLLECTION AND STREAM
Ans. 
Collections store data while streams process data in a functional way.
• Collections are used to store and manage groups of objects, while streams are used to process collections of objects.

• Collections are mutable, meaning you can add, remove, or modify elements, while streams are immutable and do not change the original data.

• Streams use functional programming concepts like map, filter, and reduce to process data efficien...read more
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Q8. IN WHICH SITUATION WE USE @PRIMARY AND @ QUALIFIER ?
Ans. 
Use @Primary to specify a primary bean when multiple beans of the same type are present. Use @Qualifier to specify a specific bean when multiple beans of the same type are present.
• Use @Primary to indicate the primary bean to be used when multiple beans of the same type are present in the Spring application context.

• Use @Qualifier along with @Autowired to specify a specific bean to be injected when multiple beans of the ...read more
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Q1. Oops, Thread, Spring boot and hibernate
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Q2. JDBC vs HIBERNATE
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JDBC is a low-level API for connecting to databases in Java, while Hibernate is a high-level ORM framework that simplifies database interactions.
• JDBC requires writing SQL queries manually, while Hibernate provides an object-oriented approach to database operations.

• Hibernate handles mapping Java objects to database tables, while JDBC requires manual mapping.

• Hibernate provides caching mechanisms for improved performance,...read more
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Q3. COLLECTION FRAMEWORK
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Q1. Project Related Questions
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Java8 stream api related problems to code in notepad

Q1. Why string immutable
Ans. 
String is immutable in Java to ensure security, thread safety, and optimization.
• Immutable strings prevent accidental changes to sensitive data like passwords.

• Immutable strings allow for safe sharing of data across multiple threads.

• Immutable strings enable string pooling for memory optimization.
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Q1. Questions about spring boot annotations
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1. Basic Java
2. Code Snippet
3. Microservices

Q1. Questions related to Multi threading, Exception Handling, Streams, Springboot annotations, Microservices were asked.
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