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Concurrency (`synchronized`, `volatile`, locks), `CompletableFuture`, JVM memory model basics, records/sealed types, advanced Streams, and common performance pitfalls. Mix of single-answer and multiple-answer items.
Interfaces and abstract classes, generics, collections/`HashMap`, exceptions and try-with-resources, `Optional`, Streams basics, and equals/hashCode contracts. Mix of single-answer and multiple-answer items.
Java foundations: primitives vs references, classes and methods, String immutability, arrays/lists, control flow, and the JVM entry point. Mix of single-answer and multiple-answer items.
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