Cardinality (enum) API Cardinality.java enum Cardinality { ZERO (1) ONE (2) MULTIPLE (3) boolean isZero() boolean isOne() boolean isMultiple() } 1 ZERO The container is empty. 2 ONE The container has exactly one element. 3 MULTIPLE The container has at least two elements. Members ZERO The container is empty. ONE The container has exactly one element. MULTIPLE The container has at least two elements.