Eclipse marks lines as dead code

Question

I have this function with some dead code, marked by Eclipse.

I have two lines that check a & b. Lines that check b are marked as null.

    public int[] runThis(List<Integer> buildIds, List<Integer> scenarios, boolean oflag) {

    int rating[] = new int[scenarios.size()];

    if(buildIds == null) {
        System.out.println("ERROR - Building ID list is null!");
        return null;
    }

    if(scenarios == null) {
        System.out.println("ERROR - Scenario list is null!"); //dead
        return null; //dead
    }

    return rating;      

}

Why does Ellipse make the two lines as dead? Any help? Thanks very much for your time.

Dissert

Is there any other code in that method? Maybe you've been dereferencing b before, which tells Eclipse that b can't be null at this point. In that case you should also get a warning like "unnecessary null check" at the if (b == null) line. – Ariose

I don't know about Eclipse much but IntelliJ IDEA can analyze your code in real-time and warn you that some code is impossible to reach. In your case, if IntelliJ were to detect that b was never null, then it would warn you that these two lines can never be reached because the condition b == null* is always false. – Lubbi

@Joachim: that particular warning is configureable in Eclipse's settings. I believe it's by default turned off. – Aspia

can you paste the whole method? – Ease

@BalusC: Oh, I didn't remember that. I probably turned it on as soon as I heard about it ;-) pretty useful these ones. – Ariose

Answer 1

Because you've already called scenarios.size() in your array constructor. This guarantees scenarios isn't null or it will have thrown an exception by that point.

Amphibology

Thank you so much for that explanation. I hadn't realized that by evaluating something earlier it's guaranteed NOT to get there because of prior NPE, so hence: "Dead code" warning. – Ulcerate