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

Implemented the Fork/Join concurrency pattern to sum a large array in parallel. Introduced a dedicated module fork-join containing App demo, ForkJoinSumCalculator wrapper, and SumTask RecursiveTask. Added unit tests for SumTask and ForkJoinSumCalculator, plus README documenting the pattern with examples and diagrams. Included Maven module (pom.xml) to package and run the demo.

Changes

File	Summary
fork-join/README.md	Explains the Fork/Join pattern with a Java example that sums a long array. Includes design rationale, a RecursiveTask-based SumTask, a ForkJoinSumCalculator wrapper, and an App demo. Also contains tests harness and a Maven module configuration.
fork-join/pom.xml	Provides Maven module setup for the Fork-Join pattern project, including test dependency and mainClass for the assembled artifact.
fork-join/src/main/java/com/iluwatar/forkjoin/App.java	Demo app that constructs 10M numbers, uses ForkJoinSumCalculator to compute their sum in parallel, and prints result, expected value, correctness, timing, and processor count.
fork-join/src/main/java/com/iluwatar/forkjoin/ForkJoinSumCalculator.java	Wrapper around ForkJoinPool to execute a SumTask over an array; supports default common pool and custom parallelism; validates input.
fork-join/src/main/java/com/iluwatar/forkjoin/SumTask.java	Recursive task that sums a long array, splitting by halves until the threshold; includes input validation for start vs end; uses fork/join for parallel computation.
fork-join/src/test/java/com/iluwatar/forkjoin/ForkJoinSumCalculatorTest.java	JUnit tests for the calculator: zero for null/empty arrays, correct sums for small/large arrays, and custom parallelism.
fork-join/src/test/java/com/iluwatar/forkjoin/SumTaskTest.java	Tests for SumTask: direct sums for small arrays, large sums via fork/join, partial ranges, edge cases, million-element case, and exception when start > end.

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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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.31%. Comparing base (74d2dbe) to head (f5fe108).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3550      +/-   ##
============================================
+ Coverage     83.24%   83.31%   +0.07%     
  Complexity     4025     4025              
============================================
  Files          1060     1060              
  Lines         14246    14246              
  Branches        686      686              
============================================
+ Hits          11859    11869      +10     
+ Misses         2100     2091       -9     
+ Partials        287      286       -1     

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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."