[Code optimization] returns a zero-length array or set.

To get rid of your habit of inheriting from the C language, we have no reason in Java to return NULL for arrays or collections.

private final List<Cheese> InStock =...;public Cheese[] getCheeses() {       if( InStock.size() ==0){            return null;       }}

This is a frequently used return mode, which means that when applying the cheese array, You need to determine whether the array is null.

Cheese[]  cheeses= shop.getCheeses();if(cheeses! =null){   ....}

If we modify the array to be null or the set has no data, a 0 length will be returned, so that it will not be judged during use.

Whether the array and set are empty.

Some people think that the NULL return value is better than the 0-length array because it avoids the overhead required to allocate the array.

This viewpoint is untenable for two reasons. First, it is not advisable to worry about performance issues at this level, because the performance consumption at this level

It is insignificant; second, it is possible to freely share any element object without returning it.

In short, there is no reason to return NULL if the return type is array or set. We use an array or set with a return length of 0.