How to check that string is not equal to a string then it will work otherwise no? in kotlin

Question

I have a problem to share with you guys a I am trying to check if a string is not equal to nothing and it should be "." value a string if it pass it will do certain line code if not it simply print something but the problem is when i try to put value "." it crashes. So is there any way to fix this?

Here is my kotlin main activity file :

calculate.setOnClickListener {

        if(((distance.text.toString().length >0) &&
                (initalVelocity.text.toString().length>0) &&
                (time.text.toString().length > 0)
                ) && (!((distance.equals(".")) &&
                (initalVelocity.equals(".")) &&
                (time.equals("."))))) {
            val s = distance.text.toString().toDouble()
            val u = initalVelocity.text.toString().toDouble()
            val t = time.text.toString().toDouble()
            val a = (((2* s))-(2*(u*t)))/(t*t)
            answer.setText("answer $a m/(s)^2")
        } else {
            toast("Are u nuts !!!!")
        }

LOG:

 FATAL EXCEPTION: main
Process: com.a3.apurv.physicscalculator, PID: 16094
java.lang.NumberFormatException: For input string: "."
    at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2043)
    at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
    at java.lang.Double.parseDouble(Double.java:539)
    at com.a3.apurv.physicscalculator.AccelerationIVActivity$onCreate$2.onClick(AccelerationIVActivity.kt:31)
    at android.view.View.performClick(View.java:6294)
    at android.view.View$PerformClick.run(View.java:24770)
    at android.os.Handler.handleCallback(Handler.java:790)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6494)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

Possible duplicate of [What is a NumberFormatException and how can I fix it?](https://stackoverflow.com/questions/39849984/what-is-a-numberformatexception-and-how-can-i-fix-it) — Zoe, Jan 01 '18 at 14:45

BakaWaii · Accepted Answer · 2018-01-01T15:28:05.890

1

The problem is in this part of your code:

!((distance.equals(".")) && (initalVelocity.equals(".")) && (time.equals(".")))

It will be true if any of the string doesn't equal to ".". Also, you are comparing the EditText instance instead of the content of it. The condition of your if case should be:

if(distance.text.toString().length > 0 && 
        initalVelocity.text.toString().length > 0 &&
        time.text.toString().length > 0 &&
        !(distance.text.toString().equals(".") || initalVelocity.text.toString().equals(".") || time.text.toString().equals(".")))

Here is an alternative way to approach the same result:

val s = try { distance.text.toString().toDouble() } catch(e: Exception) { null }
val u = try { initalVelocity.text.toString().toDouble() } catch(e: Exception) { null }
val t = try { time.text.toString().toDouble() } catch(e: Exception) { null }
if (s != null && u != null && t != null) {
    val a = (((2* s))-(2*(u*t)))/(t*t)
    answer.setText("answer $a m/(s)^2")
} else {
    toast("Are u nuts !!!!")
}

I use try-catch instead of if-else because calling toDouble of "" and "." will both throw NumberFormatException.

edited Jan 01 '18 at 15:28

answered Jan 01 '18 at 14:31

BakaWaii

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still crashes is there any way ? – a2krocks Jan 01 '18 at 14:33
so How to fix? What should i do now? – a2krocks Jan 01 '18 at 14:36
@ApurvAjayKumarA2K I've edited the condition for checking. It should be comparing the content of the `EditText` instead of the `EditText` itself. – BakaWaii Jan 01 '18 at 14:38
It crashes after updating code i need a better solution – a2krocks Jan 01 '18 at 14:39
Thank you for your help i have fixed it – a2krocks Jan 01 '18 at 14:43
hey is there any When i can do with multiple string to check – a2krocks Jan 01 '18 at 14:56
What do you mean by checking multiple string? – BakaWaii Jan 01 '18 at 15:07
@ApurvAjayKumarA2K I've update the answer for an alternative way to do it. – BakaWaii Jan 01 '18 at 15:28

score 1 · Answer 2 · answered Jan 01 '18 at 14:38

Your code is failing because you're trying to convert the string "." to a number. toDouble (from kotlin-stdlib) will throw a NumberFormatException if the string you're trying to convert is not a valid representation of a number.

The documentation does not specify what the format is so let's dig a little deeper. Judging by the source code, this uses Double#parseDouble(String) internally. This, in turn, uses Double#valueOf(String). If you're treating user input as Double values, have a look at the Javadoc and see what the method does and when. "." might not be the only input you allow that may cause the exception to be thrown. Depending on how complex the cases you need to support in your project are, you may also need to get acquainted with NumberFormat

That said, you need to change your conditional logic to make sure "." (or other non-numeric strings) don't get converted to Double or, alternatively, catch the NumberFormatException after it's thrown and handle it in a user-friendly way.

How to check that string is not equal to a string then it will work otherwise no? in kotlin

2 Answers2