SINGLE_TABLE inheritance strategy using enums as discriminator value

I would suggest to invert the relationship: define the discriminator value as a constant in the entity, then wrap it in the enum:

@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(
    name = "FIELD_TYPE",
    discriminatorType = DiscriminatorType.STRING
)
public class Shape {}

@Entity
@DiscriminatorValue(Square.DISCRIMINATOR_VALUE)
public class Square extends Shape {
    public static final String DISCRIMINATOR_VALUE = "SQUARE";
}

@Entity
@DiscriminatorValue(Circle.DISCRIMINATOR_VALUE)
public class Circle extends Shape {
    public static final String DISCRIMINATOR_VALUE = "CIRCLE";
}

@AllArgsConstructor
public enum FieldType {
    SHAPE(Shape.DISCRIMINATOR_VALUE),
    CIRCLE(Circle.DISCRIMINATOR_VALUE);

    @Getter
    private final String discriminatorValue;
}

Apart from eliminating duplication, this code is also less tightly coupled: entity classes don't depend on enum values and can be added without having to change other code; while the enum can "enumerate" different classes from different sources - depending on the context where it is used.