What methods or properties need to be changed in an object to use it as a key in HashMap?

To use an object as a key in a HashMap, it is necessary to override the equals() and hashCode() methods.

• hashCode() should return an integer value that corresponds to the hash code of the object. Objects that are equal according to equals() should have the same hashCode().
• equals() should correctly compare objects for equality based on your class's logic.

Example:

public class Person {
    private String name;
    private int age;

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

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

Without the correct implementation of these methods, HashMap may not work correctly, for example, it may not find keys or may create duplicates.