# Package org.springframework.lang

package org.springframework.lang
Common annotations with language-level semantics: nullability as well as JDK API indications. These annotations sit at the lowest level of Spring's package dependency arrangement, even lower than `org.springframework.util`, with no Spring-specific concepts implied.

Used descriptively within the framework codebase. Can be validated by build-time tools (for example, FindBugs or Animal Sniffer), alternative JVM languages (for example, Kotlin), as well as IDEs (for example, IntelliJ IDEA or Eclipse with corresponding project setup).

Annotation Interfaces
Class
Description
CheckReturnValue
Specifies that the method return value must be used.
Contract
Specifies some aspects of the method behavior depending on the arguments.
NonNull
A common Spring annotation to declare that annotated elements cannot be `null`.
NonNullApi
A common Spring annotation to declare that parameters and return values are to be considered as non-nullable by default for a given package.
NonNullFields
A common Spring annotation to declare that fields are to be considered as non-nullable by default for a given package.
Nullable
A common Spring annotation to declare that annotated elements can be `null` under certain circumstances.