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HC Tang
HC Tang

Reputation: 41

String cannot be converted to double error in a function

I am trying to output NaN in string format when x is NaN. However, the console throws up String cannot be converted to double error when I am trying to return string of "NaN" when Double.isNaN is true. I tried parsing string r as a double using Double.parseDouble() but to no avail.

Here is my code:

public static double heaviside(double x) {
    String r = "NaN";
    r = Double.parseDouble(r);
    double result;
    if (Double.isNaN(x)) return r;
    else if (x < 0.0) return result = 0.0;
    else if (x == 0.0) return result = 0.5;
    else return result = 1.0;
}

Console output

ActivationFunction.java:6: error: incompatible types: double cannot be converted to String r = Double.parseDouble(r); ^ ActivationFunction.java:8: error: incompatible types: String cannot be converted to double if (Double.isNaN(x)) return r; ^

Upvotes: 0

Views: 1501

Answers (3)

Amongalen
Amongalen

Reputation: 3131

You problem comes from the fact, that you try to assign double to String variable. r is defines as String and Double.parseDouble(r) returns double. It will work if you assing it to result instead, like so: double result = Double.parseDouble(r);

However, there is no need to parse new double from String in the first place. You want to return NaN when x == NaN. You can just return x in that case because, well, x is NaN. No need for another variable, parsing and all of that.

Upvotes: 3

Pranav P
Pranav P

Reputation: 1815

You are trying to convert String into double and storing its value in r which is a type of String.

You should create another variable of double type and can store that value in that like this: 

public static double heaviside(double x) {
    String r = "NaN";
    double d = Double.parseDouble(r);
    double result;
    if (Double.isNaN(x)) return d;
    else if (x < 0.0) return result = 0.0;
    else if (x == 0.0) return result = 0.5;
    else return result = 1.0;
}

I hope it will help you. Happy coding..!

Upvotes: 1

Eric Guti&#233;rrez
Eric Guti&#233;rrez

Reputation: 145

"NaN" is not a double, you can't convert it to double and not return x because Java returns an exception on line 2 of your code and does not continue to run the rest of the code

Upvotes: 0

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