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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.JavaExpression;
import org.checkerframework.framework.qual.SubtypeOf;

/**
 * Indicates that the value assigned to the annotated variable is a key for at least the given
 * map(s).
 *
 * 

The value of the annotation is the reference name of the map. Suppose that {@code config} is a * {@code Map}. Then the declaration * *

{@code   @KeyFor("config") String key = "HOSTNAME"; }
* * indicates that "HOSTNAME" is a key in {@code config}. * *

The value of the annotation can also be a set of reference names of the maps. If {@code * defaultConfig} is also a {@code Map}, then * *

{@code   @KeyFor({"config","defaultConfig"}) String key = "HOSTNAME"; }
* * indicates that "HOSTNAME" is a key in {@code config} and in {@code defaultConfig}. * *

You do not usually need to write {@code @KeyFor} on the key type in a map. That is, you can * declare variable {@code Map myMap;} and the Nullness Checker will apply * {@code @KeyFor} as appropriate. If you redundantly write {@code @KeyFor}, as in {@code * Map<@KeyFor("myMap") String, Integer> myMap;}, then your code is more verbose, and more seriously * the Nullness Checker will issue errors when calling methods such as {@code Map.put}. * * @see EnsuresKeyFor * @see EnsuresKeyForIf * @checker_framework.manual #map-key-checker Map Key Checker */ @Documented @Retention(RetentionPolicy.RUNTIME) @Target({ElementType.TYPE_USE, ElementType.TYPE_PARAMETER}) @SubtypeOf(UnknownKeyFor.class) public @interface KeyFor { /** * Java expression(s) that evaluate to a map for which the annotated type is a key. * * @checker_framework.manual #java-expressions-as-arguments Syntax of Java expressions */ @JavaExpression public String[] value(); }





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