Listing 21-6: A typical way to use SwingWorker

Cristina · February 24th, 2012, 06:08 AM

Dear all,

I have tried to complete the code in Listing 21-6 just to eliminate the compilation errors and get a workable program, even though too simple to illustrate multithreading, as follows:

Code:

import javax.swing.JOptionPane;
import javax.swing.SwingWorker;

import java.util.ArrayList;
import java.util.List;


	class MarketNewsWorker extends SwingWorker <List<String>, String>{
		
		ArrayList<String> someNewsCollection;
		
		MarketNewsWorker(){
			someNewsCollection=new ArrayList<String>();
			someNewsCollection.add("Some");
			someNewsCollection.add("news");
			someNewsCollection.add("collection");
			 }

	     @Override public List<String> doInBackground(){
	         // Make a request to the server and return a result,
	         // i.e. a list of Strings
	    	 
	    	 ArrayList<String> myListOfTextData = new ArrayList<String>();
	    	 
	         for (String news: someNewsCollection){
	              //process each news and report the progress
	        	 myListOfTextData.add(news);
	              publish("Processed the news " + news); //this calls process()
	         }
	        return myListOfTextData;
	    }
	     

	    @Override protected void process(String progressMessage){
	        // display the progress information here
	    	//System.out.println(progressMessage);
	    }

	    @Override protected void done(){
	         // modify UI components here by calling get()
	         // Future's get() gives you the result of
	         // the thread execution
	    	try{
	    	System.out.println(get());
	    	}
	    	catch(Exception e){e.printStackTrace();}
	     }
	   }

	   class TestMarketNews{
	        public static void main(String[] args){
	             new MarketNewsWorker().execute();
	             JOptionPane.showMessageDialog(null, "Bye!");
	        }
	   }

I get an error at the line I underlined in red, saying "The method process(String) of type MarketNewsWorker must override or implement a supertype method" and suggesting to remove the @Override annotation.

I know that here the annotation is not necessary and used just as an example, but still I would like to understand the error message and why I get it only for the method process(), and not for doInBackground() and done(), where I use the same annotation.

jitendrabisht · February 24th, 2012, 08:23 AM

You are getting that error because that method

Code:

protected void process(String progressMessage){
	        // display the progress information here
	    	//System.out.println(progressMessage);
	    }

is not same as in its Super Class
correct method is

Code:

protected void process(List<T> list){
	  
	    }

so you can use this code instead of your code

Code:

protected void process(List<String> progressMessage){
	        // display the progress information here
	    	//System.out.println(progressMessage);
	    }

Hope it'll work better

Cristina · March 15th, 2012, 07:20 AM

Feel so good after completing Lesson 21 assignment

Many thanks for your help!

To populate a Swing view from a file, I found the following link useful:
http://stackoverflow.com/questions/3...ents-of-a-file

Here's my solution:

Code:

public class NewsReaderFrame {
	
	public JTextArea text1;
	public JTextArea text2;
	
	NewsReaderFrame(){
		JPanel textPanel = new JPanel();
		text1 = new JTextArea(30,30);
	    JScrollPane scrollPane1 = new JScrollPane(text1, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
		        JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
	    
	    text2 = new JTextArea(30,50);
	    JScrollPane scrollPane2 = new JScrollPane(text2, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
	        JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
 
		textPanel.add(scrollPane1);
		textPanel.add(scrollPane2);
		
		JPanel buttonPanel = new JPanel();
 		buttonPanel.setLayout(new GridLayout(1,1));
		JButton button = new JButton("Read News");
		button.addActionListener(this.new NewsReaderButtonAction());
		
		buttonPanel.add(button);
		
		JPanel panel = new JPanel();
		panel.setLayout(new BoxLayout(panel,BoxLayout.Y_AXIS));
		
		panel.add(textPanel);
		panel.add(buttonPanel);
		
		JFrame frame = new JFrame("Lesson21: File Reader With SwingWorker");
		
		frame.setContentPane(panel);
		frame.setLocation(100,50);
		frame.setVisible(true);
		frame.pack();
	}
	
	public static void main(String[] args){
				
		NewsReaderFrame nrf = new NewsReaderFrame();
								
	}
	
	class NewsReaderButtonAction implements ActionListener{
		
		public void actionPerformed(ActionEvent e){
			
			System.out.println("Read News: Button Pressed");
			
			File file1 = new File("C:\\Users\\Cristina\\Documents\\raspuns.txt");
			File file2 = new File("C:\\Users\\Cristina\\Documents\\ResearchStatement.tex");
			
			NewsReader nr1 = new NewsReader(file1, text1);
			NewsReader nr2 = new NewsReader(file2, text2);
 
			nr1.execute();
			nr2.execute();

	}
	}	
}