Basic array initialization and sorting question

Question

this is a rather basic java question

I have an array containing String that i want to sort using java.util.Arrays.sort

when i write

String[] myArray = {"A","B","C"};
java.util.Arrays.sort(myArray);

it gets sorted correctly

however when i have

String[] myArray = new String[10];
myArray[0] = "A";
myArray[1] = "B";
myArray[2] = "C";

java.util.Arrays.sort(myArray);

sort throws a nullreferenceexception

i'm pretty sure its something really dumb i just dont get right now. I have to new the String, because hardcoding default values doesnt get anyone, anywhere.

Answer 1

When you initialize the second array, you only initialize the first three elements. The other elements are initialized to null and thus can't be sorted.

Answer 2

In the source, the method uses compareTo() as a sort condition. Obviously, invoking compareTo() on null, will raise a NullPointerException. As its mentioned in Java Docs that,

All elements in the array must be mutually comparable (that is, e1.compareTo(e2) must not throw a ClassCastException for any elements e1 and e2 in the array)

Of course here its not about ClassCastException, but invocation of comapreTo() is obvious.

[Edited]

P.S. Figuring this out from Exception Stack Trace is your best bet.