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Core Java Interview Questions
Last Updated : 26 May, 2026
title: Core Java Interview Questions
Interview Questions265 words10 headingsTables includedExamples included
title: Core Java Interview Questions description: Top Core Java interview questions with detailed answers
Q1. Java kya hai?
Java ek high-level, object-oriented, platform-independent programming language hai. Sun Microsystems ne 1995 mein develop kiya. "Write Once, Run Anywhere" principle follow karta hai.
Q2. JDK, JRE aur JVM mein difference?
| Term | Full Form | Kaam |
|---|---|---|
| JVM | Java Virtual Machine | Bytecode execute karta hai |
| JRE | Java Runtime Environment | JVM + libraries |
| JDK | Java Development Kit | JRE + development tools (compiler, debugger) |
Q3. Java mein static keyword ka use?
- Static variable: Class-level, sabhi objects share karte hain
- Static method: Object banaye bina call hota hai
- Static block: Class load hote time execute hota hai
Q4. final, finally, finalize mein difference?
final— variable/method/class restrict karta haifinally— exception handling mein hamesha execute hota haifinalize()— GC se pehle call hota hai (Java 9+ deprecated)
Q5. == aur .equals() mein difference?
==— reference compare karta hai.equals()— value/content compare karta hai
java exampleWoHoTech
String s1 = new String("Java");
String s2 = new String("Java");
s1 == s2 // false
s1.equals(s2) // trueQ6. String immutable kyun hai?
- String Pool ka support
- Thread safety
- Security (network/file paths)
- HashCode caching
Q7. StringBuilder vs StringBuffer?
| StringBuilder | StringBuffer | |
|---|---|---|
| -- | -- | -- |
| Thread Safety | No | Yes |
| Speed | Fast | Slow |
Q8. Java pass-by-value hai ya pass-by-reference?
Java sirf pass-by-value use karta hai. Objects ke case mein reference ki copy pass hoti hai.
Q9. Autoboxing aur Unboxing kya hai?
- Autoboxing:
int→Integer(automatic) - Unboxing:
Integer→int(automatic)
Q10. Garbage Collection kya hai?
JVM automatically unused objects ki memory free karta hai. Programmer ko manually free nahi karna padta.
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