warningThresholdField.addFocusListener(this);
    thresholdPanel.add(warningThresholdField);
    assertionPanel.add(thresholdPanel);
    //file panel
    filePanel = new FilePanel(JMeterUtils.getResString("file_visualizer_output_file"), ".txt");
    filePanel.addChangeListener(this);
    assertionPanel.add(filePanel);
    mainPanel.add(assertionPanel, BorderLayout.NORTH);
    add(mainPanel, BorderLayout.CENTER);