Что не так? Все ж проверяется...
package com.javarush.task.task21.task2104;
import java.util.HashSet;
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(Solution n) {
if (n == null) {
return false;
}
if (n instanceof Solution) {
return true;
}
if (this == n) return true;
if (n.first == null && this.first == null && n.last == null && this.last == null) return true;
if (n.first == null && this.first == null && n.last == this.last) return true;
if (n.first == this.first && n.last == null && this.last == null) return true;
if (n.first == this.first && n.last == this.last) return true;
return true;
}
public int hashCode() {
return 31 * first.hashCode() + last.hashCode();
}
public static void main(String[] args) {
Set<Solution> s = new HashSet<>();
s.add(new Solution("Donald", "Duck"));
System.out.println(s.contains(new Solution("Donald", "Duck")));
}
}