Javadoc Search Specification

This document specifies the behaviour of the Javadoc search feature for JDK 21.

Overview

The Javadoc search feature was introduced in JDK 9 with JEP 225. However, the initial specification only contained a very basic description of the search algorithm. As a consequence, selection and ranking of search results sometimes left a bit to be desired.

The purpose of this additional specification is to improve on the initial implementation by defining better rules for the selection and ranking of search results.

Definitions

The term entity is used to describe an artifact of the documented code, which includes code elements as well as additional search tags.

The term signature is used to describe how an entity is represented in Javadoc search.

The terms name and identifier are used as defined in Java Language Specification, Section 6.2.

The terms white space and separator are used as defined in Java Language Specification, Section 3.6 and Section 3.11.

The term camel-case is used to describe mixed case identifiers that make use of uppercase letters to mark word boundaries within the identifier.

The term query string is used to describe the characters entered in the search input box by the user.

All examples in the following sections refer to or are taken from the standard OpenJDK class libraries.

Searchable Entities

The list below describes the entities of documented code and how their signatures are built. For some elements, the signature consists of just the entity's name, while for others it contains information about containing entities or types of parameters.

Modules

The signature of a module equals the module name.

Example: - java.base

Packages

The signature of a package consists of the package name.

If the package belongs to a named module, the module name is prepended to the signature separated by / and can be included in the search.

Example: - java.base/java.util.concurrent

Types

The signature of a type (classes, interfaces, enums, annotation types) consists of the type name.

If the type is a nested type, names of parent types are prepended to the signature separated by . and can be included in the search.

If the type is contained in a package, the package name is prepended to the signature separated by . and can be included in the search.

Examples: - java.lang.Object - java.util.Map.Entry

Members

The signature of a member (methods, constructors, fields) consists of the member name prepended with its defining type, separated by ..

If the member is a method or constructor, the type names of parameters are appended to the name enclosed between ( and ) and separated by , to identify overloaded methods.

Examples: - java.lang.Object.wait(long, int) - java.lang.String.String(String) - java.lang.Byte.MAX_VALUE

Search Tags

Search Tags are arbitrary searchable items defined using the @index tag anywhere in a Javadoc comment of the documented source code.

Examples: - {@index "Java Collections Framework"} - {@index jrt jrt}

Matching Rules

The following sections describe the special rules under which the query string is matched against the entity signatures.

Case Sensitivity

If the query string does not contain any uppercase characters, the search is performed in a case insensitive manner. If the query string contains uppercase characters, results with matching capitalization are considered better matches and shown before results with non-matching capitalization. Additionally, the rules described in the Camel Case Matches section are applied.

Left Boundaries

The beginning of the query string must match a left word boundary, or a separator preceding a left word boundary.

The following are considered left word boundaries:

• The beginning of an identifier
• An uppercase letter within a camel-case identifier
• The character following a _ within an identifier

Partial Matches

The query string matches an identifier even if characters at the end of a name identifiers are missing, as long as the query string matches the beginning of the identifier.

Camel Case Matches

The rule for partial matches also applies to uppercase characters followed by any number of lowercase or non-letter characters within a camel-case identifier.

An uppercase character in the query string followed by zero or more lowercase or non-letter characters matches the exact same character sequence in an entity's signature, followed by zero or more lowercase or non-letter characters.

White Space and Multiple Search Terms

If a query string contains space characters, the parts of the query string delimited by space characters are considered search terms. The following three conditions must be true for an entity to match a query string consisting of multiple search terms:

• All search terms must match the entity's signature.
• Search terms must match the entity's signature in the order in which they appear in the query string.
• The match for each search term must be aligned with a left word boundary in the entity's signature as defined in the Left Boundaries section.

Multiple consecutive space characters are considered equivalent to a single space character. If the query string consists entirely of white space no search is performed.

Core and Peripheral Matches

The part of an entity's signature that represents the entity's name is considered the core component of the signature, while any other parts of the signature are considered peripheral components.

An entity will only be included in the search result if the query string contains and matches at least part of its core component.

Although the parameter types of a method or constructor are not considered a core component of its signature, it is possible to search for methods or constructors with specific parameter types by starting the search string with (.

Accessing Child Elements

A query string that matches a code element can be turned into a search string that matches the element's child elements by appending the separator used to connect the two levels of code elements.

Ranking of Results

A result that matches a whole identifier is ranked higher than a match that covers only part of an identifier, such as a segment of a camel-case identifier starting with a capital letter, or the beginning of an identifier. The result matching the whole identifier will appear higher up in the list of search results.

Examples:

• Query string set matches types java.util.Set and java.util.HashSet but the former is ranked higher than the latter.
• Query string java.lang.ref matches both packages java.lang.ref and java.lang.reflect but the former is ranked higher than the latter because it matches the whole package name.

Results from case-sensitive searches are ranked higher than results from case-insensitive searches when both a case-sensitive and a case-insensitive search is performed.

Supported Browsers

The search feature is supported in the following browsers.