Odd TableModel Null Pointer

Question

I am getting an odd null pointer. This is my TableModel:

private class Model extends AbstractTableModel implements IEventRespondedToListener{

    private List<ModelPojo> elements;

    private String[] columnNames = new String[]{
        "Class",
        "Event",
        "Event Id",
        "Time"
    };

    public void Model(){
        elements = new ArrayList<>();
    }

    @Override
    public int getRowCount() {
        return elements.size();
    }
    ...

It is created like so:

public UpdateWindow(UpdateManager updateManager){
        this.updateManager = updateManager;
        model = new Model();

However, the exception I get is a null pointer:

java.lang.NullPointerException
    at com.dvsd.profmetric.jms.UpdateWindow$Model.getRowCount(UpdateWindow.java:60)
    at javax.swing.JTable.getRowCount(JTable.java:2664)
    at javax.swing.plaf.basic.BasicTableUI.createTableSize(BasicTableUI.java:1692)
    at javax.swing.plaf.basic.BasicTableUI.getPreferredSize(BasicTableUI.java:1733)
    at javax.swing.JComponent.getPreferredSize(JComponent.java:1659)
    at javax.swing.ScrollPaneLayout.preferredLayoutSize(ScrollPaneLayout.java:495)
    at java.awt.Container.preferredSize(Container.java:1794)

Which points to this line:

return elements.size();

I dont understand how this can be null if elements is created inside the constructor. Any ideas?

Answer 1

This

public void Model(){

should probably be

public Model(){

The addition of void makes it a void method and not a constructor. So when you use public Model(), you call the implicit default constructor (assuming there is no other constructor) where elements is not given a value and therefore remains null.