How to make a Scanner accept only alphabetical character using If statement - string

Question

I am very much a beginner at Java programming I'm in the middle of writing a program that sorts names in alphabetical order. How can I code an "if" statement so that it only accepts alphabetical characters? In my code I have "if (in.hasNext() != String)" which is clearly wrong, but im just trying anything now. Here is my code.
import java.util.*;
public class AlphaOrder
{
public static void main(String[] args)
{
ArrayList<String> names = new ArrayList<String>();
System.out.println("Enter a name, enter \"Sort\" to sort the names alphabetically, enter \"Quit\" to end: ");
Scanner in = new Scanner(System.in);
while (in.hasNext())
{
names.add(in.next());
if (in.hasNext("Sort"))
{
System.out.println("The names in alphabetical order are: " + names);
}
if (in.hasNext("Quit"))
{
System.out.println("This Program has stopped.");
}
if (in.hasNext() != String)
{
System.out.println("Please enter only alphabetical characters.");
}
}
}
}

Answer 1

1) You probably want to change your logic a bit:
import java.util.*;
public class AlphaOrder
{
public static void main(String[] args) {
ArrayList<String> names = new ArrayList<String>();
System.out.println("Enter a name, enter \"Sort\" to sort the names alphabetically, enter \"Quit\" to end: ");
Scanner in = new Scanner(System.in);
while (in.hasNext()) {
String sLine = in.next ();
if (sLine.equals ("Sort")) {
System.out.println("The names in alphabetical order are: " + names);
doSort ();
}
if (sLine.equals ("Sort")) {
System.out.println("This Program has stopped.");
doExit ();
}
if (!isAlpha (sLine)) {
System.out.println("Please enter only alphabetical characters.");
continue;
}
names.add(sLine);
}
}
}
2) There are lots of ways to check "isAlpha()". I would look at "regular expressions":
http://www.vogella.com/articles/JavaRegularExpressions/article.html
3) Here's one "naive" implementation:
boolean isAlpha (String s)
{
String s2 = s.toUpperCase();
for (int i = 0; i < s2.length(); i ++) {
if (s2.charAt(i) < 'A' || s2.charAt(i) > 'Z')
return false;
}
return true;
}