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Declare all enhanced for statement loop variables to be final. The final declaration causes Java compilers to flag and reject any assignments made to the loop variable.

Noncompliant Code Example

This noncompliant code example attempts to process a collection of objects using an enhanced for loop. It further intends to skip processing one item in the collection.

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Note that if processMe were declared final, a compiler error would result at the attempted assignment.

Compliant Solution

This compliant solution correctly processes the objects in the collection not more than one time.

Collection<ProcessObj> processThese = // ... 

for (final ProcessObj processMe: processThese) {
  if (someCondition) { // found the item to skip
    someCondition = false;
    continue; // skip by continuing to next iteration
  }
  processMe.doTheProcessing(); // process the object
}

Risk Assessment

Assignments to the loop variable of an enhanced for loop (for-each idiom) fail to affect the overall iteration order, lead to programmer confusion, and can leave data in a fragile or inconsistent state.

Automated Detection

This rule is easily enforced with static analysis.

Bibliography

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