| /* |
| * Copyright (C) 2007 The Guava Authors |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package com.google.common.collect; |
| |
| import com.google.common.annotations.GwtCompatible; |
| |
| /** |
| * A constraint that an element must satisfy in order to be added to a |
| * collection. For example, {@link Constraints#notNull()}, which prevents a |
| * collection from including any null elements, could be implemented like this: |
| * <pre> {@code |
| * |
| * public Object checkElement(Object element) { |
| * if (element == null) { |
| * throw new NullPointerException(); |
| * } |
| * return element; |
| * }}</pre> |
| * |
| * <p>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. |
| * |
| * @author Mike Bostock |
| */ |
| @GwtCompatible |
| interface Constraint<E> { |
| /** |
| * Throws a suitable {@code RuntimeException} if the specified element is |
| * illegal. Typically this is either a {@link NullPointerException}, an |
| * {@link IllegalArgumentException}, or a {@link ClassCastException}, though |
| * an application-specific exception class may be used if appropriate. |
| * |
| * @param element the element to check |
| * @return the provided element |
| */ |
| E checkElement(E element); |
| |
| /** |
| * Returns a brief human readable description of this constraint, such as |
| * "Not null" or "Positive number". |
| */ |
| @Override |
| String toString(); |
| } |