1Z0-771 case studies
1Z0-771 · Put your knowledge to work in context.
The Oracle Certified Professional: Java SE 21 Developer credential (exam code 1Z0-771) is Oracle's professional-level certification for programmers who build and maintain Java applications on the Java SE 21 platform. It is aimed at developers with real working experience in Java who want formal recognition of advanced language and API skills, and it is commonly sought by backend engineers, enterprise application developers, and anyone whose job involves modernizing code for a long-term-support release. The 1Z0-771 case studies are 5 cases and about 4,171 words.
1Rate-Card Cache: Mutated Keys, a Comparator That Collapses the Map, and a Failing Cleanup Loop
A pricing service caches rate cards in a HashMap<RateKey, RateCard . RateKey is a plain class with a String region and an int tier , with equals and hashCode generated over both fields and a public setTier method.
798 words, about 4 min2Parallel Pipeline That Loses Readings, Collapses Duplicates and Never Logs
A nightly analytics job reads 2.4 million sensor readings and was rewritten with streams for throughput. Version A uses readings.parallelStream().forEach(r - results.add(transform(r))) , where results is a plain ArrayList ; the run reports between 2.31 and 2.40 million results and occasionally throws ArrayIndexOutOfBoundsException from inside ArrayList.add .
812 words, about 4 min3Order Service: Nested Submit Deadlock, a Non-Volatile Flag and a Starved Common Pool
An order service handles requests with new ThreadPoolExecutor(8, 64, 60, SECONDS, new LinkedBlockingQueue< ()) . Each task enriches an order by submitting a second Callable to the same executor and blocking on future.get() with no timeout.
848 words, about 4 min4Modularizing Three Tiers: Split Package, Missing Transitive Requires, and Blocked Reflection
A team is modularizing a three-tier application: com.acme.core (domain types), com.acme.report (reporting API), com.acme.app (entry point). Attempt 1 fails at compile time: core and report both contain package com.acme.util (legacy utility classes copied between teams), and javac reports that the package exists in another module.
859 words, about 4 min5Log Shipper: Descriptor Leak, Symlink Cycle, Bad Relativize, and a Brittle Serialized Config
A log-shipping utility walks /var/log/ingest (about 180,000 files in 4,000 directories) once a minute with Stream<Path s = Files.walk(root); s.filter(p - p.toString().endsWith(".log")).forEach(this::copy); . After three days the JVM dies with 'Too many open files'; a heap dump shows no growth in the application's own collections.
854 words, about 4 min