How do I write a compareTo method which compares objects?

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This is the right way to compare strings:

int studentCompare = this.lastName.compareTo(s.getLastName());

This won’t even compile:

if (this.getLastName() < s.getLastName())

Use
if (this.getLastName().compareTo(s.getLastName()) < 0) instead.

So to compare fist/last name order you need:

int d = getFirstName().compareTo(s.getFirstName());
if (d == 0)
    d = getLastName().compareTo(s.getLastName());
return d;

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