Generic JList and ListCellRenderer?

Discussion in 'Java' started by Knute Johnson, Dec 28, 2012.

  1. I've been trying to clean up some really old code and I've hit some
    snags. I've got several modified JLists and the ListCellRenderers for
    them and thought it would make sense to have generic classes that could
    be extended for different data types that need to be displayed. The
    example below displays InetAddresses in the JList. I've got another
    implementation of JList that does a lot more than what this one does but
    I wanted to keep this example simple and focus on the ListCellRenderer.

    MyListCellRenderer extends the getListCellRenderer method of
    DefaultListCellRenderer and adds a new method, textToDisplay(). I added
    a field to the constructor that specifies the class of the data element
    to be displayed. That class information is the test to make the call to
    the textToDisplay() method. The InetAddressListCellRenderer class
    extends MyListCellRenderer to get this to display nice neat Strings for
    the InetAddresses.

    I think this whole thing is a little kludgie. I've been playing with it
    for so long now I'm not getting anywhere anymore. I was hoping somebody
    would say "gee you ought to go this way" or "no that is really brilliant
    code my man!" and I'll leave it as is :).

    Anyway, please take a look and if you have any great ideas, I would
    appreciate the feedback.

    Thanks,

    import java.awt.*;
    import java.io.*;
    import java.net.*;
    import java.util.*;
    import javax.swing.*;
    import javax.swing.border.*;

    public class test6 extends JPanel {
    public test6() throws UnknownHostException {
    Vector<InetAddress> v = new Vector<>();
    v.addElement(InetAddress.getByName("216.240.58.139"));
    v.addElement(InetAddress.getByName("4.2.2.1"));
    v.addElement(InetAddress.getByName("knutejohnson.com"));
    v.addElement(InetAddress.getByName("192.168.3.6"));

    MyJList<InetAddress> list =
    new MyJList<>(new DefaultListModel<InetAddress>());
    list.setCellRenderer(new InetAddressListCellRenderer());
    list.setListData(v);
    add(list);
    }

    public class MyJList<E> extends JList<E> {
    private final DefaultListModel<E> model;

    public MyJList(DefaultListModel<E> lm) {
    super(lm);
    this.model = lm;
    }

    public void setListData(E[] listData) {
    model.clear();
    for (E e : listData)
    model.addElement(e);
    }

    public void setListData(Vector<? extends E> v) {
    model.clear();
    Iterator<? extends E> iter = v.iterator();
    while (iter.hasNext())
    model.addElement(iter.next());
    }
    }

    public class MyListCellRenderer extends DefaultListCellRenderer {
    private final Class clazz;

    public MyListCellRenderer(Class clazz) {
    super();
    setOpaque(true);
    setBorder(new EmptyBorder(1,1,1,1));
    setName("List.cellRenderer");

    this.clazz = clazz;
    }

    public Component getListCellRendererComponent(JList<?> list,
    Object value, int index, boolean isSelected, boolean
    cellHasFocus) {
    setComponentOrientation(list.getComponentOrientation());

    UIDefaults defaults = UIManager.getDefaults();

    Color bg = null;
    Color fg = null;

    JList.DropLocation dropLocation = list.getDropLocation();
    if (dropLocation != null &&
    !dropLocation.isInsert() &&
    dropLocation.getIndex() == index) {
    bg = (Color)defaults.get("List.dropCellBackground");
    fg = (Color)defaults.get("List.dropCellForeground");

    isSelected = true;
    }

    if (isSelected) {
    setBackground(bg == null ?
    list.getSelectionBackground() : bg);
    setForeground(fg == null ?
    list.getSelectionForeground() : fg);
    } else {
    setBackground(list.getBackground());
    setForeground(list.getForeground());
    }

    if (value instanceof Icon) {
    setIcon((Icon)value);
    setText("");
    } else if (clazz.isInstance(value)) {
    setIcon(null);
    // setText(((InetAddress)value).getHostAddress());
    setText(textToDisplay(value));
    /*
    } else {
    setIcon(null);
    setText((value == null) ? "" : value.toString());
    */
    }

    setEnabled(list.isEnabled());
    setFont(list.getFont());

