Java Community | Help. Code. Learn.•3w ago

Week 102 — What is the `package-info.java` file and what can be done with it?

Question of the Week #102

What is the package-info.java file and what can be done with it?

2 Replies

The package-info.java can be used to provide Javadoc documentation for a package. After creating a package-info.java file in some package, one would typically add a Javadoc comment followed by a package declaration stating the package the file is located in.

/**
* This is my package.
+ It can do a lot of stuff.
* Obviously, this should be a proper documentation instead of this sample text.
*/
package com.example.mypackage;

/**
* This is my package.
+ It can do a lot of stuff.
* Obviously, this should be a proper documentation instead of this sample text.
*/
package com.example.mypackage;

The javadoc tool will recognize this file and include the Javadoc comment in the generated documentation.

Eric McIntyre•3w ago

This file can also be used to add annotations to a package. For example, assume an annotation com.example.annotations.MyAnnotation with the PACKAGE target:

package com.example.annotations;

import java.lang.annotation.*;

@Retention(RetentionPolicy.SOURCE)
@Target(ElementType.PACKAGE)
public @interface MyAnnotation{

}

package com.example.annotations;

import java.lang.annotation.*;

@Retention(RetentionPolicy.SOURCE)
@Target(ElementType.PACKAGE)
public @interface MyAnnotation{

}

This annotation can be used in a package-info.java file before the package declaration. Annotations in the package-info.java can be imported after the package declaration:

@MyAnnotation
package com.example.mypackage;

import com.example.annotations.MyAnnotation;

@MyAnnotation
package com.example.mypackage;

import com.example.annotations.MyAnnotation;

Annotations like these are considered to annotate the package. An example of this is the @NullMarked annotation in jspecify that can be applied on packages and modules among other elements.

@NullMarked
package com.example.mypackage;

import org.jspecify.NullMarked;

@NullMarked
package com.example.mypackage;

import org.jspecify.NullMarked;

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Week 102 — What is the `package-info.java` file and what can be done with it?