Calculator square root event listener

Question

I am trying to write a calculator using JButtons added onto Jpanels. Getting numbers to add , divide, multilpy etc. is simple enough, but i need to write an event handler for a button which calculates the square root of a given number. This is easy enough if you want the square root of 4,9,16,25 etc but if you enter a number which produces a decimal point value it doesn't work.
I am trying to do this using a variable "number" which is of type double, but have tried using it as a float, but it still doesn't work! here is my code for handling a click on the Square root JButton.
     if(e.getActionCommand().equals("Sqrt")){
     number = new Double(jtf.getText().trim()).doubleValue();
     double rootNum = 1.000;
     while(rootNum*rootNum <= number){
          double rootTester = rootNum * rootNum;
          if(rootTester == number){
               jtf.setText(String.valueOf(rootNum));
rootNum = rootNum+1;

Answer 1

How about
double answer = Math.sqrt(number);