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.

State the data type and value of res after the following is executed:

char ch = '9';
res= Character.isDigit(ch);