What reasons and situations require overriding the equals and hashCode methods in a class?

Overriding the equals and hashCode methods is necessary when:

• The class represents a logical entity, and object comparison should be based on field values rather than references.
• Objects of this class will be used in hash-based collections (e.g., HashSet, HashMap).

Reasons:

• equals defines when two objects are considered equal.
• hashCode should return the same value for objects that are equal according to equals.

If these methods are not overridden, comparison will be based on references (i.e., objects are equal only if they are the same instance), and the hash code will be based on the object's address, which can lead to incorrect behavior of collections.

Example of overriding:

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

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