abstract compareTo method not being overrided

Question

When compiling the code below, I get the following error:

PersonalInformation is not abstract and does not override abstract method compareTo(Object) in Comparable

I assume that means I have a problem with my compareTo method. But everything seems to be all right. Anyone have a suggestion?

import java.util.*;
public class PersonalInformation implements Comparable
{
private String givenName;
private String middleInitial;
private String surname;
private String gender;
private String emailAddress;
private String nationalId;
private String telephoneNum;
private String birthday;

public PersonalInformation(String gN, String mI, 
        String sur, String gen, String eMa, String natId,
        String teleNum, String birthd)

{
        givenName = gN;
        middleInitial = mI;
        surname = sur;
        gender = gen;
        emailAddress = eMa;
        nationalId = natId;
        telephoneNum = teleNum;
        birthday = birthd;


}


public int compareTo(PersonalInformation pi)
{
 return (this.gender).compareTo(pi.gender);
}

}

Answer 1

Do this:

public int compareTo(Object pi) {
    return ((PersonalInformation )(this.gender)).compareTo(((PersonalInformation ) pi).gender);
}

or better

public class PersonalInformation implements Comparable<PersonalInformation>

If you implement the Comparable Interface you have to implement it either for all Objects using the first method or type your class the second way.

Answer 2

You need to implement Comparable<PersonalInformation> rather than Comparable for your class to compile and work.

If you are implementing Comparable, the expected method signature is compareTo(Object o) which is missing in your class and hence the error.

Answer 3

See juergen d's answer, much better.

You're overloading the method:

public int compareTo(PersonalInformation pi)
{
    return (this.gender).compareTo(pi.gender);
}

instead of overriding it:

public int compareTo(Object pi)

It could be something like:

public int compareTo(Object pi)
{
    if ( ! pi instanceof PersonalInformation )
        return false;
    return (this.gender).compareTo( (PersonalInformation)pi.gender );
}