Interview Revision Notes

A quick, compact revision summary across all modules — ideal for a final review right before an interview.

Fundamentals: JDK = development tools + JRE. JRE = libraries + JVM. JVM runs bytecode. Java is platform-independent because of bytecode + JVM.

Operators & Control Flow: == compares values (or references for objects); .equals() compares object content. switch needs break to avoid fall-through. do-while always runs at least once.

Arrays & Strings: Arrays have a fixed size; array indexing starts at 0. Strings are immutable. StringBuilder is mutable and faster for repeated modifications; StringBuffer is the thread-safe version.

OOP: Four pillars: Encapsulation, Inheritance, Polymorphism, Abstraction. Overloading = same name, different parameters, compile-time. Overriding = same signature in subclass, runtime. Interfaces support multiple inheritance-like behaviour; classes support only single inheritance.

Packages & Exceptions: Checked exceptions are verified at compile-time; unchecked extend RuntimeException. finally always runs. Custom exceptions extend Exception or RuntimeException.

Collections: List allows duplicates and keeps order. Set disallows duplicates. Map stores key-value pairs. HashMap is fast but unordered; TreeMap is sorted; LinkedHashMap preserves insertion order.

Advanced Concepts: Wrapper classes let primitives be used as objects. Generics add compile-time type safety. Lambda expressions implement functional interfaces concisely. Streams process collections declaratively.

Multithreading: Threads allow concurrent execution. synchronized prevents data corruption from simultaneous access. Deadlock happens when threads wait on each other forever. Executor Framework manages thread pools efficiently.

JVM & Memory: Stack stores method calls (per-thread); Heap stores objects (shared). Garbage Collection is automatic and cannot be forced, only requested.

Real-World Practices: Maven manages dependencies and builds. Use .equals(), not ==, for object comparison. Keep methods small, names meaningful, and catch blocks never empty.

Key Points to Remember

• Use this page as your final five-minute review before walking into an interview.
• If any single line here feels unclear, go back to that specific module for a fuller explanation before your interview.
• Confidence in explaining these points out loud, in your own words, matters more than memorizing them word-for-word.