## Using the Java search engine

Your plug-in can use the JDT API to search Java projects in the workspace for Java elements, such as method references, field declarations, implementors of an interface, etc.

The entry point for Java search is the SearchEngine class. You can search for particular patterns inside a Java element and scope the search to specific elements. Search patterns can be created using createPattern. A pattern is scoped using createJavaSearchScope. Once a pattern and scope are defined, the search method is used to collect the results.

Search results are reported to a SearchRequestor which you must extend in order to access the results.

### Preparing for search

A search operation will use both a pattern for describing the nature of the search, and a scope for restraining the range of investigation.

#### Creating a Java search pattern

A search pattern defines how search results are found. You can either create a search pattern from a Java element (see createPatternPattern(IJavaElement element, int limitTo)) or from a string (see createPattern(String, int, int, int).) The last method supports wildcards (i.e. '*') and can be used to widen the search results.

For example, creating a search pattern for searching for references to a given method is done as follows:

        // Get the method
        IMethod method = ...;

        // Create search pattern
        SearchPattern pattern = SearchPattern.createPattern(method, IJavaSearchConstants.REFERENCES);

Or creating a search pattern for searching for declarations of all types starting with "Obj":

        // Create search pattern
        SearchPattern pattern = SearchPattern.createPattern("Obj*", IJavaSearchConstants.TYPE, IJavaSearchConstants.DECLARATIONS, SearchPattern.R_PATTERN_MATCH | SearchPattern.R_CASE_SENSITIVE);

The following search patterns are supported:

- Package declarations
- Type declarations
- Field declarations
- Method (and constructor) declarations
- Package references
- Type references
- Interface implementors
- Field references
- Field write accesses
- Field read accesses
- Method (and constructor) references
- Combinations of the above patterns using the OR pattern (see createOrPattern)

Note that these patterns are created using the following possible rules:

- R_EXACT_MATCH
- R_PREFIX_MATCH
- R_PATTERN_MATCH
- R_REGEXP_MATCH
- R_CAMELCASE_MATCH
- R_CAMELCASE_SAME_PART_COUNT_MATCH

which may be also combined with one of the following flags:

- R_CASE_SENSITIVE
- R_ERASURE_MATCH
- R_EQUIVALENT_MATCH

For example,

        // a case insensitive prefix match is requested
        SearchPattern pattern1 = SearchPattern.createPattern("Hash", IJavaSearchConstants.TYPE, IJavaSearchConstants.DECLARATIONS, SearchPattern.R_PREFIX_MATCH);

        // a camel case match is requested
        SearchPattern pattern2 = SearchPattern.createPattern("HM", IJavaSearchConstants.TYPE, IJavaSearchConstants.DECLARATIONS, SearchPattern.R_CAMEL_CASE_MATCH);

        // a camel case with a strict expected number of parts match is requested
        SearchPattern pattern3 = SearchPattern.createPattern("HM", IJavaSearchConstants.TYPE, IJavaSearchConstants.DECLARATIONS, SearchPattern.R_CAMELCASE_SAME_PART_COUNT_MATCH);

Note that using the patterns created above reduce the number of possible results among others:

- pattern1: `Hashtable`, `HashMap`, `HashMapEntry`, etc.
- pattern2: `HashMap`, `HashMapEntry`, etc.
- pattern3: `HashMapEntry`, etc.

#### Using fine grain flags in a Java search pattern

Some references patterns can be refined by adding one or several fine grain flags to the `limitTo` parameter.

For example, only the type references used in a cast expression will match the pattern created as follows:

        // Get the type
        IType type = ...;

        // Create search pattern
        SearchPattern pattern = SearchPattern.createPattern(type, IJavaSearchConstants.REFERENCES | IJavaSearchConstants.CAST_TYPE_REFERENCE);

Note that the fine grain flags can be combined together but only for the same kind of search (e.g. only a combination of flags for type references will be meaningful if the `searchFor` parameter is set to TYPE).

