Actions

The Command pattern is described in Design Patterns, where menu items are used as an example implementation.

In Swing, the Action interface and the AbstractAction base class implement the Command pattern. They eliminate duplication of code, and separate tasks from the details of their invocation:

Example

A JMenuItem corresponding to File->Save can be created using this Action:


package hirondelle.stocks.file;

import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import hirondelle.stocks.portfolio.PortfolioDAO;
import hirondelle.stocks.portfolio.CurrentPortfolio;
import hirondelle.stocks.util.ui.UiUtil;
import java.util.logging.Logger;
import hirondelle.stocks.util.Util;

/**
* Save the edits performed on the {@link CurrentPortfolio}, and update the display 
* to show that the <tt>CurrentPortfolio</tt> no longer needs a save.
*/
public final class FileSaveAction extends AbstractAction implements Observer {

  /**
  * Constructor.
  *  
  * @param aCurrentPortfolio is to be saved by this action.
  */
  public FileSaveAction(CurrentPortfolio aCurrentPortfolio) {
    super("Save", UiUtil.getImageIcon("/toolbarButtonGraphics/general/Save")); 
    fCurrentPortfolio = aCurrentPortfolio;
    fCurrentPortfolio.addObserver(this);
    putValue(SHORT_DESCRIPTION, "Save edits to the current portfolio");
    putValue(
      ACCELERATOR_KEY, KeyStroke.getKeyStroke(KeyEvent.VK_S, ActionEvent.CTRL_MASK)
    );
    putValue(LONG_DESCRIPTION, "Save edits to the current portfolio");
    putValue(MNEMONIC_KEY, new Integer(KeyEvent.VK_S));    
  }

  @Override public void actionPerformed(ActionEvent e) {
    fLogger.info("Saving edits to the current portfolio.");
    PortfolioDAO portfolioDAO = new PortfolioDAO();
    portfolioDAO.save(fCurrentPortfolio.getPortfolio());
    fCurrentPortfolio.setNeedsSave(false);
    fCurrentPortfolio.notifyObservers();
  }  
  
  /**
  * Synchronize the state of this object with the state of the 
  * <tt>CurrentPortfolio</tt> passed to the constructor.
  *
  * This action is enabled only when the <tt>CurrentPortfolio</tt> is titled and 
  * needs a save.
  */
  @Override public void update(Observable aPublisher, Object aData) {
    setEnabled(fCurrentPortfolio.getNeedsSave() && !fCurrentPortfolio.isUntitled());
  } 
  
  // PRIVATE 
  private CurrentPortfolio fCurrentPortfolio;
  private static final Logger fLogger = Util.getLogger(FileSaveAction.class);
}
 



See Also :
Align menu items
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