Uninitialized array positions

[manuelmontenegro]

Given the following Java method (can be found in IntegerDivision: 9fe4389 ):

    public int simpleArray(int x) {
        int[] numbers = {x,0};
        return numbers[1];
    }

The javac compiler (openjdk: javac 1.6.0_24) generates the following bytecode:

00:  iconst_2
; Array initialization:
01:  newarray  10
03:  dup
04:  iconst_0
05:  iload_1
06:  iastore
; Return numbers[1]:
07:  astore_2
08:  aload_2
09:  iconst_1
10:  iaload
11:  ireturn

Only the zero-th position of the array is initialized. The first one is not, as JVM's newarray specification specifies the following: Each of the elements of the new array is initialized to the default initial value (§2.3, §2.4) for the element type of the array type.
[Taken from: http://docs.oracle.com/javase/specs/jvms/se7/html/jvms-6.html#jvms-6.5.newarray]

So, there is no need to initialize numbers[1] explicitly in the JVM code. However, Muggl initializes numbers[1] to null. As a consequence, null is returned in a method that should return an int. This generates the following test case, which is ill-typed:

        this.reference0 = null;
                ...
        assertEquals(this.reference0, this.testedClass.simpleArray(this.int1));