Flags for type references

- FIELD_DECLARATION_TYPE_REFERENCE: type references used as the type of a field declaration.
- LOCAL_VARIABLE_DECLARATION_TYPE_REFERENCE: type references used as the type of a local variable declaration.
- PARAMETER_DECLARATION_TYPE_REFERENCE: type references used as the type of a method parameter.
- SUPERTYPE_TYPE_REFERENCE: type references used as a super type or as a super interface.
- THROWS_CLAUSE_TYPE_REFERENCE: type references used in a throws clause.
- CAST_TYPE_REFERENCE: type references used in a cast expression.
- CATCH_TYPE_REFERENCE: type references used in a catch header.
- CLASS_INSTANCE_CREATION_TYPE_REFERENCE: type references used in class instance creation.
- RETURN_TYPE_REFERENCE: type references used as a method return type.
- IMPORT_DECLARATION_TYPE_REFERENCE: type references used in an import declaration.
- ANNOTATION_TYPE_REFERENCE: type references used as an annotation.
- TYPE_ARGUMENT_TYPE_REFERENCE: type references used as a type argument in a parameterized type or a parameterized method.
- TYPE_VARIABLE_BOUND_TYPE_REFERENCE: type references used as a type variable bound.
- WILDCARD_BOUND_TYPE_REFERENCE: type references used as a wildcard bound.
- INSTANCEOF_TYPE_REFERENCE: type references used as an instance of.

Flags for field or method references

- SUPER_REFERENCE: super field accesses or super method invocations (e.g. using the `super` qualifier).
- QUALIFIED_REFERENCE: qualified field accesses or qualified method invocations.
- THIS_REFERENCE: primary field accesses or primary method invocations (e.g. using the `this` qualifier).
- IMPLICIT_THIS_REFERENCE: field accesses or method invocations without any qualification.

#### Creating a Java search scope

If you are interested in search results in a given project or even in a given package, or if you know that search results can only be found in the hierarchy of a given type, you can create the appropriate search scope using createJavaSearchScope(IJavaElement[]) or createHierarchyScope(IType).

For example, creating a search scope on a given package is done as follows:

        // Get the package
        IPackageFragment pkg = ...;

        // Create search scope
        IJavaSearchScope scope = SearchEngine.createJavaSearchScope(new IJavaElement[] {pkg});

Or creating a search scope on the hierarchy of a given type is:

        // Get the type
        IType type = ...;

        // Create search scope
        IJavaSearchScope scope = SearchEngine.createHierarchyScope(type);

Finally, you can create a search scope comprising the entire workspace using createWorkspaceScope:

        // Create search scope
        IJavaSearchScope scope = SearchEngine.createWorkspaceScope();

### Searching

Once you have created a search pattern and a search scope, and you have extended SearchRequestor, you can start a search query as follows:

        // Get the search pattern
        SearchPattern pattern = ...;

        // Get the search scope
        IJavaSearchScope scope = ...;

        // Get the search requestor
        SearchRequestor requestor = ...;

        // Search
        SearchEngine searchEngine = new SearchEngine();
        searchEngine.search(pattern, new SearchParticipant[] {SearchEngine.getDefaultSearchParticipant()}, scope, requestor, null);

A notification that the search starts is sent to your search requestor using the beginReporting method. Then, each search result is reported using the acceptSearchMatch method. Finally endReporting indicates that the search has ended.

### Collecting search results

Search results are reported using the acceptSearchMatch(SearchMatch) method. Paragraphs below highlight some features of SearchMatch.

#### Resources and Java elements

A search result can correspond to a Java element (e.g. a type declaration) or it can be contained in a Java element (e.g. a reference to a type inside a method). The search engine always tries to find the innermost Java element that corresponds to or that contains the search result. For example, searching for references to a method could find such a reference in an initializer. The initializer that contains this method reference is the element of the search match.

The search engine also tries to find the resource that contains the Java element. If the Java element is contained in a compilation unit or a class file, the resource is the corresponding IFile. If the Java element is contained in a .jar file, the returned resource is that .jar file if it is in the workspace, null otherwise.

#### Source positions

Source positions getOffset and getLength are given relative to the compilation unit that contains the search result. If the search result is contained in a .jar file, the source positions are relative to the attached source. They are (-1, -1) if there is no source attached to the .jar file.

#### Accurate versus inaccurate search results

In most cases search results are accurate, meaning that the search engine was able to determine that the given match is what was asked for. However in some cases the search engine is unable to do so, in such cases the match is inaccurate. Some possible reasons why a match could be inaccurate are:

- The classpath on the project that contains the result is not properly set. For example, it refers to a project that is not accessible, a jar on the classpath requires another jar that is not on the classpath, etc.
- The user code would not compile. For example, it refers to a class that is not yet defined.