How to clear a JList in Java?

Question

i have a jList in gui where i can add some data with Add button. what i want to add another button called Clear which will clear all elements. i tried this:

private void jButtonClearActionPerfomed(java.awt.event.ActionEvent evt)
{
    DefaultListModel listmodel=new DefaultListModel();
    jList1 = new JList(listmodel);
    if(evt.getSource()==jButtonClear) JList.setListData(new String[0];
    else listmodel.removeAllElements();
}

When I click on Add button this will add elements.

When I click on Clear button this remove elements.

But when I re-click on Add button, there is nothing in the jList1

Faviolafavonian

Answer 1

You should not be reinitializing the entire JList widget just to remove some items from it. Instead you should be manipulating the lists model, since changes to it are 'automatically' synchronized back to the UI. Assuming that you are indeed using the DefaultListModel, this is sufficient to implement your 'Clear All' functionality:

private void jButtonClearActionPerfomed(java.awt.event.ActionEvent evt) {
    if(evt.getSource()==jButtonClear) {
        DefaultListModel listModel = (DefaultListModel) jList1.getModel();
        listModel.removeAllElements();
    }
}

Hawn

Answer 2

There are number of problems, the first been that your example is full of compile problems, so I hope that's not your actual code.

JList does not have static method called setListData. I think you mean jList1 instead.

Each time you click on the clean button, you are creating a new model and component...

private void jButtonClearActionPerfomed(java.awt.event.ActionEvent evt)
{
    // ??
    DefaultListModel listmodel=new DefaultListModel();
    jList1 = new JList(listmodel);
    // ??
    if(evt.getSource()==jButtonClear) jList1.setListData(new String[0]);
    else listmodel.removeAllElements();
}

You've successfully dereferenced what ever jList1 was pointing at, so any time you try and interact with it, you're no longer interacting with the component on the screen.

The other problem is you supplying a empty array to the setListData method, which basically is like saying, "please add nothing to my list"

Try something like this;

private void jButtonClearActionPerfomed(java.awt.event.ActionEvent evt)
{
    DefaultListModel listmodel = (DefaultListModel)jList1.getModel();
    if(evt.getSource()==jButtonClear) {
        listmodel.removeAllElements();
    } else {
        listModel.addElement(new String[]{"Hello"});
    }
}

Quadrature

ok for the copmile errors with your modification, now when i click the Clear button it adds some new datas which i don't know it comes from...But i try this and it clears all data but when i click the Add button it adds new data but it keeps the old data before clearing: code : DefaultListModel listmodel=(DefaultListModel)JList1.getModel(); evt.getSource()==jButtonClear{ listmodel.removeAllElements(); – Faviolafavonian

I've switch the conditions (so that clear now calls removeAll) otherwise it will add a new element. I stole your code and wasn't careful about fixing it. I'm not sure if this is shared code with another action event or not. If not, remove the addElement line – Quadrature

yes it's a shared code with the Add button, i can't put the code here because i'm new here, but here is what is at the end of the code of Add button: jList1.repaint(); jPanelVizualisationOptions1.update(); currentPanel.refresh(); – Faviolafavonian

Answer 3

try this:

DefaultListModel model = new DefaultListModel();
model.clear();
jList1.setModel(model);

Aqualung

Answer 4

try this one:

DefaultListModel listmodel=new DefaultListModel();

JList.setModel(listmodel);

Astarte

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