textfield tx1=new TextField("",35);
textfield tx2=new TextField("",35);
double x1=stringToDouble(tx1.getText());
double x2=stringToDouble(tx2.getText());
textfield tx2=new TextField("",35);
double x1=stringToDouble(tx1.getText());
double x2=stringToDouble(tx2.getText());
textfield tx2=new TextField("",35);
double x1=Double.valueOf(tx1.getText());
double x2=Double.valueOf(tx2.getText());stringToDouble()这方法从哪来的?