Use zero-length arrays instead of null

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 class contains these constants, which you may find useful :

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