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Java Java Objects (Retired) Creating the MVP Comparing Characters

Posted by Nicholas Steele
Nicholas Steele
683 Points

stuck on java track task? not sure how to compare the last name to a character

I have modeled an assistant for a tech conference. Since there are so many attendees, registration is broken up into two lines. Lines are determined by last name, and they will end up in line 1 or line 2. Please help me fix the getLineFor method.

NEW INFO: chars can be compared using the > and < symbols. For instance 'B' > 'A' and 'R' < 'Z'

ConferenceRegistrationAssistant.java 
public class ConferenceRegistrationAssistant {

  public int getLineFor(String lastName) {
    /* If the last name is between A thru M send them to line 1
       Otherwise send them to line 2 */
    int line = 0;
    if(lastName.substring(0,1) < 'M') {
      int line = 1;
    }
    else {
    int line = 2;
    }
    return line;
  }

}

3 Answers

Andrew Winkler
Andrew Winkler
37,739 Points
Andrew Winkler
Andrew Winkler
37,739 Points

Try this out (I commented to explain the logic):

public class ConferenceRegistrationAssistant {

  public int getLineFor(String lastName) {
    int line = 0;
    if(lastName.charAt(0) > 'M') {
/* The getLineFor method takes a String "lastName" as an argument.
    Strings are concatenations of characters and they can be counted from 0 .
    You can use the charAt() method to compare the char at the place 0 inside String "lastName"
    with a single character of your interest.
    Here we write a condition:  if char at position 0 of the  "lastName" is greater then character 'M',
    the line is 2.
*/

      return line = 2;
// return int 2
    } else
// everething is under 'M'
// line  is 1
    return line = 1;
// return int 1
  }
}

If this is helpful please make sure to vote best answer! Happy coding!

Jeison Dias
Jeison Dias
3,031 Points
Jeison Dias
Jeison Dias
3,031 Points

Really helpful! I wasn't understanding and your logic explanation opened my eyes!

Plamen Neshkov
Plamen Neshkov
18,236 Points
Plamen Neshkov
Plamen Neshkov
18,236 Points

You need to compare the first character of the last name to the aforementioned intervals of characters:

lastName.charAt(0) >= 'A' && lastName.charAt(0) <= 'M'

The reason your code doesn't work is because the substring() method returns a String and not a char primitive type and you cannot compare incompatible types. The Java compiler simply doesn't know how to infer this type of comparison.

Jeff Wilton
Jeff Wilton
16,646 Points
Jeff Wilton
Jeff Wilton
16,646 Points

When you are working on these code challenges, you can hit the preview button to see any compiler messages, such as these in your case:

./ConferenceRegistrationAssistant.java:7: error: bad operand types for binary operator '<'
    if(lastName.substring(0,1) < 'M') {
                               ^
  first type:  String
  second type: char
./ConferenceRegistrationAssistant.java:8: error: variable line is already defined in method getLineFor(String)
      int line = 1;
          ^
./ConferenceRegistrationAssistant.java:11: error: variable line is already defined in method getLineFor(String)
    int line = 2;
        ^
3 errors

The first error is telling you that you can't compare two different types, they must be the same type (either both Strings or both Chars). The substring method returns a string, and 'M' is a char. I would recommend using the charAt method instead of substring since you are only interested in a single char. The other two problems are telling you that you can't create new variables with the same name (int line), so remove the 'int' from the last two.

if(lastName.charAt(0) < 'M') {
      line = 1;
    }
...