[java] UseStringBufferForStringAppends: Wrong example in documentation

[ghost]

Affects PMD Version:

Rule:UseStringBufferForStringAppends

Please provide the rule name and a link to the rule documentation:
https://pmd.github.io/latest/pmd_rules_java_performance.html#usestringbufferforstringappends

Description:
Hi, I have encountered a false negative when PMD tried to detect UseStringBufferForStringAppends. Below is the test case for reproducing this false negative:

Code Sample demonstrating the issue:

public void testUseStringBufferForStringAppends() {
    String a;
    a = "foo";
    a += " bar"; // Should report a warning here
}

Expected outcome:Warning

PMD should report a violation at line 4, but doesn't. This is a false-negative.

Running PMD through: [Maven]

[ghost]

@adangel Hi Andreas, could you please help me check this issue? Thanks!

[adangel]

Hi @Belle-PL ,

the example we have on our documentation is too trivial. Exactly this case has been removed from detection with #1736 . If you create manually a StringBuilder to concatenate two strings, it will be slower - the java compiler optimizes this already for you. See also the comment at #1736.

Btw. the example is of course so trivial, that you would actually just write String a = "foo bar" instead of concatenating constant strings.

We probably should use a more complex example, like

String result = "";
for (int i = 0; i < 10; i++) {
    result += getStringFromSomeWhere(i);
}

This indeed should be written using a StringBuilder.

[ghost]

Thanks for your kind response! Hope this case will be removed soon. I think it is a little misleading.