First, we can not edit some files which size are large, more than 20M or
even larger according to the default config in eclipse. Or there is
java.lang.OutOfMemoryError.
Second, there is a plugin project.In the project,here is an editer which
extends "org.eclipse.ui.editors.text.FileDocumentProvider" and there can
not be able to edit some larger files because of needing more java heap
space.