ArrayList

I had a doubt concerning ArrayList

If i want to add strings to an ArrayList is it required to have done a
ArrayList prodSku = new ArrayList();

or

will it work fine with

ArrayList prodSku

at the end i want to do

prodSku.add("abc");

Code:

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// This is a declaration.
// The reference "prodSku" is null, ie, does not
// point to or refer to an object.
ArrayList prodSku

// This is a declaration and instantiation.
// Now the reference "prodSku" points to an ArrayList.
ArrayList prodSku = new ArrayList();

// This is okay after "prodSku" has been
// initialized to point/refer to an ArrayList.
// Otherwise this line will generate a
// NullPointerException at compile time.
prodSku.add("abc");

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