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)

Give the output of the following code:

String P = "20", Q ="19";
int a = Integer.parseInt(P);
int b = Integer.valueOf(Q);
System.out.println(a+""+b);