Top 10 Java Questions in 2026
Top 10 Java Questions in 2026 uses verified RivoHire qbank answers. Start with the strongest short answer, then review tradeoffs, scenarios, mistakes, and interview wording.
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Question Collection
Quick outcome
By the end of this guide, you will:
- A Java change causes slower responses after traffic increases. I would isolate the hot path, apply the smallest reversible fix, and verify the result with latency, error rate, and rollback readiness.
- A Spring Boot change causes slower responses after traffic increases. I would isolate the hot path, apply the smallest reversible fix, and verify the result with latency, error rate, and rollback readiness.
- A Java change causes slower responses after traffic increases. I would isolate the hot path, apply the smallest reversible fix, and verify the result with latency, error rate, and rollback readiness.
- A Spring Boot change causes slower responses after traffic increases. I would isolate the hot path, apply the smallest reversible fix, and verify the result with latency, error rate, and rollback readiness.
Coding question collection
Interview Questions With Code Practice
Each question includes the prompt, interview explanation, language tabs, a code-editor style solution, and time and space complexity notes.
Difficulty Distribution
1. What is the difference between JDK, JRE, and JVM?
JDK is used to develop Java applications, JRE runs Java applications, and JVM executes Java bytecode.
JDK is used to develop Java applications, JRE runs Java applications, and JVM executes Java bytecode. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
2. What is auto-configuration in Spring Boot?
Auto-configuration creates beans based on classpath, properties, and existing beans to reduce manual setup.
Auto-configuration creates beans based on classpath, properties, and existing beans to reduce manual setup. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
3. How does HashMap work internally in Java?
HashMap stores entries in buckets by hash code, resolves collisions, resizes by load factor, and may treeify dense buckets.
HashMap stores entries in buckets by hash code, resolves collisions, resizes by load factor, and may treeify dense buckets. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
4. How does dependency injection work in Spring?
Spring creates and wires beans into dependent classes, usually through constructor injection.
Spring creates and wires beans into dependent classes, usually through constructor injection. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
5. What is the difference between @Controller and @RestController?
@Controller returns views by default, while @RestController combines @Controller and @ResponseBody for API responses.
@Controller returns views by default, while @RestController combines @Controller and @ResponseBody for API responses. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
6. What is the difference between checked and unchecked exceptions?
Checked exceptions must be declared or handled, while unchecked exceptions extend RuntimeException and are not enforced by the compiler.
Checked exceptions must be declared or handled, while unchecked exceptions extend RuntimeException and are not enforced by the compiler. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
7. How does the Java memory model affect concurrency?
The Java memory model defines visibility, ordering, happens-before relationships, and safe publication between threads.
The Java memory model defines visibility, ordering, happens-before relationships, and safe publication between threads. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
8. How do you handle exceptions in Spring Boot APIs?
Use @ControllerAdvice and exception handlers to map domain and validation errors to consistent HTTP responses.
Use @ControllerAdvice and exception handlers to map domain and validation errors to consistent HTTP responses. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
9. How do Spring profiles work?
Profiles activate environment-specific beans and configuration for development, testing, staging, or production.
Profiles activate environment-specific beans and configuration for development, testing, staging, or production. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
10. What is the difference between String, StringBuilder, and StringBuffer?
String is immutable, StringBuilder is mutable and unsynchronized, and StringBuffer is mutable and synchronized.
String is immutable, StringBuilder is mutable and unsynchronized, and StringBuffer is mutable and synchronized. I would also mention the tradeoff, the failure mode, and how I would test it in a real service.
Mention edge cases before writing code, then finish with time and space complexity.
FAQ
What is the difference between JDK, JRE, and JVM?
JDK is used to develop Java applications, JRE runs Java applications, and JVM executes Java bytecode. In an interview, support it with one tradeoff and one production example.
What is auto-configuration in Spring Boot?
Auto-configuration creates beans based on classpath, properties, and existing beans to reduce manual setup. In an interview, support it with one tradeoff and one production example.
How does HashMap work internally in Java?
HashMap stores entries in buckets by hash code, resolves collisions, resizes by load factor, and may treeify dense buckets. In an interview, support it with one tradeoff and one production example.
How does dependency injection work in Spring?
Spring creates and wires beans into dependent classes, usually through constructor injection. In an interview, support it with one tradeoff and one production example.
What is the difference between @Controller and @RestController?
@Controller returns views by default, while @RestController combines @Controller and @ResponseBody for API responses. In an interview, support it with one tradeoff and one production example.
What is the difference between checked and unchecked exceptions?
Checked exceptions must be declared or handled, while unchecked exceptions extend RuntimeException and are not enforced by the compiler. In an interview, support it with one tradeoff and one production example.
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