Question

I had a serious bug in my code, which luckily I found :), because I forgot to change the method’s return type signature (from int to Integer) and my app was crashing without any warning.

I had the following method:

public static int getDataSourceIdForName(String name) {
    Integer i = dsNameToIdMap.get(name);
    return i;
}

It was crashing my app. I observed that it was crashing only when a special case occurred and the name was actually not in the map (Map<String, Integer> dsNameToIdMap = new HashMap<>()) thus it was returning null. I would expect a running application to throw a NullPointerException but this was not the case and the app was simply dying and I had a trip full of excitement to find the bug 🙂

Since I would like to have my IDE’s support in avoiding those situations in future, I am asking you guys how to set NetBeans to warn of those situations, i.e. when I am returning an object in a function which return signature is a primitive type, as I cannot figure it out myself.

UPDATE:
I have found the real problem. The code is in fact throwing the NullPointerException, as Jon rightly argued 🙂 It was only my clients ‘survival mechanism’ that was hiding it, as you can see in the sample below:

public class WhyNoNullPointerException {
    private static int test() {
        Integer i = null;
        return i;
    }

    public static void main(String[] args) throws InterruptedException {
        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {

                for (int i = 0; i < 100; i++) {
                    System.out.println("i = " + i);
                    if (i == 10) {
                        try{
                           test();
                        }finally{
                            run();
                        }
                    }
                }
            }
        });
        t.setDaemon(true);
        t.start();
        Thread.sleep(1111);
    }
}

Since the program in finally tries to stay alive by restarting its main operational loop, for this reason it ‘hides’ the NullPointerException.

To avoid this situation in future I will now always, in this self restarting code, add a catch for Exception before the finally block as a good practice this way an exception will not be ‘lost’ (I had the block in the first place in my code I had a byte reading there which can throw IOException).

As to development of a hint I found a very nice tutorial over which I will go today and hopefully will have a working hint (link below). Thanks for your links guys (@JonSkeet and @Nambari) they were very useful in finding some more about the hint development.

NetBeans Java Hint Module Tutorial.

Answer 1

It really does throw NullPointerException:

import java.util.*;

public class Test {
    private static final Map<String, Integer> map
        = new HashMap<String, Integer>();

    public static void main(String[] args) {
        getInt("Foo");
    }

    public static int getInt(String name) {
        Integer i = map.get(name);
        return i;
    }
}

Result:

c:\Users\Jon\Test>java Test
Exception in thread "main" java.lang.NullPointerException
        at Test.getInt(Test.java:13)
        at Test.main(Test.java:8)

Now you may or may not also want NetBeans to warn on auto-unboxing… but it’s worth at least checking what’s going on first 🙂

I found a plugin which highlights auto-boxing/unboxing and varargs, but it’s very old and may well not be supported on the version you’re using.

I’d expect this to be configurable as a compiler option (it is in Eclipse) but I don’t have enough experience with NetBeans to say much more.