Selgitage, kuidas on seotud Java meetodid equals ja hashCode ning miks nende õige rakendamine on oluline kogumite töös.

In Java, the methods equals and hashCode are closely related and are used for comparing objects and storing them in collections such as HashMap, HashSet.

Rules:

• If two objects are equal according to the equals method (i.e., a.equals(b) == true), they must have the same hashCode.
• If the hashCode of objects differs, equals should return false for them.

Why is this important: Hash-based collections first use hashCode for quick lookup of the bucket, then equals for exact comparison of objects within the bucket. If these methods are not correctly implemented, objects may not be found in the collection, even if they are logically equal.

Example of correct implementation:

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    MyClass myClass = (MyClass) o;
    return field1.equals(myClass.field1) && field2 == myClass.field2;
}

@Override
public int hashCode() {
    return Objects.hash(field1, field2);
}

Proper implementation of equals and hashCode ensures correct functioning of collections and prevents errors during search, addition, and removal of elements.