W3cubDocs

/OpenJDK 21

Interface TypeVisitor<R,P>

Type Parameters:
R - the return type of this visitor's methods. Use Void for visitors that do not need to return results.
P - the type of the additional parameter to this visitor's methods. Use Void for visitors that do not need an additional parameter.
All Known Implementing Classes:
AbstractTypeVisitor14, AbstractTypeVisitor6, AbstractTypeVisitor7, AbstractTypeVisitor8, AbstractTypeVisitor9, SimpleTypeVisitor14, SimpleTypeVisitor6, SimpleTypeVisitor7, SimpleTypeVisitor8, SimpleTypeVisitor9, TypeKindVisitor14, TypeKindVisitor6, TypeKindVisitor7, TypeKindVisitor8, TypeKindVisitor9
public interface TypeVisitor<R,P>
A visitor of types, in the style of the visitor design pattern. Classes implementing this interface are used to operate on a type when the kind of type is unknown at compile time. When a visitor is passed to a type's accept method, the visitXyz method most applicable to that type is invoked.

Classes implementing this interface may or may not throw a NullPointerException if the additional parameter p is null; see documentation of the implementing class for details.

API Note:
WARNING: It is possible that methods will be added to this interface to accommodate new, currently unknown, language structures added to future versions of the Java programming language. Such additions have already occurred to support language features added after this API was introduced. Visitor classes directly implementing this interface may be source incompatible with future versions of the platform. To avoid this source incompatibility, visitor implementations are encouraged to instead extend the appropriate abstract visitor class that implements this interface. However, an API should generally use this visitor interface as the type for parameters, return type, etc. rather than one of the abstract classes.

Methods to accommodate new language constructs are expected to be added as default methods to provide strong source compatibility. The implementations of the default methods will in turn call visitUnknown, behavior that will be overridden in concrete visitors supporting the source version with the new language construct.

There are several families of classes implementing this visitor interface in the util package. The families follow a naming pattern along the lines of FooVisitorN where N indicates the source version the visitor is appropriate for. In particular, a FooVisitorN is expected to handle all language constructs present in source version N. If there are no new language constructs added in version N + 1 (or subsequent releases), FooVisitorN may also handle that later source version; in that case, the SupportedSourceVersion annotation on the FooVisitorN class will indicate a later version. When visiting a type representing a language construct introduced after source version N, a FooVisitorN will throw an UnknownTypeException unless that behavior is overridden.

When choosing which member of a visitor family to subclass, subclassing the most recent one increases the range of source versions covered. When choosing which visitor family to subclass, consider their built-in capabilities:

Since:
1.6

Method Summary

Modifier and Type Method Description
default R visit(TypeMirror t)
A convenience method equivalent to visit(t, null).
R visit(TypeMirror t, P p)
Visits a type.
R visitArray(ArrayType t, P p)
Visits an array type.
R visitDeclared(DeclaredType t, P p)
Visits a declared type.
R visitError(ErrorType t, P p)
Visits an error type.
R visitExecutable(ExecutableType t, P p)
Visits an executable type.
R visitIntersection(IntersectionType t, P p)
Visits an intersection type.
R visitNoType(NoType t, P p)
Visits a NoType instance.
R visitNull(NullType t, P p)
Visits the null type.
R visitPrimitive(PrimitiveType t, P p)
Visits a primitive type.
R visitTypeVariable(TypeVariable t, P p)
Visits a type variable.
R visitUnion(UnionType t, P p)
Visits a union type.
R visitUnknown(TypeMirror t, P p)
Visits an unknown kind of type.
R visitWildcard(WildcardType t, P p)
Visits a wildcard type.

Method Details

visit

R visit(TypeMirror t, P p)
Visits a type.
Parameters:
t - the type to visit
p - a visitor-specified parameter
Returns:
a visitor-specified result

visit

default R visit(TypeMirror t)
A convenience method equivalent to visit(t, null).
Implementation Requirements:
The default implementation is visit(t, null).
Parameters:
t - the element to visit
Returns:
a visitor-specified result

visitPrimitive

R visitPrimitive(PrimitiveType t, P p)
Visits a primitive type.
Parameters:
t - the type to visit
p - a visitor-specified parameter
Returns:
a visitor-specified result

visitNull

R visitNull(NullType t, P p)
Visits the null type.
Parameters:
t - the type to visit
p - a visitor-specified parameter
Returns:
a visitor-specified result

visitArray

R visitArray(ArrayType t, P p)
Visits an array type.
Parameters:
t - the type to visit
p - a visitor-specified parameter
Returns:
a visitor-specified result

visitDeclared

R visitDeclared(DeclaredType t, P p)
Visits a declared type.
Parameters:
t - the type to visit
p - a visitor-specified parameter
Returns:
a visitor-specified result

visitError

R visitError(ErrorType t, P p)
Visits an error type.
Parameters:
t - the type to visit
p - a visitor-specified parameter
Returns:
a visitor-specified result

visitTypeVariable

R visitTypeVariable(TypeVariable t, P p)
Visits a type variable.
Parameters:
t - the type to visit
p - a visitor-specified parameter
Returns:
a visitor-specified result

visitWildcard

R visitWildcard(WildcardType t, P p)
Visits a wildcard type.
Parameters:
t - the type to visit
p - a visitor-specified parameter
Returns:
a visitor-specified result

visitExecutable

R visitExecutable(ExecutableType t, P p)
Visits an executable type.
Parameters:
t - the type to visit
p - a visitor-specified parameter
Returns:
a visitor-specified result

visitNoType

R visitNoType(NoType t, P p)
Visits a NoType instance.
Parameters:
t - the type to visit
p - a visitor-specified parameter
Returns:
a visitor-specified result

visitUnknown

R visitUnknown(TypeMirror t, P p)
Visits an unknown kind of type. This can occur if the language evolves and new kinds of types are added to the TypeMirror hierarchy.
Parameters:
t - the type to visit
p - a visitor-specified parameter
Returns:
a visitor-specified result
Throws:
UnknownTypeException - a visitor implementation may optionally throw this exception

visitUnion

R visitUnion(UnionType t, P p)
Visits a union type.
Parameters:
t - the type to visit
p - a visitor-specified parameter
Returns:
a visitor-specified result
Since:
1.7

visitIntersection

R visitIntersection(IntersectionType t, P p)
Visits an intersection type.
Parameters:
t - the type to visit
p - a visitor-specified parameter
Returns:
a visitor-specified result
Since:
1.8

© 1993, 2023, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
https://docs.oracle.com/en/java/javase/21/docs/api/java.compiler/javax/lang/model/type/TypeVisitor.html