Students of mine are using PMD to check their code for style errors, and are getting a false positive on the SingularField checker when the field is used inside a lambda expression. I’ve found https://sourceforge.net/p/pmd/bugs/1307/ online, which appears to be closed and resolved a year ago, but the code below is still problematic.
I’ve narrowed the problem down to a tiny reproduction. I am using PMD 5.5.1 in class, though I’ve tested the example below with PMD 5.5.2 as well. The code below triggers a SingularField error for timer1, but not for timer2:
/** Dummy class. */
public final class Test {
private Timer timer1;
private Timer timer2;
/** Dummy constructor. */
public Timer() {
this.timer1 = new Timer(0, e -> {
// do nothing for now
});
this.timer2 = new Timer(0, e -> {
// do nothing for now
});
}
/** Use a lambda expression to reference timer1 -- triggers SingularField error. */
private final Runnable play1 = () -> {
this.timer1.start();
};
/** Use an anonymous class to reference timer2 -- no error. */
private final Runnable play2 = new Runnable() {
@Override
public void run() {
this.timer2.start();
}
};
}
It seems that PMD isn’t recognizing the lambda syntax properly. I tried being more explicit and saying Test.this.timer1 to make it really clear that I’m accessing a field, I’ve tried eliminating the this. before timer1, and I’ve tried changing the finality and visibility of the play1 lambda; none of them affected the error.
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