Java Practice Questions

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Software Engineering & Backend

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Java Hard

Software Engineering & Backend → Java

What is the Module System (JPMS) introduced in Java 9 and what problem does it solve compared to the classpath?

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Java Hard

Software Engineering & Backend → Java

What is the consequence of calling `parallel()` on a stream with a stateful intermediate operation like `sorted()`?

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Java Hard

Software Engineering & Backend → Java

What is `Cleaner` API in Java 9+ and how does it improve over `finalize()`?

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Java Hard

Software Engineering & Backend → Java

What is the difference between `Stream.generate()` and `Stream.iterate()` for creating infinite streams?

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Java Hard

Software Engineering & Backend → Java

What is the purpose of `@SafeVarargs` annotation in Java?

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Java Hard

Software Engineering & Backend → Java

What is the behavior of `TreeMap` when using a `Comparator` inconsistent with `equals()`?

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Java Hard

Software Engineering & Backend → Java

What is the JVM’s safepoint and why does Stop-the-World GC require all threads to reach one?

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Java Hard

Software Engineering & Backend → Java

What is the difference between `Collectors.toUnmodifiableList()` and `Collections.unmodifiableList(Collectors.toList())`?

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Java Hard

Software Engineering & Backend → Java

What is `sealed` interface combined with `non-sealed` permitted subtype in Java 17+?

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Java Hard

Software Engineering & Backend → Java

What is `ForkJoinPool.commonPool()` and when should it be avoided?

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Java Hard

Software Engineering & Backend → Java

What does `CompletableFuture.allOf()` return and what is required to collect results?

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Java Hard

Software Engineering & Backend → Java

What is the difference between `String.chars()`, `String.codePoints()`, and how do they differ for supplementary characters?

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Java Hard

Software Engineering & Backend → Java

What is the problem with double-checked locking for singletons before Java 5, and how did Java 5 fix it?

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Java Hard

Software Engineering & Backend → Java

What is `record` pattern matching in Java 21 and what does it enable?

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Java Hard

Software Engineering & Backend → Java

What is the difference between `WeakHashMap` and a regular `HashMap` with `WeakReference` values?

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Java Hard

Software Engineering & Backend → Java

What is the output of the following code? “`java var list = List.of(3, 1, 4, 1, 5); list.stream() .distinct() .sorted() .limit(3) .forEach(System.out::print); “`

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Java Hard

Software Engineering & Backend → Java

What is `Project Loom`’s virtual thread and how does it differ from a platform thread?

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Java Hard

Software Engineering & Backend → Java

What is `ClassLoader` delegation model and what is the parent-first loading order?

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