Собственно я тут и застрял. Есть же проверка? Тесты все проходит.
package com.javarush.task.task21.task2104;
import java.util.HashSet;
import java.util.Objects;
import java.util.Set;
/*
Equals and HashCode
*/
public class Solution {
private final String first, last;
public Solution(String first, String last) {
this.first = first;
this.last = last;
}
public boolean equals(Object n) {
if(!(n instanceof Solution)) return false;
if(n==this) return true;
if(n.getClass() == getClass()) {return true;}
Solution solution = (Solution) n;
if(solution.first==null&&first==null&& solution.last!=null&&last!=null)
return solution.last.equals(last);
if(solution.last==null&&last==null&& solution.first!=null&&first!=null)
return solution.first.equals(first);
if(solution.last==null&&last==null&&solution.first==null&&first==null){
return true;}
return solution.first.equals(first)&&solution.last.equals(last);
}
@Override
public int hashCode() {
int result = 0;
if(first==null || last==null) return result;
result = 31*(first.hashCode()+last.hashCode());
return result;
}
public static void main(String[] args) {
Set<Solution> s = new HashSet<>();
s.add(new Solution("Donald", "Duck"));
s.add(new Solution(null, "Duck"));
s.add(new Solution("Donald", null));
s.add(new Solution(null, null));
System.out.println(s.contains(new Solution("Donald", "Duck")));
System.out.println(s.contains(new Solution(null, "Duck")));
System.out.println(s.contains(new Solution("Donald", null)));
System.out.println(s.contains(new Solution(null, null)));
}
}