why does this does throw a number format exception

Question

its basically a button event that does multiplication

  mul.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent evt) {


                if(Sans == null){
                    temp = text;
                }else {
                    temp = Sans ;
                }
                text = "";

                equal = "mul" ;

                textArea.setText("*");
            }
        });
           this is the action that happens when pressing equal button
                 ans.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent evt) {

                if(equal == "mul"){
                    double a = Double.parseDouble(text);
                    double b = Double.parseDouble(temp);
                    double ans = b*a;
                    String Sans = String.valueOf(ans);
                    textArea.setText(Sans);
                    text = "" ;
                }
                    }

this code gives the result for the first multiplication but gives a numberformatexception on successive multiplication the same code works fine doing a divide operation.

Bug in your code: Do not use `==` to compare strings. `if(equal == "mul")` is wrong; use `if (equal.equals("mul"))` instead. — Jesper, May 23 '13 at 06:54
NFE is thrown when you try to parse something that is not a number. If you'll add the full stacktrace we could help you more. — BobTheBuilder, May 23 '13 at 06:55
Do some debugging. Either use your debugger in the IDE and set a breakpoint on the first Double.parseDouble line, or add some System.out.printlns (I think you're interested in the value of text and temp, then you'll see what is wrong). — Aleksander Blomskøld, May 23 '13 at 06:56
If you added the code related to setting the values of `Sans`. `text`, `temp`, that would help as well. — gkalpak, May 23 '13 at 06:56
these are their initial values String text = "0" ; String temp = "" ; String equal = ""; String Sans = ""; — Ankur Teotia, May 23 '13 at 07:24

score 1 · Answer 1 · edited May 23 '17 at 11:50

1

Update your if condition from

if(equal == "mul")

to

if(equal.equals("mul"))

And learn more about string comparisions. Related post https://stackoverflow.com/questions/767372/java-string-equals-versus

edited May 23 '17 at 11:50

Community

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answered May 23 '13 at 06:56

Juned Ahsan

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@AnkurTeotia print the numbers before you assign them to a double. If a number string is not a valid number for example "7s"/"7x" or anything then you will get numberformatexception while doing Double.parseDouble. So make sure your number string is good to be converted to double. – Juned Ahsan May 23 '13 at 07:19

why does this does throw a number format exception

1 Answers1