Why doesn't this if condition work?

Question

I created this code to check whether the text field of calculator has any content. If content is present in the text field, then it should display ".". Otherwise, it should display "0." in the text field. The problem is that the if condition always evaluates to false.

private void dotActionPerformed(ActionEvent evt){
    String dott=display.getText();
    if(dott==null)
    {
        display.setText(display.getText()+"0.");
    }
    else
    {
        display.setText(display.getText()+dot.getText());   
    }
}

An empty text field returns `""`, not `null`. `null` is never returned from `getText`. — Zircon, Jul 08 '16 at 14:23
Exactly. Replace `if (dott == null)` with `if (dott.isEmpty())`, and you're good to go. — Haroldo_OK, Jul 08 '16 at 14:25

score 2 · Answer 1 · edited May 23 '17 at 11:52

2

The string will be "", not null. Use dott.isEmpty() to see if dott has no contents. Here is another post with more details on the difference between .compareTo("") and .isEmpty().

edited May 23 '17 at 11:52

Community

1
1

answered Jul 08 '16 at 14:28

xandermonkey

4,054
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Florent.M · Answer 2 · 2016-07-08T14:26:58.333

1

I think you can do :

if(dott.equals(""))

edited Jul 08 '16 at 14:26

answered Jul 08 '16 at 14:25

Florent.M

74
8

As per @Zircon's comment, I doubt it will ever be null, in this case. – Haroldo_OK Jul 08 '16 at 14:26
3

`dott.isEmpty()` should also work. It's mostly a matter of style. – Haroldo_OK Jul 08 '16 at 14:27

Kaushal28 · Answer 3 · 2016-07-08T14:45:14.693

0

try this String method:

if(dott.isEmpty())
    //your code

or you can also use:

if(dott.compareTo("")==0)
    // your code

edited Jul 08 '16 at 14:45

answered Jul 08 '16 at 14:29

Kaushal28

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score 0 · Answer 4 · answered Jul 08 '16 at 14:34

0

Try something like:

 String dott = ...;
 dott.isEmpty();

or

 dott.equals("");

answered Jul 08 '16 at 14:34

ΦXocę 웃 Пepeúpa ツ

47,427
17
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score 0 · Answer 5 · answered Jul 08 '16 at 14:40

String dott=display.getText();
if(dott==null) // original code; should use isEmpty()
{
    display.setText(display.getText()+"0.");
}

But you already know that display.getText() is empty, so why execute it again? Same for the "else" clause - you already know the value. So you should just write:

String dott=display.getText();
if(dott.isEmpty()) {
    display.setText("0.");
} else {
    display.setText(dott+dot.getText());   
}

Or more concise:

   String dott=display.getText();
   String text = dott.isEmpty() ? "0." : dot.getText();
   display.setText(text);

or even:

   String dott=display.getText();
   display.setText( dott.isEmpty() ? "0." : dot.getText() );

score 0 · Answer 6 · answered Jul 08 '16 at 15:04

0

Replace if(dott==null) by

if(dott.equals(""))

answered Jul 08 '16 at 15:04

Shiv Buyya

3,770
2
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score 0 · Answer 7 · answered Jul 08 '16 at 15:36

You can use StringUtils of apache if you want. Link : https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/StringUtils.html

  private void dotActionPerformed(ActionEvent evt){
        String dott=display.getText();
        if( StringUtils.isEmpty(dott))
        {
            display.setText(display.getText()+"0.");
        }
        else
        {
            display.setText(display.getText()+dot.getText());   
        }
    }

Why doesn't this if condition work?

7 Answers7