Javadoc (originally cased JavaDoc) is a documentation generator created by Sun Microsystems for the Java language (now owned by Oracle Corporation) for generating APIdocumentation in HTML format from Java source code. The HTML format is used for adding the convenience of being able to hyperlink related documents together.
The “doc comments” format used by Javadoc is the de facto industry standard for documenting Java classes. Some IDEs, like IntelliJ IDEA, NetBeans and Eclipse, automatically generate Javadoc HTML. Many file editors assist the user in producing Javadoc source and use the Javadoc info as internal references for the programmer.
Javadoc also provides an API for creating doclets and taglets, which allows users to analyze the structure of a Java application. This is how JDiff can generate reports of what changed between two versions of an API.
Javadoc does not affect performance in Java as all comments are removed at compilation time. Writing comments and Javadoc is for better understanding the code and thus better maintaining it.