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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.MonotonicQualifier;
import org.checkerframework.framework.qual.SubtypeOf;
/**
* Indicates that once the field (or variable) becomes non-null, it never becomes null again. There
* is no guarantee that the field ever becomes non-null, but if it does, it will stay non-null.
*
* Example use cases include lazy initialization and framework-based initialization in a
* lifecycle method other than the constructor.
*
*
A monotonically non-null field has these two properties:
*
*
* - The field may be assigned only non-null values.
*
- The field may be re-assigned as often as desired.
*
*
* When the field is first read within a method, the field cannot be assumed to be non-null.
* After a check that a {@code MonotonicNonNull} field holds a non-null value, all subsequent
* accesses within that method can be assumed to be non-null, even after arbitrary external
* method calls that might access the field.
*
*
{@code MonotonicNonNull} gives stronger guarantees than {@link Nullable}. After a check that a
* {@link Nullable} field holds a non-null value, only accesses until the next non-{@link
* org.checkerframework.dataflow.qual.SideEffectFree} method is called can be assumed to be
* non-null.
*
*
To indicate that a {@code MonotonicNonNull} or {@code Nullable} field is non-null whenever a
* particular method is called, use {@link RequiresNonNull}.
*
*
Final fields are treated as MonotonicNonNull by default.
*
*
This annotation is associated with the {@link
* org.checkerframework.checker.nullness.NullnessChecker}.
*
* @see EnsuresNonNull
* @see RequiresNonNull
* @see MonotonicQualifier
* @see org.checkerframework.checker.nullness.NullnessChecker
* @checker_framework.manual #nullness-checker Nullness Checker
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE_USE)
@SubtypeOf(Nullable.class)
@MonotonicQualifier(NonNull.class)
public @interface MonotonicNonNull {}