The following example is for JSE 1.5. This example uses Quote objects, which are data-centric objects containing information regarding the current price of a stock.

QuoteFilter is an abstract base class (sometimes called an "ABC") which:

• defines isAcceptable, which must be implemented by concrete subclasses (these represent specific filters)
• defines sift, a template method which calls isAcceptable, and which applies a particular filter to a given Collection of Quote objects
• does not have knowledge of any GUI elements

package hirondelle.stocks.table;

import hirondelle.stocks.quotes.Quote;
import java.util.*;

/**
* Allows collections of {@link Quote} objects 
* to be filtered according to a criterion defined by implementors.
* JDK less than 6.
*/
public abstract class QuoteFilter {
  
  /**
  * Defines the criteria by which <tt>aQuote</tt> is accepted or rejected 
  * by this filter.
  */
  abstract public boolean isAcceptable(Quote aQuote);
  
  /**
  * Return a <tt>List</tt> which has the same 
  * iteration order as <tt>aQuotes</tt>, but which includes only those elements 
  * which satisfy {@link #isAcceptable}.
  */
  public final List<Quote> sift(Collection<Quote> aQuotes ){
    /*
    * This is an example of a template method : the general outline is
    * defined here in this abstract base class, but the implementation of 
    * specific steps (in this case the method isAcceptable) is left to 
    * concrete subclasses.
    *
    * Note as well that this method is final, so that no subclass can override this 
    * implementation.
    */
    List<Quote> result = new ArrayList<>();
    for(Quote quote : aQuotes){
      if (isAcceptable(quote)) {
        result.add(quote);
      }
    }
    return result;
  }
}
 

• defines all concrete implementations of QuoteFilter (using static private classes)
• provides a graphical interface for user selection of these filter implementations (using a JTree)

/**
* Graphical component which allows the end user to select a 
* {@link QuoteFilter}, and informs its listeners of changes 
* to this selection.
* JDK less than 6.
*/
public final class QuoteFilterFactory extends JScrollPane implements Observer {

  /**
  * Constructor.
  *  
  * @param aCurrentPortfolio is observed by this class, since the list of 
  * possible filters displayed by this class depends on its content.
  */
  public QuoteFilterFactory (CurrentPortfolio aCurrentPortfolio){
    fCurrentPortfolio = aCurrentPortfolio;
    //bad practice - 'this' is not fully defined until the constructor has returned:
    fCurrentPortfolio.addObserver(this);
    fSelectedFilter = NO_SELECTION_FILTER;
    initGui();
  }
  
  /**
  * Return the <tt>QuoteFilter</tt> 
  * attached to the currently selected item. If no selection is present, 
  * then return a <tt>QuoteFilter</tt> which accepts all {@link Quote} objects.
  */
  public QuoteFilter getSelectedFilter(){
    assert fSelectedFilter != null : "Filter has null value.";
    return fSelectedFilter;
  }
  
  //elided...

  
  // PRIVATE

  private CurrentPortfolio fCurrentPortfolio;
  
  /**
  * The {@link QuoteFilter} corresponding to the user's 
  * current non-null selection.
  */
  private QuoteFilter fSelectedFilter;
  
  /**
  * The {@link QuoteFilter} corresponding to the absence of 
  * any user selection.
  */
  private QuoteFilter NO_SELECTION_FILTER = 
    new QuoteFilterAcceptAll(Consts.EMPTY_STRING)
  ;

  //elided...

  // All QuoteFilter implementations:
  
  /**
  * No {@link Quote} objects are rejected by this filter.
  *
  *<P> Since more than one tree node uses this filter, text is 
  * passed to the constructor to allows for customized display.
  */
  static private class QuoteFilterAcceptAll extends QuoteFilter {
    QuoteFilterAcceptAll(String aText) {
      fText = aText;
    }
    public boolean isAcceptable(Quote aQuote){
      return true;
    }
    @Override public String toString(){
      return fText;
    }
    private final String fText;
  }
  
  /**
  * {@link Quote} objects are accepted only if they are from a specific 
  * {@link Exchange}.
  */
  static private final class QuoteFilterExchange extends QuoteFilter {
    QuoteFilterExchange(Exchange aExchange) {
      fTargetExchange = aExchange;
    }
    @Override public boolean isAcceptable(Quote aQuote){
      return aQuote.getStock().getExchange() == fTargetExchange;
    }
    @Override public String toString(){
      return fTargetExchange.toString();
    }
    private Exchange fTargetExchange;
  }
  
  /**
  * {@link Quote} objects are accepted only if todays price change is 
  * non-negative.
  */
  static private final class QuoteFilterGainers extends QuoteFilter {
    @Override public boolean isAcceptable(Quote aQuote){
      return aQuote.getChange().doubleValue() >= 0.0;
    }
    @Override public String toString(){
      return GAINERS;
    }
  }

  /** 
  * {@link Quote} objects are accepted only if todays price change is negative.
  */
  static private final class QuoteFilterLosers extends QuoteFilter {
    @Override public boolean isAcceptable(Quote aQuote){
      return aQuote.getChange().doubleValue() < 0.0;
    }
    @Override public String toString(){
      return LOSERS;
    }
  }
  
  /** {@link Quote} objects are accepted only if it is an index.  */
  static private final class QuoteFilterIndex extends QuoteFilter {
    @Override public boolean isAcceptable(Quote aQuote){
      return aQuote.getStock().isIndex();
    }
    @Override public String toString(){
      return INDEX;
    }
  }

  /** {@link Quote} objects are accepted only if it is not an index.  */
  static private final class QuoteFilterNonIndex extends QuoteFilter {
    @Override public boolean isAcceptable(Quote aQuote){
      return !aQuote.getStock().isIndex();
    }
    @Override public String toString(){
      return NON_INDEX;
    }
  }
}