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JDT Annotations for Enhanced Null Analysis

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/*******************************************************************************
 * Copyright (c) 2011, 2013 Stephan Herrmann and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     Stephan Herrmann - initial API and implementation
 *     IBM Corporation - bug fixes
 *******************************************************************************/
package org.eclipse.jdt.annotation;

import static java.lang.annotation.ElementType.TYPE_USE;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Qualifier for a reference type in a {@link ElementType#TYPE_USE TYPE_USE} position:
 * The type that has this annotation is intended to not include the value null.
 * 
 * If annotation based null analysis is enabled using this annotation has two consequences:
 * 
 * 
 * Dereferencing an expression of this type is safe, i.e., no NullPointerException can occur at runtime.
 * An attempt to bind a null value to an entity (field, local variable, method parameter or method return value)
 *      of this type is a compile time error.
 * 
 * For the second case, diagnostics issued by the compiler should distinguish three situations:
 * 
 * Nullness of the value can be statically determined, the entity is definitely bound from either of:
 *     the value null, or
 *         an entity with a {@link Nullable @Nullable} type.
 * Nullness cannot definitely be determined, because different code branches yield different results.
 * Nullness cannot be determined, because other program elements are involved for which
 *     null annotations are lacking.
 * 
 * 
 * Note: Since org.eclipse.jdt.annotation 2.0.0, the
 * @Target is {TYPE_USE}. For the old API, see
 * 
 * @NonNull in 1.1.0.
 * 
 * @since 1.0
 */
@Documented
@Retention(RetentionPolicy.CLASS)
@Target({ TYPE_USE })
public @interface NonNull {
	// marker annotation with no members
}