private void addPoint(){
    	double ansd = 0;
		String ans = null;
		ans =  (String)JOptionPane.showInputDialog(this, "New point", "Add New Point", JOptionPane.PLAIN_MESSAGE, null, null, "");		
		if ((ans != null) && (ans.length() > 0)) {
        	ansd = (Double.valueOf(ans)).doubleValue();
        	try{
        		if (ansd <= obj_sel.maxC && ansd >= obj_sel.minC){	 
        			ContinuousAttributeDomain dom = obj_sel.domain.getContinuous();
        			dom.addKnot(ansd, 0.0);
        		}
	        	else{
	        		JOptionPane.showMessageDialog(this, "Out of range", "Error", JOptionPane.WARNING_MESSAGE);      
	            	addPoint();
	        	}	
        	}catch(NumberFormatException e){                    
        		JOptionPane.showMessageDialog(this, "Invalid Entry", "Error", JOptionPane.WARNING_MESSAGE);      
        		addPoint();
        	}
		}
    }