why override equals and hashcode in java

1// EXAMPLE CLASS
2public class User {
3    private String name;
4    private int age;
5    private String passport;
6	
7	@Override public boolean equals(Object o) {
8        if (o == this)  {
9          return true;
10        }
11        if (!(o instanceof User)) {
12            return false;
13        }
14
15        User user = (User) o;
16
17        return user.name.equals(name) && 
18				user.age == age && 
19          		user.passport.equals(passport);
20    }
21  
22    @Override public int hashCode() {
23        int result = 17;
24        result = 31 * result + name.hashCode();
25        result = 31 * result + age;
26        result = 31 * result + passport.hashCode();
27        return result;
28    }