[java] [doc] AvoidArrayLoops flags copy assignment in same array as sub-optimal

[linusjf]

Affects PMD Version:
6.25.0

Description:
AvoidArrayLoops flags array copy asignment within loop as sub-optimal. An example can be added how to resolve the violation.

Code Sample demonstrating the issue:

package ds;

public class InsertionSort extends AbstractSort {

  @Override
  protected void sort(long[] a, int length) {
    int in;
    int out;
    resetCounts();

    for (out = 1; out < length; out++) {
      long temp = a[out];
      in = out;
      while (in > 0 && a[in - 1] >= temp) {
        a[in] = a[in - 1];
        --in;
        comparisonCount++;
        copyCount++;
      }
      if (in > 0) comparisonCount++;
      a[in] = temp;
      copyCount++;
    }
  }
}

The optimised loop , no longer flagged by the rule, is as follows:

in = out;
while (in > 0 && a[in - 1] >= temp) {
--in;
++comparisonCount;
++copyCount;
}
System.arraycopy(a, in, a, in + 1, out - in);

Running PMD through: [CLI | Ant | Maven | Gradle | Designer | Other]

[linusjf]

This can be reopened as a documentation issue. An example can be added to this rule.

[linusjf]

It's not obvious from the examples or the documentation that copying of array elements as assignment should be avoided totally.

http://www.javapractices.com/topic/TopicAction.do?Id=3