Applying Java in Java

Painting QR Code in Java Applying Java

// Get value for a specific row and column combination public Object getValueAt(int row, int col) { Download download = downloadListget(row); switch (col) { case 0: // URL return downloadgetUrl(); case 1: // Size int size = downloadgetSize(); return (size == -1) "" : IntegertoString(size); case 2: // Progress return new Float(downloadgetProgress()); case 3: // Status return DownloadSTATUSES[downloadgetStatus()]; } return ""; } /* Update is called when a Download notifies its observers of any changes */ public void update(Observable o, Object arg) { int index = downloadListindexOf(o); // Fire table row update notification to table fireTableRowsUpdated(index, index); } }

The DownloadsTableModel class essentially is a utility class utilized by the Downloads JTable instance for managing data in the table When the JTable instance is initialized, it is passed a DownloadsTableModel instance The JTable then proceeds to call several methods on the DownloadsTableModel instance to populate itself The getColumnCount( ) method is called to retrieve the number of columns in the table Similarly, getRowCount( ) is used to retrieve the number of rows in the table The getColumnName( ) method returns a column s name given its ID The getDownload( ) method takes a row ID and returns the associated Download object from the list The rest of the DownloadsTableModel class methods, which are more involved, are detailed in the following sections

The addDownload( ) method, shown here, adds a new Download object to the list of managed downloads and consequently a row to the table:

// Add a new download to the table public void addDownload(Download download) { // Register to be notified when the download changes downloadaddObserver(this); downloadListadd(download); // Fire table row insertion notification to table fireTableRowsInserted(getRowCount() - 1, getRowCount() - 1); }

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This method first registers itself with the new Download as an Observer interested in receiving change notifications Next, the Download is added to the internal list of downloads being managed Finally, a table row insertion event notification is fired to alert the table that a new row has been added

The clearDownload( ) method, shown next, removes a Download from the list of managed downloads:

// Remove a download from the list public void clearDownload(int row) { downloadListremove(row); // Fire table row deletion notification to table fireTableRowsDeleted(row, row); }

After removing the Download from the internal list, a table row deleted event notification is fired to alert the table that a row has been deleted

The getColumnClass( ) method, shown here, returns the class type for the data displayed in the specified column:

// Get a column's class public Class getColumnClass(int col) { return columnClasses[col]; }

All columns are displayed as text (that is, String objects) except for the Progress column, which is displayed as a progress bar (which is an object of type JProgressBar)

The getValueAt( ) method, shown next, is called to get the current value that should be displayed for each of the table s cells:

// Get value for a specific row and column combination public Object getValueAt(int row, int col) { Download download = downloadListget(row); switch (col) { case 0: // URL return downloadgetUrl(); case 1: // Size int size = downloadgetSize(); return (size == -1) "" : IntegertoString(size); case 2: // Progress return new Float(downloadgetProgress()); case 3: // Status

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return DownloadSTATUSES[downloadgetStatus()]; } return ""; }

This method first looks up the Download corresponding to the row specified Next, the column specified is used to determine which one of the Download s property values to return

The update( ) method is shown here It fulfills the Observer interface contract allowing the DownloadsTableModel class to receive notifications from Download objects when they change

/* Update is called when a Download notifies its observers of any changes */ public void update(Observable o, Object arg) { int index = downloadListindexOf(o); // Fire table row update notification to table fireTableRowsUpdated(index, index); }

This method is passed a reference to the Download that has changed, in the form of an Observable object Next, an index to that download is looked up in the list of downloads, and that index is then used to fire a table row update event notification, which alerts the table that the given row has been updated The table will then rerender the row with the given index, reflecting its new values