Use zero-length arrays instead of null

zhenge10

If a method returns an array which can be empty, do not allow it to
return null. Instead, return a zero-length array.
This simplifies the client, since they never have to check for null
values.
Example
import java.util.*;
public class StockPortfolio {
  //..elided
  /**
  * A field is implemented internally as a Collection,
  * but offered to the user of this class as an Array.
  * This array is never null, even if the underlying Collection is
  * empty.
  */
  public String[] getStocks() {
    /*
    NO_STOCKS plays a double role here. If there are elements in fStocks, then
    toArray will allocate a new array, using NO_STOCKS simply as an indicator
    of the proper type to use. If fStocks has no elements at all, then toArray
    will simply return the NO_STOCKS array itself.
    */
    return (String[]) fStocks.toArray(NO_STOCKS);
  }
  // PRIVATE //
  /** The underlying collection.  */
  private List fStocks;
  /** A constant, empty array, to be used instead of a null array.  */
  private static final String[]  NO_STOCKS = new String[0];
}
Another alternative is to use a collection instead of an array, if possible.
The
Collections
class contains these constants, which you may find useful :

• 
  Collections.EMPTY_LIST
• 
  Collections.EMPTY_SET
• 
  Collections.EMPTY_MAP
  

               
               
               

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