FULL PRODUCT VERSION :


ADDITIONAL OS VERSION INFORMATION :
Ubuntu Linux

A DESCRIPTION OF THE PROBLEM :
This code can be compiled by Java8 javac, but not by Java9 javac:

import javax.swing.tree.DefaultMutableTreeNode;
import java.util.List;

public class MyNode extends DefaultMutableTreeNode {

    public int countChildren() {
        return ((List<MyNode>) children).size();
    }

}

REGRESSION. Last worked in version 9


REPRODUCIBILITY :
This bug can be reproduced always.