    Border border = null;
    if (cellHasFocus) {
    if (isSelected)
    border = (Border)defaults.get(
    "List.focusSelectedCellHighlightBorder");
    if (border == null)
    border = (Border)defaults.get(
    "List.focusCellHighlightBorder");
    } else
    border = new EmptyBorder(1,1,1,1);
    setBorder(border);

    return this;
    }

    public String textToDisplay(Object value) {
    return value == null ? "" : value.toString();
    }
    }

    public class InetAddressListCellRenderer extends MyListCellRenderer {
    public InetAddressListCellRenderer() {
    super(InetAddress.class);
    }

    public String textToDisplay(Object value) {
    return ((InetAddress)value).getHostAddress();
    }
    }

    public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
    public void run() {
    try {
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    test6 t6 = new test6();
    f.add(t6);
    f.pack();
    f.setVisible(true);
    } catch (Exception e) {
    e.printStackTrace();
    }
    }
    });
    }
    }


    --

    Knute Johnson
    Knute Johnson, Dec 28, 2012
    #1
    1. Advertising

  2. In article <kbkqb6$uu3$>,
    Knute Johnson <> wrote:

    > I've been trying to clean up some really old code and I've hit some
    > snags. I've got several modified JLists and the ListCellRenderers
    > for them and thought it would make sense to have generic classes that
    > could be extended for different data types that need to be displayed.
    > The example below displays InetAddresses in the JList. I've got
    > another implementation of JList that does a lot more than what this
    > one does but I wanted to keep this example simple and focus on the
    > ListCellRenderer.


    Good use of a class literal as runtime type token:

    <http://docs.oracle.com/javase/tutorial/extra/generics/literals.html>

    > MyListCellRenderer extends the getListCellRenderer method of
    > DefaultListCellRenderer and adds a new method, textToDisplay(). I
    > added a field to the constructor that specifies the class of the data
    > element to be displayed. That class information is the test to make
    > the call to the textToDisplay() method. The
    > InetAddressListCellRenderer class extends MyListCellRenderer to get
    > this to display nice neat Strings for the InetAddresses.
    >
    > I think this whole thing is a little kludgie. I've been playing with
    > it for so long now I'm not getting anywhere anymore. I was hoping
    > somebody would say "gee you ought to go this way" or "no that is
    > really brilliant code my man!" and I'll leave it as is :).
    >
    > Anyway, please take a look and if you have any great ideas, I would
    > appreciate the feedback.


    Some suggestions:

    Use the @Override annotation.

    Use the for-each (Iterable) loop in setListData():

    @Override
    public void setListData(Vector<? extends E> v) {
    model.clear();
    for (E e : v) {
    model.addElement(e);
    }
    }

    Consider supporting List:

    public void setListData(List<? extends E> v) {
    model.clear();
    for (E e : v) {
    model.addElement(e);
    }
    }

    Catch the more specific exception:

    catch (UnknownHostException e)

    --
    John B. Matthews
    trashgod at gmail dot com
    <http://sites.google.com/site/drjohnbmatthews>
    John B. Matthews, Dec 29, 2012
    #2
    1. Advertising

  3. On 12/28/2012 5:56 PM, John B. Matthews wrote:
    > In article <kbkqb6$uu3$>,
    > Knute Johnson <> wrote:
    >
    >> I've been trying to clean up some really old code and I've hit some
    >> snags. I've got several modified JLists and the ListCellRenderers
    >> for them and thought it would make sense to have generic classes that
    >> could be extended for different data types that need to be displayed.
    >> The example below displays InetAddresses in the JList. I've got
    >> another implementation of JList that does a lot more than what this
    >> one does but I wanted to keep this example simple and focus on the
    >> ListCellRenderer.

