Add Fork/Join design pattern (#3227)

[SandhyaDevadiga]

Fixes #3227

What this PR does

Implements the Fork/Join concurrency pattern using a parallel array
summation example.

Files added

• SumTask.java — RecursiveTask that splits the array and sums in parallel
• ForkJoinSumCalculator.java — Wrapper class that manages the ForkJoinPool
• App.java — Demo showing parallel sum of 10 million numbers
• SumTaskTest.java — 6 unit tests for the recursive task
• ForkJoinSumCalculatorTest.java — 5 unit tests for the calculator
• README.md — Pattern explanation with examples and diagrams
• pom.xml — Maven module configuration

[github-actions]

PR Summary

Implements the Fork/Join concurrency pattern using a parallel array summation example. Adds a standalone module fork-join with App, SumTask, ForkJoinSumCalculator, and unit tests, plus documentation.

Changes

File	Summary
fork-join/README.md	Added README explaining the Fork/Join pattern with a Java example that sums a large array, including concepts, usage, and sample output.
fork-join/pom.xml	Introduced fork-join module pom with dependencies and build setup for tests and demo.
fork-join/src/main/java/com/iluwatar/forkjoin/App.java	Demo app that constructs a 10 million element array and computes its sum via ForkJoinSumCalculator, outputting results and timing.
fork-join/src/main/java/com/iluwatar/forkjoin/ForkJoinSumCalculator.java	Wrapper around ForkJoinPool to calculate sums; supports default common pool and custom parallelism; guards against null/empty input.
fork-join/src/main/java/com/iluwatar/forkjoin/SumTask.java	RecursiveTask that divides work by halving the range; uses a threshold for direct sum; validates start/end and combines left/right results.
fork-join/src/test/java/com/iluwatar/forkjoin/ForkJoinSumCalculatorTest.java	Unit tests for ForkJoinSumCalculator including null/empty arrays and large inputs; tests custom parallelism.
fork-join/src/test/java/com/iluwatar/forkjoin/SumTaskTest.java	Unit tests for SumTask covering small/large ranges, partial ranges, empty ranges, single element, million elements, and invalid start>end.
pom.xml	Updated parent pom to include the new fork-join module in the build.

---

autogenerated by presubmit.ai

[github-actions]

🚨 Pull request needs attention.

Review Summary

Commits Considered (1)

• 0f14977: Add fork-join pattern implementation

Files Processed (7)

• fork-join/README.md (1 hunk)
• fork-join/pom.xml (1 hunk)
• fork-join/src/main/java/com/iluwatar/forkjoin/App.java (1 hunk)
• fork-join/src/main/java/com/iluwatar/forkjoin/ForkJoinSumCalculator.java (1 hunk)
• fork-join/src/main/java/com/iluwatar/forkjoin/SumTask.java (1 hunk)
• fork-join/src/test/java/com/iluwatar/forkjoin/ForkJoinSumCalculatorTest.java (1 hunk)
• fork-join/src/test/java/com/iluwatar/forkjoin/SumTaskTest.java (1 hunk)

Actionable Comments (1)

• fork-join/src/main/java/com/iluwatar/forkjoin/SumTask.java [50-55]

  possible bug: "Guard against invalid index range in SumTask"

Skipped Comments (2)

• fork-join/src/main/java/com/iluwatar/forkjoin/App.java [28-28]

  performance: "High memory usage in demo due to full array materialization"

• fork-join/pom.xml [41-41]

  maintainability: "Main class configuration in assembly plugin"

[codecov]

Codecov Report

❌ Patch coverage is 72.09302% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.57%. Comparing base (74d2dbe) to head (f96697f).
⚠️ Report is 18 commits behind head on master.

Files with missing lines	Patch %	Lines
...-join/src/main/java/com/iluwatar/forkjoin/App.java	0.00%	12 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3550      +/-   ##
============================================
+ Coverage     83.24%   83.57%   +0.33%     
- Complexity     4025     4225     +200     
============================================
  Files          1060     1110      +50     
  Lines         14246    14950     +704     
  Branches        686      708      +22     
============================================
+ Hits          11859    12495     +636     
- Misses         2100     2162      +62     
- Partials        287      293       +6     

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[github-actions]

✅ LGTM!

Review Summary

Commits Considered (1)

• f5fe108: Add input validation for start > end in SumTask

Signed-off-by: SandhyaDevadiga sandhyadevadiga8197@gmail.com

Files Processed (2)

• fork-join/src/main/java/com/iluwatar/forkjoin/SumTask.java (1 hunk)
• fork-join/src/test/java/com/iluwatar/forkjoin/SumTaskTest.java (1 hunk)

Actionable Comments (0)

Skipped Comments (1)

• fork-join/src/main/java/com/iluwatar/forkjoin/SumTask.java [37-44]

  possible bug: "Guard against end exceeding array length."

[iluwatar]

You need to add the new module to the parent pom.xml, otherwise CI does not build it

[github-actions]

✅ LGTM!

Review Summary

Commits Considered (1)

• 0a403c3: Add fork-join module to parent pom.xml

Files Processed (1)

• pom.xml (1 hunk)

Actionable Comments (0)

Skipped Comments (1)

• pom.xml [141-141]

  maintainability: "Introduce a new module to the Maven reactor"

[github-actions]

🚨 Pull request needs attention.

Review Summary

Commits Considered (1)

• 4a9ef8f: Add missing assertThrows import in SumTaskTest

Files Processed (1)

• fork-join/src/test/java/com/iluwatar/forkjoin/SumTaskTest.java (1 hunk)

Actionable Comments (1)

• fork-join/src/test/java/com/iluwatar/forkjoin/SumTaskTest.java [81-85]

  possible issue: "Constructor validation for invalid ranges"

Skipped Comments (6)

• fork-join/src/test/java/com/iluwatar/forkjoin/SumTaskTest.java [13-22]

  readability: "Clarify end-exclusive semantics in tests"

• fork-join/src/test/java/com/iluwatar/forkjoin/SumTaskTest.java [25-35]

  test: "Boundary test for threshold"

• fork-join/src/test/java/com/iluwatar/forkjoin/SumTaskTest.java [39-46]

  readability: "End index semantics in documentation"

• fork-join/src/test/java/com/iluwatar/forkjoin/SumTaskTest.java [50-57]

  maintainability: "Explicit empty-range validation"

• fork-join/src/test/java/com/iluwatar/forkjoin/SumTaskTest.java [60-67]

  testing: "Single-element range behavior"

• fork-join/src/test/java/com/iluwatar/forkjoin/SumTaskTest.java [70-78]

  performance: "Performance considerations for large input"

[github-actions]

✅ LGTM!

Review Summary

Commits Considered (1)

• f96697f: Format fork-join code with Spotless

Files Processed (4)

• fork-join/src/main/java/com/iluwatar/forkjoin/App.java (1 hunk)
• fork-join/src/main/java/com/iluwatar/forkjoin/ForkJoinSumCalculator.java (1 hunk)
• fork-join/src/main/java/com/iluwatar/forkjoin/SumTask.java (1 hunk)
• fork-join/src/test/java/com/iluwatar/forkjoin/SumTaskTest.java (1 hunk)

Actionable Comments (0)

Skipped Comments (1)

• fork-join/src/main/java/com/iluwatar/forkjoin/SumTask.java [34-42]

  maintainability: "Guard against null input in SumTask constructor."