清除 Java 中的列表

Question

I have 2 jlist and 2 jbuttons. The Ok button grabs the selected items and adds them to a list. Then the redo button, renables the Ok button and clears the lists. The error refers to the clear button, while clearing the lists. The system prints the lists at Ok button. Then when Clear is clicked, Ok is enabled but error comes up.

Here is the code:

public class bcquery extends JPanel implements ActionListener {

    public List<String> feedlist = new ArrayList<String>();
    public List<String> prodlist = new ArrayList<String>();

public bcquery() {

final JButton button1 = new JButton("OK");
        button1.setEnabled(false);

        final JButton button2 = new JButton("CLEAR");

String[] feedStrings = { "a", "b", "c"};
        String[] prodStrings = { "d", "e", "f", "g"}


final JList feedList = new JList(feedStrings);
        feedList.setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);

final JList prodList = new JList(prodStrings);
        prodList.setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);


button1.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent e)
            {
                String feedstr = feedList.getSelectedValuesList().toString();

                feedlist = Arrays.asList(feedstr);

                String prodstr = prodList.getSelectedValuesList().toString();
                prodlist = Arrays.asList(prodstr);

                System.out.println(feedlist);
                System.out.println(prodlist);

                button1.setEnabled(false);
            }
        });      

        button2.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent e)
            {

                feedlist.clear();
                prodlist.clear();
                button1.setEnabled(true);
                 System.out.println(feedlist);
                 System.out.println(prodlist);
            }
        }); 


private static void createAndShowGUI() {
            //Create and set up the window.

            JFrame frame = new JFrame("Test");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setSize(400, 400);
            JFrame.setDefaultLookAndFeelDecorated(true);

            frame.add(new bcquery());
            frame.setResizable(false);


            frame.pack();
            frame.setVisible(true);
        }

        public static void main(String[] args) {
            //Schedule a job for the event dispatch thread:
            //creating and showing this application's GUI.
            SwingUtilities.invokeLater(new Runnable() {
                public void run() {
            //Turn off metal's use of bold fonts
                UIManager.put("swing.boldMetal", Boolean.TRUE);


            createAndShowGUI();
                }
            });

    }
        @Override
        public void actionPerformed(ActionEvent arg0) {
            // TODO Auto-generated method stub

        }
}

Error:

Exception in thread "AWT-EventQueue-0" java.lang.UnsupportedOperationException
    at java.util.AbstractList.remove(Unknown Source)
    at java.util.AbstractList$Itr.remove(Unknown Source)
    at java.util.AbstractList.removeRange(Unknown Source)
    at java.util.AbstractList.clear(Unknown Source)
    at biocore.bcquery$4.actionPerformed(bcquery.java:175)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$200(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

Arrays#asList() returns a fixed-size list backed by the specified array -- any call to set will work, but remove() and other methods will throw an UnsupportedOperationException . To create a modifiable one, use a list constructor that takes a collection as argument, such as new ArrayList() .

So, change your code to:

feedlist = new ArrayList<String>(Arrays.asList(feedstr));

and:

prodlist = new ArrayList<String>(Arrays.asList(prodstr));