org.jetbrains.annotations.Nullable Maven / Gradle / Ivy
/*
* Copyright 2000-2021 JetBrains s.r.o.
*
* 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
*
* https://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 org.jetbrains.annotations;
import java.lang.annotation.*;
/**
* An element annotated with {@link Nullable} claims {@code null} value is perfectly valid
* to return (for methods), pass to (parameters) or hold in (local variables and fields).
* Apart from documentation purposes this annotation is intended to be used by static analysis tools
* to validate against probable runtime errors or element contract violations.
*
* By convention, this annotation applied only when the value should always be checked against {@code null}
* because the developer could do nothing to prevent null from happening.
* Otherwise, too eager {@link Nullable} usage could lead to too many false positives from static analysis tools.
*
* For example, {@link java.util.Map#get(Object key)} should not be annotated {@link Nullable} because
* someone may have put not-null value in the map by this key and is expecting to find this value there ever since.
*
* On the other hand, the {@link java.lang.ref.Reference#get()} should be annotated {@link Nullable} because
* it returns {@code null} if object got collected which can happen at any time completely unexpectedly.
*/
@Documented
@Retention(RetentionPolicy.CLASS)
@Target({ElementType.METHOD, ElementType.FIELD, ElementType.PARAMETER, ElementType.LOCAL_VARIABLE, ElementType.TYPE_USE})
public @interface Nullable {
/**
* @return textual reason when the annotated value could be null, for documentation purposes.
*/
@NonNls String value() default "";
}