DCL30-J. Do not attempt to assign to the loop variable in an enhanced for loop

The enhanced for statement introduced in Java 1.5, commonly referred to as the for-each idiom, is primarily used for iterating over collections of objects. While similar to the for statement, this idiom cannot be used to assign values to the loop variable.

Noncompliant Code Example

This noncompliant example attempts to initialize a Character array using an enhanced for loop. However, because the loop variable cannot be assigned to, the array is not suitably initialized.

Character[] array = new Character[10];
for(Character c: array) 
  c = 'x'; // initialization attempt

for(int i=0;i<array.length;i++) 
  System.out.print(array[i]);  // prints 10 "null"s

Compliant Solution

This compliant solution correctly initializes the array using a for loop.

Character[] array = new Character[10];
for(int i=0;i<array.length;i++) 
  array[i] = 'x';

for(int i=0;i<array.length;i++) 
  System.out.print(array[i]);  // prints 10 "x"s

Risk Assessment

Attempts to assign to the loop variable from within the enhanced for loop (for-each idiom) are futile and may leave the class in a fragile, inconsistent state.

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Other Languages

TODO

References

[[JLS 05]] Section 14.14.2 "The enhanced for statement"

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