Unable to compare empty Strings

Question

can you check why this code jumps to else with the conditions like e1="1", e2="2", e3=""

if (e1=="" || e2=="" || e3==""){
                Context context = getApplicationContext();
                CharSequence text = "Fill in all required fields!";
                int duration = Toast.LENGTH_SHORT;
                Toast toast = Toast.makeText(context, text, duration);
                toast.setGravity(Gravity.CENTER|Gravity.CENTER, 0, 0);
                toast.show();
            }
            else {
                m=Integer.parseInt(e1);
                std=Integer.parseInt(e2);
                nhv=Integer.parseInt(e3);
            rsl=((std*std)*((t1+t2)*(t1+t2)))/((m-nhv)*(m-nhv));
            if (Math.round(rsl) < rsl) {
                rsl = Math.round(rsl) +1; 
            } 
            else {
                rsl=Math.round(rsl);
            }
            et4.setText(""+rsl);
        }

@iamnotmaynard: This is a little different since it is Android — Engineer2021, Mar 04 '14 at 18:30
@GIJoe ,not sure if serious or just joking ,its Java, it doesn't matter where you run it. — SteveL, Mar 04 '14 at 19:32
@SteveL: https://en.wikipedia.org/wiki/Comparison_of_Java_and_Android_API — Engineer2021, Mar 04 '14 at 19:34
@GIJoe I just read that entry. It says nothing about `Strings`, and there's no reason to believe it's any different from regular Java in that regard. Indeed, judging by your own answer, the behavior is the same. Thus, Android or not, I'd say this is a duplicate. — Reinstate Monica -- notmaynard, Mar 04 '14 at 19:43
@GIJoe ,Seems that you are correct about the differences, dalvik doesn't use Java SE library but a "clone" of it, but it still uses a pool for the strings ,so in this case there is no difference at all at how you compare the Strings — SteveL, Mar 04 '14 at 19:45
@SteveL: There is a difference.. can't use .isEmpty for instance... there are better ways than just comparing it per the link above — Engineer2021, Mar 04 '14 at 19:46
@GIJoe What can't use `isEmpty()`? It's a standard part of the `String` class. — Reinstate Monica -- notmaynard, Mar 04 '14 at 19:48
@GIJoe I mean it's a standard part of Java (I suppose since 1.6). Don't know about Android; your own answer uses that method (I see you state "available in Android 2.3", though you could be more clear that it is not available before that). It is also not necessary, as skiwi's answer gives (IMO) the best, most versatile, Java-vs.-Android–agnostic solution: comparing in a `null`-safe way against the empty string using `equals()`. In any case, OP's code is failing precisely for the reason given in the linked question, hence marked as duplicate. — Reinstate Monica -- notmaynard, Mar 04 '14 at 19:58

score 2 · Accepted Answer · answered Mar 04 '14 at 18:25

2

For String comparison you need to use .equals(), like e1.equals(""), or argubly better "".equals(e1).
The second form is argubly better as it can never throw a NullPointerException.

Keep in mind that only primitives int, etc. should be compared with ==, everything else should be compared with Object#equals(Object).

answered Mar 04 '14 at 18:25

skiwi

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actually, the right way is to use `isEmpty`, if using Android 2.3 or greater or `TextUtils` – Engineer2021 Mar 04 '14 at 18:26
+1 I'd say your second form is _inarguably_ better, as it is inherently null-safe. – Reinstate Monica -- notmaynard Mar 04 '14 at 20:22
@iamnotmaynard: both of my examples are null safe. TextUtils.isEmpty checks for null. You can look at the code yourself in Android. – Engineer2021 Mar 04 '14 at 20:34

VipulKumar · Answer 2 · 2014-03-04T20:30:53.887

1

Simply use:

if (e1.isEmpty() || e2.isEmpty() || e3.isEmpty())

edited Mar 04 '14 at 20:30

answered Mar 04 '14 at 18:46

VipulKumar

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score 0 · Answer 3 · answered Mar 04 '14 at 18:26

Since you are checking if your String is null or empty, use the method designed for it:

if (myString != null && !myString.isEmpty()) 
{ 

// doSomething

}

Anything else is prone to bugs or just isn't clear.

Note: This is available in Android 2.3.

Google also provides this via TextUtils:

if (TextUtils.isEmpty(value))
{
    // do something
}

Internally TextUtils.isEmpty() checks if the length of the String is 0 (and does a null check).

Unable to compare empty Strings

3 Answers3