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Check TextField for null is throwing error

Posted on 2008-06-14
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Last Modified: 2012-05-05
Hey guys,

I was literally inches away from getting this working and I dont know where I've gone wrong...

I have made a simple java panel that is used for pounds and dollar conversion depending on rate. So I have a rate field, pound and dollar fields.
I want java to check for a field being empty, if so throw a JOptionPane alert. I got it to work at one point when the fields were default at 0, it was much easier to check a field for the presence of an integer at the time. What am I doing wrong?


Error: Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: empty String
        at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:994)

float pound, rate, result;
 
pound = Float.parseFloat(jTextField2.getText());
rate = Float.parseFloat(jTextField1.getText());
 
 
if (jTextField1.getText().equals("")){  // If the field is null, request the user to enter a number
 
    JOptionPane.showConfirmDialog((Component)
                null,  "Please enter a value for rate", "alert", JOptionPane.OK_CANCEL_OPTION);
}
else if (jTextField2.getText().equals("")){ // If the field is null, request the user to enter a number
       JOptionPane.showConfirmDialog((Component)
                null,  "Please enter a value for pounds", "alert", JOptionPane.OK_CANCEL_OPTION);
}
else
{
result = pound*rate;
jTextField3.setText(String.valueOf(result));
}
}

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Question by:Arka3L
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4 Comments
 
LVL 23

Expert Comment

by:Ajay-Singh
ID: 21784905
You should first validate the fields before convert it to float
0
 
LVL 23

Accepted Solution

by:
Ajay-Singh earned 2000 total points
ID: 21784908
This should work:
float pound, rate, result;
 
 
if (jTextField1.getText().equals("")){  // If the field is null, request the user to enter a number
 
    JOptionPane.showConfirmDialog((Component)
                null,  "Please enter a value for rate", "alert", JOptionPane.OK_CANCEL_OPTION);
}
else if (jTextField2.getText().equals("")){ // If the field is null, request the user to enter a number
       JOptionPane.showConfirmDialog((Component)
                null,  "Please enter a value for pounds", "alert", JOptionPane.OK_CANCEL_OPTION);
}
else
{
pound = Float.parseFloat(jTextField2.getText());
rate = Float.parseFloat(jTextField1.getText());
 
result = pound*rate;
jTextField3.setText(String.valueOf(result));
}
}
 
 
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0
 
LVL 1

Author Comment

by:Arka3L
ID: 21784943
Wow, I can't believe it was that simple -.-, I will award you the points, but can you explain to me the importance of doing this method? Before I did the check for the field being blank, my floats were above the first if statement and it worked fine. Now that I'm checking the field for being empty I have to add them at the end. I just need to learn a little more before I give the points away otherwise I wont learn :)

Thanks for the help Ajay!
0
 
LVL 23

Expert Comment

by:Ajay-Singh
ID: 21784971
In the code you have, you parse the user input (by calling Float.parseFloat) first.  In the case of bad input its going to throw an exception. The validation can be done alongwith you are parsing the input:
 
float pound, rate, result;
boolean valid = true;
 
try {
   pound = Float.parseFloat(jTextField2.getText());
} catch(ParseFailedException e) {
  // Incorrect input
   valid = false;
   JOptionPane.showConfirmDialog((Component)
                null,  "Please enter a value for pounds", "alert", JOptionPane.OK_CANCEL_OPTION);
}
 
if(valid) {
// parse rate
try {
   rate = Float.parseFloat(jTextField1.getText());
} catch(ParseFailedException e) {
  valid = false;
  // Incorrect input
      JOptionPane.showConfirmDialog((Component)
                null,  "Please enter a value for rate", "alert", JOptionPane.OK_CANCEL_OPTION);
}
}
 
if(valid) {
result = pound*rate;
jTextField3.setText(String.valueOf(result));
}
0

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