Integration

Some body please guide me about this.

You continue to make it hard for people to 'guide' you when you don't follow their previous advise to first read the documentation or The Java Tutorials to learn how to use Java.

All of your questions can be EASILY answered just by reading the documentation or by reading the appropriate tutorial and trying the examples there.

You have to LEARN how to use Java BEFORE you try to write code that uses it.

This question is a good example.

I am trying to handle square root exception. 

What 'exception' are you talking about? There IS NO EXCEPTION. If you read the Java API for the 'sqrt' function you would see that immediately.

https://docs.oracle.com/javase/7/docs/api/java/lang/Math.html#sqrt(double)

public static double sqrt(double a)
Returns the correctly rounded positive square root of a double value. Special cases:
If the argument is NaN or less than zero, then the result is NaN.
If the argument is positive infinity, then the result is positive infinity.
If the argument is positive zero or negative zero, then the result is the same as the argument.
Otherwise, the result is the double value closest to the true mathematical square root of the argument value.

Parameters:

a - a value.

Returns:

the positive square root of a. If the argument is NaN or less than zero, the result is NaN.

Do you see any 'exception' shown in the above doc API description?

For instance if the argument is positive (i.e. 25) , it displays its result (i.e. 5) in the text area but if the argument is negative it displays "NaN" in the text area instead of "Square root of negative numbers not possible" .

Of course it displays "NaN" - that is EXACTLY what you told it to display:

 double res= Math.sqrt(val);
 taResult.setText(" " + res);

That says do the square root and display the result no matter what that result is. If the result is NaN then display it. If the result is NOT NaN then display it.

So Java did just what you told it.

You did NOT say 'check the result and if it is NaN display some message instead.

}catch(ArithmeticException e){
 taResult.setText("Square root of negative numbers not possible");
 }

Do you see any 'ArithmeticException' listed in the doc API quote I provided above?

Do you see where the doc says that the result can be NaN?

You will continue to have problems with Java, and everything else, until you learn how to use Java.

The easiest way to do that is to use The Java Tutorials and the Java API docs.

Let those docs 'guide' you. Then if you have SPECIFIC questions about what those docs say or about one of the trail examples post your question and ask it.