Why does java allow NPE

Question

How come javac doesn't emit error on this code?

private static int compute(int v) {
    return v == 0 ? null : v;
}

Surely, compute(0) will throw NullPointerException . I would expect the java compiler to prevent this by doing some basic static code analysis, just like it would prevent

private static int compute(int v) {
    if (v == 0)
        return null;
    else
        return v;
}

Answer 1

Why does java allow NPE?

To indicate an exceptional condition (and allow the programmer to potentially recover ).

In your example, Java allows both autoboxing and unboxing . The null boxes the int to an Integer (which is then unboxed to an int ).