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TypeVisitor.java
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TypeVisitor.java
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/*
* Copyright (c) 2005, 2017, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package javax.lang.model.type;
/**
* 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 {@link TypeMirror#accept accept} method, the <code>visit<i>Xyz</i></code>
* method most applicable to that type is invoked.
*
* <p> Classes implementing this interface may or may not throw a
* {@code NullPointerException} if the additional parameter {@code p}
* is {@code null}; see documentation of the implementing class for
* details.
*
* <p> <b>WARNING:</b> 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. Therefore, 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.
*
* <p>Note that methods to accommodate new language constructs could
* be added in a source <em>compatible</em> way if they were added as
* <em>default methods</em>. However, default methods are only
* available on Java SE 8 and higher releases and the {@code
* javax.lang.model.*} packages bundled in Java SE 8 were required to
* also be runnable on Java SE 7. Therefore, default methods
* were <em>not</em> used when extending {@code javax.lang.model.*}
* to cover Java SE 8 language features. However, default methods
* are used in subsequent revisions of the {@code javax.lang.model.*}
* packages that are only required to run on Java SE 8 and higher
* platform versions.
*
* @param <R> the return type of this visitor's methods. Use {@link
* Void} for visitors that do not need to return results.
* @param <P> the type of the additional parameter to this visitor's
* methods. Use {@code Void} for visitors that do not need an
* additional parameter.
*
* @author Joseph D. Darcy
* @author Scott Seligman
* @author Peter von der Ahé
* @since 1.6
*/
// 类型访问器,可以对不同的类型执行相应的操作
public interface TypeVisitor<R, P> {
/**
* Visits a type.
*
* @param t the type to visit
* @param p a visitor-specified parameter
*
* @return a visitor-specified result
*/
// 任意类型
R visit(TypeMirror t, P p);
/**
* Visits a primitive type.
*
* @param t the type to visit
* @param p a visitor-specified parameter
*
* @return a visitor-specified result
*/
// 基本类型
R visitPrimitive(PrimitiveType t, P p);
/**
* Visits the null type.
*
* @param t the type to visit
* @param p a visitor-specified parameter
*
* @return a visitor-specified result
*/
// null
R visitNull(NullType t, P p);
/**
* Visits an array type.
*
* @param t the type to visit
* @param p a visitor-specified parameter
*
* @return a visitor-specified result
*/
// 数组类型
R visitArray(ArrayType t, P p);
/**
* Visits a declared type.
*
* @param t the type to visit
* @param p a visitor-specified parameter
*
* @return a visitor-specified result
*/
// 声明类型,如类或接口
R visitDeclared(DeclaredType t, P p);
/**
* Visits an error type.
*
* @param t the type to visit
* @param p a visitor-specified parameter
*
* @return a visitor-specified result
*/
// 错误类型
R visitError(ErrorType t, P p);
/**
* Visits a type variable.
*
* @param t the type to visit
* @param p a visitor-specified parameter
*
* @return a visitor-specified result
*/
// 类型变量
R visitTypeVariable(TypeVariable t, P p);
/**
* Visits a wildcard type.
*
* @param t the type to visit
* @param p a visitor-specified parameter
*
* @return a visitor-specified result
*/
// 通配符
R visitWildcard(WildcardType t, P p);
/**
* Visits an executable type.
*
* @param t the type to visit
* @param p a visitor-specified parameter
*
* @return a visitor-specified result
*/
// 可执行类型,如方法、构造器、初始化块
R visitExecutable(ExecutableType t, P p);
/**
* Visits a {@link NoType} instance.
*
* @param t the type to visit
* @param p a visitor-specified parameter
*
* @return a visitor-specified result
*/
// 代表没有合适的类型与之对应
R visitNoType(NoType 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 {@code TypeMirror} hierarchy.
*
* @param t the type to visit
* @param p a visitor-specified parameter
*
* @return a visitor-specified result
*
* @throws UnknownTypeException a visitor implementation may optionally throw this exception
*/
// 未知类型
R visitUnknown(TypeMirror t, P p);
/**
* Visits a union type.
*
* @param t the type to visit
* @param p a visitor-specified parameter
*
* @return a visitor-specified result
*
* @since 1.7
*/
// 联合类型,如多个异常类型联合使用 ExceptionA | ExceptionB e
R visitUnion(UnionType t, P p);
/**
* Visits an intersection type.
*
* @param t the type to visit
* @param p a visitor-specified parameter
*
* @return a visitor-specified result
*
* @since 1.8
*/
// 交集类型,如 Number & Runnable
R visitIntersection(IntersectionType t, P p);
/**
* A convenience method equivalent to {@code visit(t, null)}.
*
* @param t the element to visit
*
* @return a visitor-specified result
*
* @implSpec The default implementation is {@code visit(t, null)}.
*/
default R visit(TypeMirror t) {
return visit(t, null);
}
}