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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 evaluates to an integer whose value is less than the lengths of all the
 * given sequences. This annotation is rarely used; it is more common to use {@code @}{@link
 * IndexFor}.
 *
 * For example, an expression with type {@code @LTLengthOf({"a", "b"})} is less than both {@code
 * a.length} and {@code b.length}. The sequences {@code a} and {@code b} might have different
 * lengths.
 *
 * 
The {@code @LTLengthOf} annotation takes an optional {@code offset} element. If it is
 * nonempty, then the annotated expression plus the expression in {@code offset[i]} is less than the
 * length of the sequence specified by {@code value[i]}.
 *
 * 
For example, suppose expression {@code e} has type {@code @LTLengthOf(value = {"a", "b"},
 * offset = {"-1", "x"})}. Then {@code e - 1} is less than {@code a.length}, and {@code e + x} is
 * less than {@code b.length}.
 *
 * 
It is an error to write a {@code LTLengthOf} annotation with a different number of sequences
 * and offsets, if an offset is included.
 *
 * @see IndexFor
 * @checker_framework.manual #index-checker Index Checker
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE_USE, ElementType.TYPE_PARAMETER})
@SubtypeOf(LTEqLengthOf.class)
public @interface LTLengthOf {
  /** Sequences, each of which is longer than the annotated expression's value. */
  @JavaExpression
  public String[] value();

  /**
   * This expression plus the annotated expression is less than the length of the sequence. The
   * {@code offset} element must ether be empty or the same length as {@code value}.
   *
   * The expressions in {@code offset} may be addition/subtraction of any number of Java
   * expressions. For example, {@code @LessThanLengthOf(value = "a", offset = "x + y + 2"}}.
   */
  @JavaExpression
  String[] offset() default {};
}