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Constraint (Guava: Google Core Libraries for Java 11.0.1 API)
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com.google.common.collect
Interface Constraint<E>
@Beta
@GwtCompatible
public interface Constraint<E>
A constraint that an element must satisfy in order to be added to a
collection. For example, Constraints.notNull()
, which prevents a
collection from including any null elements, could be implemented like this:
public Object checkElement(Object element) {
if (element == null) {
throw new NullPointerException();
}
return element;
}
In order to be effective, constraints should be deterministic; that is,
they should not depend on state that can change (such as external state,
random variables, and time) and should only depend on the value of the
passed-in element. A non-deterministic constraint cannot reliably enforce
that all the collection's elements meet the constraint, since the constraint
is only enforced when elements are added.
- Since:
- 3.0
- Author:
- Mike Bostock
- See Also:
Constraints
,MapConstraint
Method Summary | |
---|---|
E |
checkElement(E element)
Throws a suitable RuntimeException if the specified element is
illegal. |
String |
toString()
Returns a brief human readable description of this constraint, such as "Not null" or "Positive number". |
Method Detail |
---|
checkElement
E checkElement(E element)
- Throws a suitable
RuntimeException
if the specified element is illegal. Typically this is either aNullPointerException
, anIllegalArgumentException
, or aClassCastException
, though an application-specific exception class may be used if appropriate.- Parameters:
element
- the element to check- Returns:
- the provided element
toString
String toString()
- Returns a brief human readable description of this constraint, such as
"Not null" or "Positive number".
|
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