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The Checker Framework enhances Java’s type system to make it more powerful and useful. This lets software developers detect and prevent errors in their Java programs. The Checker Framework includes compiler plug-ins ("checkers") that find bugs or verify their absence. It also permits you to write your own compiler plug-ins.

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package org.checkerframework.checker.lock.qual;

import java.lang.annotation.*;

import org.checkerframework.framework.qual.SubtypeOf;
import org.checkerframework.framework.qual.TargetLocations;
import org.checkerframework.framework.qual.TypeUseLocation;

/**
 * If a variable {@code x} has type {@code @GuardSatisfied}, then all
 * lock expressions for {@code x}'s value are held.
 * 
 *
 * Written on a formal parameter (including the receiver), this annotation
 * indicates that the {@literal @}{@link GuardedBy} type for
 * the corresponding actual argument at the method call site
 * is unknown at the method definition site, but any lock expressions
 * that guard it are known to be held prior to the method call.
 * 

 *
 * For example, the formal parameter of the String copy constructor,
 * {@link String#String(String s)}, is annotated with {@code @GuardSatisfied}.
 * This requires that all locks guarding the actual argument are held when
 * the constructor is called.  However, the definition of the constructor
 * does not need to know what those locks are (and it cannot know, because
 * the constructor can be called by arbitrary code).
 * 
 *
 * @see GuardedBy
 * @see Holding
 * @checker_framework.manual #lock-checker Lock Checker
 * @checker_framework.manual #lock-checker-polymorphism-example Lock Checker polymorphism example
 */
@SubtypeOf(GuardedByUnknown.class) // TODO: Should @GuardSatisfied be in its own hierarchy?
@Documented
@Retention(RetentionPolicy.RUNTIME)
@TargetLocations({ TypeUseLocation.RECEIVER, TypeUseLocation.PARAMETER, TypeUseLocation.RETURN })
@Target(ElementType.TYPE_USE)
public @interface GuardSatisfied {
    /**
     * The index on the GuardSatisfied polymorphic qualifier.
     * Defaults to -1 so that the user can write any index starting from 0.
     */
    int value() default -1;
}