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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.index.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;

/**
 * The annotated expression is between {@code -1} and {@code -a.length - 1}, inclusive, for each
 * sequence {@code a} listed in the annotation.
 *
 * This type should rarely (if ever) be written by programmers. It is inferred by the
 * SearchIndexChecker when the result of a call to one of the JDK's binary search methods (like
 * {@code Arrays.binarySearch}) is known to be less than zero. For example, consider the following
 * code:
 *
 * 
 *
 *     int index = Arrays.binarySearch(array, target);
 *     if (index < 0) {
 *          // index's type here is @NegativeIndexFor("array")
 *          index = index * -1;
 *          // now index's type is @IndexFor("array")
 *     }
 * 
 *
 * @checker_framework.manual #index-checker Index Checker
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE_USE, ElementType.TYPE_PARAMETER})
@SubtypeOf(SearchIndexFor.class)
public @interface NegativeIndexFor {
  /**
   * Sequences for which this value is a "negative index"; that is, the expression is in the range
   * {@code -1} to {@code -a.length - 1}, inclusive, for each sequence {@code a} given here.
   */
  @JavaExpression
  public String[] value();
}