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