How can I use custom objects in HashSet and TreeSet?

How can I use custom objects in HashSet and TreeSet?

To use custom objects in HashSet and TreeSet, you need to override the equals() and hashCode() methods for HashSet, and the compareTo() method for TreeSet.

Can you show me an example of a custom object?

Sure! Here's a simple example:

class Person {
    String name;
    int age;

    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Person)) return false;
        Person person = (Person) o;
        return age == person.age && name.equals(person.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }
}

How do I add this custom object to a HashSet?

You can add it like this:

HashSet<Person> people = new HashSet<>();
people.add(new Person("Alice", 30));
people.add(new Person("Bob", 25));

What about using it in a TreeSet?

For TreeSet, your custom object should implement Comparable. Here's how:

class Person implements Comparable<Person> {
    // ... existing code ...

    @Override
    public int compareTo(Person other) {
        return this.age - other.age; // Compare by age
    }
}

TreeSet<Person> sortedPeople = new TreeSet<>();
sortedPeople.add(new Person("Alice", 30));
sortedPeople.add(new Person("Bob", 25));