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Thread: Please help resolve warning re parameterized types / Jlist ListCellRenderer

  1. #1
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    Default Please help resolve warning re parameterized types / Jlist ListCellRenderer

    I'm developing a desktop app using JDK 1.7.0 on a Windows 7 machine, not that that should matter. My question is about parameterized types and specifically a ListCellRenderer for a JList. I have included both an example of the the warnings I am receiving and the code that the compiler is complaining about.

    I admit that I'm still very new to Swing and not all that comfortable with parameterized types beyond simple cases. Any words of wisedom regarding these warnings will be appreciated as will recommendations for a good tutorial on parameterized types.

     

    warning: [unchecked] unchecked call to setCellRenderer(ListCellRenderer<? super E>) as a member of the raw type JList
    scrollingList.setCellRenderer(new MyListCellRenderer());
    where E is a type-variable:
    E extends Object declared in class JList




    class MyListCellRenderer extends JLabel 
                             implements ListCellRenderer<Object> {
     
        public MyListCellRenderer() {
            setOpaque(true);
        }
     
        @Override
        public Component getListCellRendererComponent(JList<?> list,
                                                      Object value,
                                                      int index,
                                                      boolean isSelected,
                                                      boolean cellHasFocus) {
     
            setText(((JLabel)value).getText());
            setIcon(((JLabel)value).getIcon());
     
            Color background;
            Color foreground;
     
            // check if this cell represents the current DnD drop location
            JList.DropLocation dropLocation = list.getDropLocation();
            if (dropLocation != null
            && !dropLocation.isInsert()
            && dropLocation.getIndex() == index) {
                background = Color.PINK.darker();
                foreground = Color.CYAN.brighter();
            }
            else if (isSelected) {
                background = list.getSelectionBackground();
                foreground = list.getSelectionForeground();
            }
            else {
                background = Color.WHITE;  // getBackground is ugly
                foreground = list.getForeground();
            }
     
            setBackground(background);
            setForeground(foreground);
     
            return this;
        }
    }


  2. #2
    Member andbin's Avatar
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    Default Re: Please help resolve warning re parameterized types / Jlist ListCellRenderer

    Quote Originally Posted by mageorge View Post
     

    warning: [unchecked] unchecked call to setCellRenderer(ListCellRenderer<? super E>) as a member of the raw type JList
    scrollingList.setCellRenderer(new MyListCellRenderer());
    where E is a type-variable:
    E extends Object declared in class JList


    To avoid the warning, scrollingList must be:

    JList<Object> scrollingList = new JList<Object>();

    Quote Originally Posted by mageorge View Post
            setText(((JLabel)value).getText());
            setIcon(((JLabel)value).getIcon());
    Speaking in general, it's not very good that the "value" is a JLabel. It should be a simple "bean" class with some properties (in your case for a String and an Icon). Not a GUI component.
    Andrea, www.andbin.net SCJP 5 (91%) SCWCD 5 (94%)

    Useful links for Java beginners My new project Java Examples on Google Code

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