The Java Language:Arrays:Anonymous Arrays

Often it is convenient to create “throwaway” arrays, arrays that are used in one place and never referenced anywhere else. Such arrays don’t need a name because you never need to refer to them again in that context. For example, you may want to create a collection of objects to pass as an argument to some method. It’s easy enough to create a normal, named array, but if you don’t actually work with the array (if you use the array only as a holder for some collection), you shouldn’t need to do this. Java makes it easy to create “anonymous” (i.e., unnamed) arrays. Let’s say you need to call a method named setPets(), which takes an array of Animal objects as arguments. Provided Cat and Dog are subclasses of Animal, here’s how to call setPets() using an anonymous array:

 Dog pokey = new Dog ("gray");  
 Cat boojum = new Cat ("grey");  
 Cat simon = new Cat ("orange");  
 setPets ( new Animal [] { pokey, boojum, simon });  

The syntax looks similar to the initialization of an array in a variable declaration. We implicitly define the size of the array and fill in its elements using the curly-brace notation. However, because this is not a variable declaration, we have to explicitly use the new operator and the array type to create the array object. Anonymous arrays were sometimes used as a substitute for variable-length argument lists to methods, which will be discussed. With the introduction of variablelength argument lists in Java, the usefulness of anonymous arrays has diminished.