afreechart/src/main/java/org/afree/chart/plot/dial/DialPlot.java
/**
     * Adds a layer to the plot and sends a {@link PlotChangeEvent} to all
     * registered listeners.
     *
     * @param layer  the layer (<code>null</code> not permitted).
     */
Adds a layer to the plot and sends a  PlotChangeEvent to all
registered listeners.

@param layer  the layer (null not permitted).
Adds a layer to the plot and sends a PlotChangeEvent to all registered listeners . @param layer the layer ( null not permitted ) .
public void addLayer(DialLayer layer) {
        if (layer == null) {
            throw new IllegalArgumentException("Null 'layer' argument.");
        }
        this.layers.add(layer);
        layer.addChangeListener(this);
        fireChangeEvent();
    }
public void addLayer ( DialLayer layer ) { if ( layer == null ) { throw new IllegalArgumentException ( "Null 'layer' argument." ) ; } this . layers . add ( layer ) ; layer . addChangeListener ( this ) ; fireChangeEvent ( ) ; }
Adds a layer to the plot and sends a {@link PlotChangeEvent} to all
 registered listeners.
Adds a layer to the plot and sends a { @link PlotChangeEvent } to all registered listeners .