org.checkerframework.checker.nullness.qual.Nullable Maven / Gradle / Ivy
package org.checkerframework.checker.nullness.qual;
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;
import org.checkerframework.framework.qual.DefaultFor;
import org.checkerframework.framework.qual.LiteralKind;
import org.checkerframework.framework.qual.QualifierForLiterals;
import org.checkerframework.framework.qual.SubtypeOf;
/**
* {@link Nullable} is a type annotation that makes no commitments about whether the value is {@code
* null}. Equivalently, the type includes the {@code null} value.
*
* The Nullness Checker issues an error if {@code null} is assigned an an expression of {@link
* NonNull} type.
*
*
Programmers typically write {@code @Nullable} to indicate that the value is not known to be
* {@link NonNull}. However, since {@code @Nullable} is a supertype of {@code @NonNull}, an
* expression that never evaluates to {@code null} can have a declared type of {@code @Nullable}.
*
* @see NonNull
* @see MonotonicNonNull
* @see org.checkerframework.checker.nullness.NullnessChecker
* @checker_framework.manual #nullness-checker Nullness Checker
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE_USE, ElementType.TYPE_PARAMETER})
@SubtypeOf({})
@QualifierForLiterals(LiteralKind.NULL)
@DefaultFor(types = Void.class)
public @interface Nullable {}