In your else block add a condition that the count will be incremented only if the given character is a letter or a digit.
if (Character.isLetter(text1.charAt(i)) || Character.isDigit(text1.charAt(i))) {
count++;
}
In your example:
public static int countUniqueCharacters(String text1) {
int count = 0;
for (int i = 0; i < text1.length(); i++) {
if (text1.substring(0, i).contains(text1.charAt(i) + "")) {
System.out.println();
} else if (Character.isLetter(text1.charAt(i)) || Character.isDigit(text1.charAt(i))) {
count++;
}
}
return count;
}