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Understand Java Collections Framework and Stream API
Learn multithreading, synchronization, and concurrent collections
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Object-oriented programming principles
Java Collections Framework (List, Set, Map)
Multithreading and concurrency
Stream API and functional programming
Exception handling and best practices
JVM internals and garbage collection
A: ArrayList uses dynamic array, fast random access O(1), slow insertion/deletion in middle O(n). LinkedList uses doubly-linked nodes, slow random access O(n), fast insertion/deletion O(1). Use ArrayList for frequent access, LinkedList for frequent insertions/deletions. ArrayList is generally preferred unless you have specific LinkedList use case.
A: == compares references (memory addresses) for objects, values for primitives. .equals() compares object content (must override for custom classes). For Strings: == checks if same object, .equals() checks if same characters. Always use .equals() for String comparison. Override equals() and hashCode() together.
A: GC automatically reclaims memory from unreachable objects. Types: Serial GC (single-threaded), Parallel GC (multiple threads), CMS (concurrent mark-sweep, low pause), G1 GC (region-based, default in Java 9+), ZGC (ultra-low pause). Choice depends on heap size, pause time requirements, throughput needs.
A: Streams process sequences of elements with functional operations. Collections store data, Streams process data. Streams are lazy (terminal operation triggers execution), can be parallel, consumed once. Example: list.stream().filter().map().collect(). Use for data transformation pipelines. Don't modify source during stream operations.
Master multithreading: synchronized, volatile, Lock, Executors, CompletableFuture
Understand JVM memory model: heap, stack, metaspace, garbage collection
Know design patterns commonly used in Java: Singleton, Factory, Builder, Observer
Practice with Java 8+ features: lambdas, streams, Optional, method references
Understand exception hierarchy and checked vs unchecked exceptions
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