    >
    > Good use of a class literal as runtime type token:
    >
    > <http://docs.oracle.com/javase/tutorial/extra/generics/literals.html>
    >
    >> MyListCellRenderer extends the getListCellRenderer method of
    >> DefaultListCellRenderer and adds a new method, textToDisplay(). I
    >> added a field to the constructor that specifies the class of the data
    >> element to be displayed. That class information is the test to make
    >> the call to the textToDisplay() method. The
    >> InetAddressListCellRenderer class extends MyListCellRenderer to get
    >> this to display nice neat Strings for the InetAddresses.
    >>
    >> I think this whole thing is a little kludgie. I've been playing with
    >> it for so long now I'm not getting anywhere anymore. I was hoping
    >> somebody would say "gee you ought to go this way" or "no that is
    >> really brilliant code my man!" and I'll leave it as is :).
    >>
    >> Anyway, please take a look and if you have any great ideas, I would
    >> appreciate the feedback.

    >
    > Some suggestions:
    >
    > Use the @Override annotation.
    >
    > Use the for-each (Iterable) loop in setListData():
    >
    > @Override
    > public void setListData(Vector<? extends E> v) {
    > model.clear();
    > for (E e : v) {
    > model.addElement(e);
    > }
    > }
    >
    > Consider supporting List:
    >
    > public void setListData(List<? extends E> v) {
    > model.clear();
    > for (E e : v) {
    > model.addElement(e);
    > }
    > }
    >
    > Catch the more specific exception:
    >
    > catch (UnknownHostException e)
    >


    Thanks John.

    --

    Knute Johnson
    Knute Johnson, Dec 30, 2012
    #3
  4. On 12/29/2012 7:11 AM, Chris Uppal wrote:
    > Knute Johnson wrote:
    >
    >> I've been trying to clean up some really old code and I've hit some
    >> snags. I've got several modified JLists and the ListCellRenderers for
    >> them and thought it would make sense to have generic classes that could
    >> be extended for different data types that need to be displayed. The
    >> example below displays InetAddresses in the JList. I've got another
    >> implementation of JList that does a lot more than what this one does but
    >> I wanted to keep this example simple and focus on the ListCellRenderer.

    >
    > Without knowing what directions you intend/expect to extend the code it's a
    > little difficult to make sensible suggestions.
    >
    > So, proceeding with due absence of sense...
    >
    > I don't see what the clazz variable (and the associated instance checks) are
    > buying you. You could try removing them and see if that makes your code come
    > to life. It would certainly remove some of the "kludgy" smell.
    >
    > If that doesn't help, then it may be that you're being bothered by the way that
    > ListCellRenderer has (so to speak) too many responsibilities -- it's
    > simultaneously about /how/ something is displayed and about /what/ is
    > displayed.
    >
    > So (this is only my guess, of course) you're being pulled in two directions: on
    > the one hand your /how/ is pretty much fixed and you want to use nice generic
    > code for it whatever the types of the values, but the /what/ is not generic and
    > will change according to each application. You are being required to do
    > rampant subclassing of something that shouldn't /need/ subclassing.
    >
    > If that sounds as if it might relate to your problem, you could introduce a new
    > kind of object who's only responsibility is to take a value, the element of the
    > List (of type Object -- unless you want to mess with generics), and return a
    > String which is to be the contents of the cell. It might also have a parallel
    > method which takes the (same) List element and returns an Icon (or null).
    >
    > The new object would have appropriate subclasses for InetAddress etc. (which
    > might or might not appear formally as separate classes in your source -- you
    > could instead use anonymous classes to make the getTextFor() and getIconFor()
    > methods "pluggable").
    >
    > So then you have just one subclass of ListCellRenderer which holds an instance
    > of [a subclass of] this new class (instead of the clazz variable), and which
    > always blindly uses that to "fetch" the appropriate String and/or Icon for use
    > for each cell.
    >
    > It's difficult to think of a good name for the new kind of object (and it's
    > subclasses), but in this case I don't think that's the danger sign it normally
    > would be: the reason that it's difficult to find a name is that the obvious
    > names (some variant on "Renderer") are already taken. "TextSupplier" perhaps
    > (or ContentSupplier, or ContentTranslator) ?
    >
    > It could well be that this kind of picture is over-engineered for your purposes
    > (I can't tell). But even if it is, then the real culprit is the Swing
    > architecture which is under-engineered (here), so something may be needed to
    > compensate.
    >
    > -- chris
    >
    >


    Thanks Chris.

    --

    Knute Johnson
    Knute Johnson, Dec 30, 2012
    #4
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