Affects PMD Version: 6.41.0
Rule: InsufficientStringBufferDeclaration
Description:
When using StringBuilder.setLength(0) to reset the StringBuilder for reuse (to avoid allocating additional instances, especially in loops), PMD assumes that the builder length is 0 if it cannot determine the length from the constructor invocation, and warns about a too-small builder.
There does not seem to be an issue when the constructor uses a hardcoded size, only when the initial constructor size is calculated at runtime and PMD is unable to determine the actual initial size.
Code Sample demonstrating the issue:
public static void foo(int i) {
StringBuilder sb = new StringBuilder(i);
sb.append("ab");
sb.setLength(0); // false positive
sb.append("cd");
}
public static void foo2() {
StringBuilder sb = new StringBuilder(2);
sb.append("ab");
sb.setLength(0); // no problem, no false positive
sb.append("cd");
}
Expected outcome:
PMD reports a violation at line 4, but that's wrong. If PMD cannot determine the initial length from the constructor invocation, it should not assume that the length specified in setLength( ) is the maximum length -- especially when setLength(0) is used, which is basically always a request to reset the builder, not grow it.
Running PMD through: Gradle
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