java - exception handing -

i created program should let user enter loan amount , loan period in number of years text fields, , should display monthly , total payments each interest rate starting 5 percent 8 percent, increments of one-eighth, in text area. may sound stupid not sure how add exception handling add exception handling when non-numeric value entered.for example instead of entering 5 number of years, user enters five.the application should display error message. in advance. package loan;

import javafx.application.application; import javafx.scene.scene; import javafx.stage.stage; import javafx.scene.control.label; import javafx.scene.control.textfield; import javafx.scene.control.textarea; import javafx.scene.control.button; import javafx.scene.control.scrollpane; import javafx.scene.layout.hbox; import javafx.scene.layout.borderpane; import javafx.geometry.pos;  public class loan extends application {     protected textfield tfloanamount = new textfield();     protected textfield tfnumberofyears = new textfield();     protected textarea textarea = new textarea();      @override // override start method in application class     public void start(stage primarystage) {         tfnumberofyears.setprefcolumncount(2);         tfloanamount.setprefcolumncount(7);         textarea.setprefcolumncount(30);          // create button         button btshowtable = new button("show table");          // create hbox         hbox paneforcontrols = new hbox(10);         paneforcontrols.setalignment(pos.center);         paneforcontrols.getchildren().addall(new label("loan amount"), tfloanamount,             new label("number of years"), tfnumberofyears, btshowtable);          // create scrollpane         scrollpane scrollpane = new scrollpane(textarea);          // create pane         borderpane pane = new borderpane();         pane.settop(paneforcontrols);         pane.setcenter(textarea);          // create , register handler         btshowtable.setonaction(e -> {             print();         });          // create scene , place in stage         scene scene = new scene(pane);         primarystage.settitle("loans"); // set stage title         primarystage.setscene(scene); // place scene in stage         primarystage.show(); // display stage     }      private void print() {         // create output string         string output = "";         double monthlyinterestrate; // monthly interest rate         double monthlypayment;  // monthly payment          // add table header         output += "interest rate       monthly payment          total payment\n";          // calculate , add table interest rates output         (double = 5.0; <= 8; += 0.125) {             monthlyinterestrate = / 1200;             monthlypayment = double.parsedouble(tfloanamount.gettext()) *                  monthlyinterestrate / (1 - 1 / math.pow(1 + monthlyinterestrate,                 double.parsedouble(tfnumberofyears.gettext()) * 12));              output += string.format("%-24.3f%-34.2f%-8.2f\n", i,                  monthlypayment, (monthlypayment * 12) *                  double.parsedouble(tfnumberofyears.gettext()));         }          textarea.settext(output);     }         public static void main(string[] args) {             launch(args);      } } 

textfield(tfnumberofyears) [textfield]: https://docs.oracle.com/javase/8/javafx/api/javafx/scene/control/textfield.html, textfield has method public final string gettext(), method returns string.

when use [double.parsedouble(tfnumberofyears.gettext())]: https://docs.oracle.com/javase/7/docs/api/java/lang/double.html

public static double parsedouble(string s) throws numberformatexception

throws:

nullpointerexception - if string null

numberformatexception - if string not contain parsable double.

so can put code inside try/catch block , make desire when user enters 5 instead of 5.

like:

`private void print() {     // create output string     string output = "";     double monthlyinterestrate; // monthly interest rate     double monthlypayment;  // monthly payment      // add table header     output += "interest rate       monthly payment          total payment\n";      // calculate , add table interest rates output     (double = 5.0; <= 8; += 0.125) {         monthlyinterestrate = / 1200;         try{             monthlypayment = double.parsedouble(tfloanamount.gettext()) *              monthlyinterestrate / (1 - 1 / math.pow(1 + monthlyinterestrate,             double.parsedouble(tfnumberofyears.gettext()) * 12));         }         catch(numberformatexception e){             //here write code manage exception          }         try{             output += string.format("%-24.3f%-34.2f%-8.2f\n", i,              monthlypayment, (monthlypayment * 12) *              double.parsedouble(tfnumberofyears.gettext()));         }         catch(numberformatexception e){             //here write code manage exception          }     }      textarea.settext(output); }     public static void main(string[] args) {         launch(args);  }` 

this example of how handle exception.