com.google.auto.common.MoreElements Maven / Gradle / Ivy

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/*
 * Copyright (C) 2013 Google, Inc.
 * Copyright (C) 2013 Square, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.auto.common;

import static javax.lang.model.element.ElementKind.PACKAGE;

import com.google.common.annotations.Beta;

import javax.lang.model.element.Element;
import javax.lang.model.element.ElementVisitor;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.PackageElement;
import javax.lang.model.element.TypeElement;
import javax.lang.model.element.VariableElement;
import javax.lang.model.util.Elements;
import javax.lang.model.util.SimpleElementVisitor6;

/**
 * Static utility methods pertaining to {@link Element} instances.
 *
 * @author Gregory Kick
 */
@Beta
public final class MoreElements {
  /**
   * An alternate implementation of {@link Elements#getPackageOf} that does not require an
   * {@link Elements} instance.
   *
   * @throws NullPointerException if {@code element} is {@code null}
   */
  public static PackageElement getPackage(Element element) {
    while (element.getKind() != PACKAGE) {
      element = element.getEnclosingElement();
    }
    return (PackageElement) element;
  }

  private static final ElementVisitor PACKAGE_ELEMENT_VISITOR =
      new SimpleElementVisitor6() {
        @Override protected PackageElement defaultAction(Element e, Void p) {
          throw new IllegalArgumentException();
        }

        @Override public PackageElement visitPackage(PackageElement e, Void p) {
          return e;
        }
      };

  /**
   * Returns the given {@link Element} instance as {@link PackageElement}.
   *
   * This method is functionally equivalent to an {@code instanceof} check and a cast, but should
   * always be used over that idiom as instructed in the documentation for {@link Element}.
   *
   * @throws NullPointerException if {@code element} is {@code null}
   * @throws IllegalArgumentException if {@code element} isn't a {@link PackageElement}.
   */
  public static PackageElement asPackage(Element element) {
    return element.accept(PACKAGE_ELEMENT_VISITOR, null);
  }

  private static final ElementVisitor TYPE_ELEMENT_VISITOR =
      new SimpleElementVisitor6() {
        @Override protected TypeElement defaultAction(Element e, Void p) {
          throw new IllegalArgumentException();
        }

        @Override public TypeElement visitType(TypeElement e, Void p) {
          return e;
        }
      };

  /**
   * Returns the given {@link Element} instance as {@link TypeElement}.
   *
   * 
This method is functionally equivalent to an {@code instanceof} check and a cast, but should
   * always be used over that idiom as instructed in the documentation for {@link Element}.
   *
   * @throws NullPointerException if {@code element} is {@code null}
   * @throws IllegalArgumentException if {@code element} isn't a {@link TypeElement}.
   */
  public static TypeElement asType(Element element) {
    return element.accept(TYPE_ELEMENT_VISITOR, null);
  }

  private static final ElementVisitor VARIABLE_ELEMENT_VISITOR =
      new SimpleElementVisitor6() {
        @Override protected VariableElement defaultAction(Element e, Void p) {
          throw new IllegalArgumentException();
        }

        @Override public VariableElement visitVariable(VariableElement e, Void p) {
          return e;
        }
      };

  /**
   * Returns the given {@link Element} instance as {@link VariableElement}.
   *
   * 
This method is functionally equivalent to an {@code instanceof} check and a cast, but should
   * always be used over that idiom as instructed in the documentation for {@link Element}.
   *
   * @throws NullPointerException if {@code element} is {@code null}
   * @throws IllegalArgumentException if {@code element} isn't a {@link VariableElement}.
   */
  public static VariableElement asVariable(Element element) {
    return element.accept(VARIABLE_ELEMENT_VISITOR, null);
  }

  private static final ElementVisitor EXECUTABLE_ELEMENT_VISITOR =
      new SimpleElementVisitor6() {
        @Override protected ExecutableElement defaultAction(Element e, Void p) {
          throw new IllegalArgumentException();
        }

        @Override public ExecutableElement visitExecutable(ExecutableElement e, Void p) {
          return e;
        }
      };

  /**
   * Returns the given {@link Element} instance as {@link ExecutableElement}.
   *
   * This method is functionally equivalent to an {@code instanceof} check and a cast, but should
   * always be used over that idiom as instructed in the documentation for {@link Element}.
   *
   * @throws NullPointerException if {@code element} is {@code null}
   * @throws IllegalArgumentException if {@code element} isn't a {@link ExecutableElement}.
   */
  public static ExecutableElement asExecutable(Element element) {
    return element.accept(EXECUTABLE_ELEMENT_VISITOR, null);
  }

  private MoreElements() {}
}