Core Java: Concept

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ConcurrentHashMap Thread Safety

Modern versions (Java 8+) achieve thread safety using fine-grained synchronization with CAS (Compare-And-Swap) operations and synchronized blocks at the individual bin (bucket) level rather than locking the entire map. It only locks the specific node being modified during a hash collision, allowing concurrent reads and writes with high throughput.

wait() vs sleep() vs join()

• wait(): Defined in Object; pauses thread execution, releases the monitor lock, and waits until notify() or notifyAll() is called. Must be used within a synchronized block.
• sleep(): Defined in Thread (static); pauses execution for a specified duration without releasing locks.
• join(): Defined in Thread; pauses the current thread until the thread it was called on completes execution.

JVM Class Loading Mechanism

Operates through three primary phases adhering to a parent-delegation hierarchy (Bootstrap rightarrow Platform/Extension rightarrow Application ClassLoader):

1. Loading: Reads the .class binary bytecode into memory and creates a Class object.
2. Linking: Verifies bytecode correctness, prepares memory for static variables, and resolves symbolic references.
3. Initialization: Executes static blocks and assigns initial values to static variables.