To set the maximum line length in Eclipse, open Eclipse and in the menu bar, go to Window -> Preferences and in the pop-up window, go to Java -> Code Style -> Formatter.
This will open up the Formatter options in the right window pane. Click on the Edit button to modify the current formatter profile.
In the formatter profile pop-up window, click on the Line Wrapping tab. The width of the line can be set in field, Maximum line width.
Changing any of the [built-in] profiles requires to save the changes as a custom profile. More details about how to do this can be found in my blog, How to create and share Eclipse code style formatter
How to set maximum line length in eclipse