I was looking for the source code of com.intellij.openapi.graph.base.Command class here
https://github.com/JetBrains/intellij-community
,but it doesn't contain com.intellij.openapi.graph.base package.
Where can I find it ?
Unfortunately, these sources are not available.
Taken from here
DEA's visualization support uses yFiles which is a commercial product, and therefore it's not available in the Community Edition. In the Ultimate edition, you can use yFiles in your plugins by means of IDEA's wrapper classes (the com.intellij.openapi.graph package). There's no documentation for it, but it essentially mirrors the yFiles API.
We're no longer publishing javadocs as a separate download: you can simply refer to the Community Edition source for any necessary information.