30 Essential Java and Spring Interview Questions with One-Line Answers

If you’re preparing for a Java and Spring interview, it’s crucial to master theory-based questions to demonstrate your understanding of core concepts. Here are 30 common questions with concise one-line answers to help you get started.

Java Interview Questions

1. What is the Java Virtual Machine (JVM)?
   Answer: A runtime environment that executes Java bytecode.
2. What is the difference between JDK, JRE, and JVM?
   Answer: JDK is for development, JRE is for running applications, and JVM is the engine that executes bytecode.
3. What are Java’s access modifiers?
   Answer: public, protected, default (no modifier), and private.
4. What is the difference between final, finally, and finalize?
   Answer: final prevents modification, finally is for cleanup in try-catch, and finalize is used for garbage collection.
5. What is the purpose of the transient keyword?
   Answer: Marks a variable to be excluded during serialization.
6. What is a marker interface?
   Answer: An interface with no methods or fields, used to signal metadata (e.g., Serializable).
7. What is the difference between == and equals()?
   Answer: == checks reference equality, while equals() checks value equality.