A student is trying to convert the string present in x to a numerical value, so that he can find the square root of the converted value. However the code has an error. Name the error (syntax / logical / runtime). Correct the code so that it compiles and runs correctly.

String x= "25";
int y=Double.parseDouble(x); 
double r=Math.sqrt(y); 
System.out.println(r);

What is the method to check whether a character is a letter or digit?

1. isDigit(char)
2. isLetterOrDigit()
3. isLetterOrDigit(char)
4. isLETTERorDIGIT(char)

Differentiate between boxing and unboxing.