Use of Array of length 0? [duplicate]

Question

char[] arrNew = new char[0];
System.out.println(arrNew.length);  // length = 0
arrNew[0]='c'; // ArrayIndexOutOfBoundsException .

In the above code as you can clearly see there is no point in having an array of size 0. As far as I can see there is no practical usage of 0 size array. Can someone explain why the compiler allows creation of 0 length array. And also how is a 0 length array different from an array initialized to null? (i.e, is memory allocated to it as if it were a normal array?). I am sorry if this question seems stupid.

Answer 1

We can return an empty array instead of null from a method, this is called Null object design pattern. Consider the following code

    Person[] res = find(name);
    for(String e : res) {
        System.out.println(e);
    }

if find() does not find anyone it returns an empty array. If find returned null then code would need to treat it as a special case.

We should keep in mind that empty array is immutable so it is logical to use a singleton instead of creating it each time

private static final Person[] NULL = new Person[0];

Person[] find(String name) {
     ...
     if (notFound) {
           return NULL;
     }
     ...