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public class Scope {
  public static void main(String[] args) {
    int i = 0;
    for (i = 0; i < 10; i++) {
      // Do operations
    }
  }
}

Reusability is reduced because the value of the loop index, i, is modified by the for statement. Suppose, for example, this code snippet is copied and pasted with the intent to use a different index, j. If the index-variable change were omitted, the new loop would then attempt to iterate over index i. Unexpected behavior can result because i remains in scope.

This code is noncompliant because, even though variable i is not intentionally used outside the for loop, it is declared in method scope. One of the few scenarios where variable i would need to be declared in method scope is when the loop contains a break statement and the value of i must be inspected after conclusion of the loop.

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Minimize the scope of variables where possible, for . For example, by declaring declare loop indices within the for statement:

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This noncompliant code example shows a variable count that is declared outside the counter method, although the variable is not used outside the counter method. The reusability of the method is reduced because the count variable would need to be redefined in the new context.

public class Foo {
  private int count;
  private static final int MAX_COUNT = 10;

  public void counter() {
    count = 0;
    while (condition()) {
      /* ... */
      if (count++ > MAX_COUNT) {
	    return;
      } 
    }
  }

  private boolean condition() {/* ... *}
  // No other method references count 
  // but several other methods reference MAX_COUNT 
}

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public class Foo {
  private static final int MAX_COUNT = 10;

  public void counter() {
    int count = 0;
    while (condition()) {
      /* ... */
      if (count++ > MAX_COUNT) { 
	    return;
      }
    }
  }
  private boolean condition() {/* ... */}
   // No other method references count 
  // but several other methods reference MAX_COUNT 
}

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Detecting multiple for statements that use the same index variable is straightforward; it produces false positives in the unusual case where this behavior is intended by the programmerthe value of the index variable is intended to persist between loops.

Bibliography

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