code compiles fine, but the JVM throws a NullPointerException

Question

class Boxing2 {

    static Integer x;

    public static void main(String[] args) {
        doStuff(x);
    }

    static void doStuff(int z) {
        int z2 = 5;
        System.out.println(z2 + z);
    }
}

This code compiles fine, but the JVM throws a NullPointerException

Exception in thread "main" java.lang.NullPointerException at Boxing2.main(Test.java:4)

I cannot figure out the reason of this.

`x` is null, so it can't be **boxed** into an `int` . You can only box things, you cant box nothing ;-) — GhostCat, Jul 20 '18 at 12:34

score 3 · Accepted Answer · edited Jul 20 '18 at 18:27

3

x field is null, so null is passed to doStuff method's x parameter, hence autoboxing null to int type throws NullPointerException.

Integer defaults to null, while int defaults to 0.

edited Jul 20 '18 at 18:27

Roshana Pitigala

7,058
8
38
66

answered Jul 20 '18 at 12:33

Tyvrel

188
1
10

Ah, yes, missed autoboxing in parameter – Tyvrel Jul 20 '18 at 12:35

code compiles fine, but the JVM throws a NullPointerException

1 Answers1