Java Annotation Processor getEnclosingElement() method

Question

Hello，I would like to ask what is the meaning of the comments of the getEnclosingElement() method in the Element interface, I do not quite understand. javadoc as follows：

Returns the innermost element within which this element is, loosely speaking, enclosed.

If this element is one whose declaration is lexically enclosed immediately within the declaration of another element, that other element is returned.

If this is a top-level type, its package is returned.

If this is a package, null is returned.

If this is a type parameter, the generic element of the type parameter is returned.

If this is a method or constructor parameter, the executable element which declares the parameter is returned.

Annotations can be used on classes, variables (global or local), methods, etc., but I don't know the correspondence between annotations and Element subclass. Thanks!!!

Slaw · Accepted Answer · 2020-03-07T08:26:11.477

An Element can represent, as of Java 13:

A module declaration - ModuleElement
A package declaration - PackageElement
An interface, class, enum, or annotation type - TypeElement
A constructor, method, or initializer - ExecutableElement
A field, enum constant, method or constructor parameter, local variable, resource variable, or exception parameter - VariableElement
A type parameter - TypeParameterElement

Each of these elements can have annotations present. For example:

module-info.java:

@Foobar
module example {
  exports com.example;
}

package-info.java:

@Foobaz
package com.example;

Foo.java:

package com.example;

@Baz
public class Foo<@Qux T> {

  private final T bar;

  public Foo(T bar) {
    this.bar = bar;
  }

  @Override
  public String toString() {
    return "Foo{bar= " + bar + "}";
  }
}

The module example, which would be a ModuleElement, has a @Foobar annotation present.
The package com.example, which would be a PackageElement, has a @Foobaz annotation present.
The class Foo, which would be a TypeElement, has a @Baz annotation present.
The type parameter T, which would be a TypeParameterElement, has a @Qux annotation present.
The field bar, which would be a VariableElement, has no annotations present.
The constructor #Foo(T), which would be an ExecutableElement, has no annotations present.
The constructor's parameter bar, which would be a VariableElement, has no annotations present.
The method #toString(), which would be an ExectuableElement, has an @Override annotation present.

You can get the annotations present on these elements via the methods of the AnnotatedConstruct interface, which Element extends.

The method Element#getEnclosingElement() returns, unsurprisingly, the Element which encloses the current Element, if any. So if you were to invoke that method on the ExecutableElement representing the method #toString() then you'd get the TypeElement representing the class Foo.

Java Annotation Processor getEnclosingElement() method

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