To old files I don't know how to do it... I think you will need a script to go thru all files and add the header.
To change the new ones you can do this.
Go to Eclipse menu bar
- Window menu.
- Preferences
- search for Templates
- go to Code templates
- click on +code
- Click on New Java files
- Click Edit
- add
/**
${user}
*/
And it's done every new File will have your name on it !