Document listener brings a null pointer exception

Question

I use a document listener and it brings me a null pointer exception . How could I stop this exception . I use this for search some content of a table. With using this I could search relevant content . Also this brings me a null pointer exception .

These are the steps,

In the beginning,

Vector originalTableModel;
DocumentListener documentListener;

In the counstructor,

originalTableModel = (Vector) ((DefaultTableModel) list_table.getModel()).getDataVector().clone();
//add document listener to jtextfield to search contents as soon as something typed on it
addDocumentListener();

My documentlistener method,

private void addDocumentListener(){
   documentListener = new DocumentListener(){
      public void changedUpdate(DocumentEvent documentEvent){
           search();
      }

      public void insertUpdate(DocumentEvent documentEvent){
           search();
      }

      public void removeUpdate(DocumentEvent documentEvent){
           search();
      }

      private void search(){
           searchTableContents(search_field.getText());
      }

   };
}

My searching Method,

public void searchTableContents(String searchString)
{
    DefaultTableModel currtableModel = (DefaultTableModel) list_table.getModel();
    //To empty the table before search
    currtableModel.setRowCount(0);
    //To search for contents from original table content
    for (Object rows : originalTableModel)
    {
        Vector rowVector = (Vector) rows;
        for (Object column : rowVector)
        {

                if **(column.toString().toLowerCase().contains(searchString.toLowerCase())**)
                {

                    //content found so adding to table
                    currtableModel.addRow(rowVector);
                    break;
                }


        }
    }
}

This is the place where I called this method,

private void search_fieldKeyReleased(java.awt.event.KeyEvent evt)                                                      
{                                                          
    // TODO add your handling code here:
    searchTableContents(search_field.getText());
}

I bold the point where I got this null pointer exception.

Have any ideas ?

Answer 1

Most likely your column variable is null. This will be the case if at least one of the cells in the table is empty. Furthermore, since originalTableModel is taken as a clone of the table model in the constructor, any changes since the clone was taken till the time searchTableContents is run will not be reflected in the originalTableModel.

To fix it, you should change the if to if (column != null && column.toString().toLowerCase().contains(searchString.toLowerCase())).