How to solve the error { java.lang.NumberFormatException: empty String }

Question

Sir,
I am using the following code and get subjected error.
{error}{
java.lang.NumberFormatException: empty String
     at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1011)
     at java.lang.Double.parseDouble(Double.java:540)
     at invoice.InvoiceController$4.changed(InvoiceController.java:192)
}{error}
and
//wt ,  sValExlSt1 and sPrice1 are numbers
wt1.textProperty().addListener(new ChangeListener<String>() {
                public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
                    sValExlSt1.setText(String.valueOf(
                            Double.parseDouble(newValue)  * Double.parseDouble(sPrice1.getText())));
        } catch (NumberFormatException e1) {
}Please help.

Answer 1

One way is to check each input variable for valid numbers and if a blank or a text is detected, then make that variable zero.
wt1.textProperty().addListener(new ChangeListener<String>() {
                public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
                    final double doubleTXTValue = 0.0;
                    final double doubleNewValue = 0.0;
                    try {doubleTXTValue = Double.parseDouble(sPrice1.getText());} catch(Exception e) {}
                    try {doubleNewValue = Double.parseDouble(newValue);} catch(Exception e) {}
                    sValExlSt1.setText(String.valueOf(
                            doubleNewValue  * doubleTXTValue));
            });The above code will make sure the user does not enter invalid double values of any type.
You can take this further by inserting the old value of the variables or presenting an error to the user.
If only blank values need to be checked then you can use a more simplistic check by just checking for blanks.
wt1.textProperty().addListener(new ChangeListener<String>() {
                public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
                    final double doubleTXTValue = 0.0;
                    final double doubleNewValue = 0.0;
                    if (sPrice1.getText().trim().length() > 0) doubleTXTValue = Double.parseDouble(sPrice1.getText());
                    if (newValue.trim().length() > 0) doubleNewValue = Double.parseDouble(newValue);
                    sValExlSt1.setText(String.valueOf(
                            doubleNewValue  * doubleTXTValue));
            });