Java Interview Question – JDK, JRE and JVM

Q1. (Asked in TCS): What is the JVM in Java?

JVM stands for Java Virtual Machine. It is responsible for:

• Running Java bytecode (.class files)
• Converting bytecode to machine code
• Providing platform independence
  It also handles memory management, garbage collection, and security.

---

Q2. (Asked in Infosys): What is JRE and how is it different from JVM?

• JRE (Java Runtime Environment) is a package that provides the libraries and JVM needed to run Java programs.
• JVM is a part of JRE that actually executes the bytecode.
  So, JRE = JVM + Libraries + Other files needed to run Java apps.

---

Q3. (Asked in Capgemini): What is the JDK in Java?

JDK stands for Java Development Kit. It is used to develop Java applications.
It includes:

• JRE (to run the program)
• Development tools like javac (compiler), java (launcher), and debugging tools.

---

Q4. (Asked in Cognizant): Can you explain the difference between JDK, JRE, and JVM?

Component	Purpose	Includes
JVM	Executes bytecode	Part of JRE
JRE	Runs Java programs	JVM + Libraries
JDK	Develops Java programs	JRE + Tools like compiler

---

Q5. (Asked in Wipro): Is JDK required to run a Java program?

No, JDK is not required just to run a Java program.
You only need JRE to run a program.
JDK is required when you want to compile and develop Java code.

---

Q6. (Asked in HCL): What is the role of the Java compiler in the JDK?

The Java compiler (javac) is a tool in the JDK that converts Java source code (.java files) into bytecode (.class files), which the JVM can understand and execute.

---

Q7. (Asked in Accenture): What is bytecode in Java?

Bytecode is the intermediate code generated by the Java compiler.
It is a .class file that the JVM executes, making Java programs platform-independent.

---

Q8. (Asked in MAANG-level mock interview – Meta): Why is Java considered platform-independent but JVM is platform-dependent?

• Java is platform-independent because bytecode can run on any system with a JVM.
• JVM is platform-dependent because each OS has its own implementation of JVM.

---

Q9. (Asked in Zoho): Can you install JRE separately from JDK? When would you do that?

Yes, JRE can be installed separately if you only need to run Java applications (e.g., running Java-based tools or games).
JDK is needed only if you want to write and compile Java programs.

---

Q10. (Asked in Byju’s): What happens when you type java HelloWorld in the terminal?

• The java command uses the JVM to load the HelloWorld.class file.
• The JVM calls the main() method and starts executing the code.
• The program runs using resources provided by the JRE.