JList 不会在 javax.swing 中更新

Question

I have a simple code with a JFrame, a JButton, and JList which content is supposed to update once the button is clicked:

private void btnUpdateListActionPerformed(java.awt.event.ActionEvent evt) {    
                                 
    //A default list model containing two strings is created.
    DefaultListModel listModel = new DefaultListModel();
    listModel.addElement("hello");
    listModel.addElement("bye");

    //The JList is updated so that it contains the strings of the default list model.
    list = new JList(listModel);
}  

However, after pressing the button nothing happens; the list remains with its original values:

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How do I resolve this so that the list updates as desired?

Answer 1

Don't create a new JList

//The JList is updated ....
list = new JList(listModel);

This does not "update the JList", but instead creates a new instance, one that is never displayed, and the displayed JList, which now is no longer referred to by the list variable, isn't changed at all.

Instead, set the model of the existing list:

list.setModel(listModel);

The main issue is that you're confusing variable with instance: you need to update the state of the existing instance, not update the variable with an entirely new instance.