This is probably a regression caused by 
http://hg.netbeans.org/main/rev/27dc0e1e31ee

and specifically, these three lines:

+ if(JsModel.isGeneratedIdentifier(node.getString())) {
+ continue;
+ } 

Marek, in this case, node will be Token.REGEXP, Token.FUNCNAME, or Token.OBJLITNAME, and a regexp cannot be cast to a
StringNode (which is what node.getString does.  Yes, the Rhino AST is a bit weird - it defines a getString method which
throws an exception if the method is called on a node type which doesn't support it).

I'm bumping the priority on this since it shows up when you open pretty much any large file (any file containing a regexp).

(I can fix this on Friday if you don't get to it sooner - I'm on my way out the door. There's a unit test for
JsSemanticAnalyzer so you should be able to use it to verify the bug.)

This issue has already 5 duplicates 

Edited
/**
 * Helps to compose blocks of text.
 */
function TextBlock(){
    this.text="";
    /**
     * Adds text as new line.
     */
    this.addLine=function(text){
        this.text+=text+"\n";
    }
    /**
     * Adds block of text.
     */
    this.addText=function(text){
        this.text+=text;
    }
    /**
     * Returns accumulated text.
     */
    this.getText=function(){
        return this.text;
    }
}

function Template(template){
    this.template=template;
    this.params=new Array();
    this.setParameter=function(name,value){
        this.params[name]=new Array();
        this.params[name]["name"]=name;
        this.params[name]["value"]=value;
    }
    this.eval=function(){
        result=this.template;
        for(param in this.params){
            result.replace(/this.params[param]["name"]/g,this.params[param]["value"]);
                
                this.params[param]["name"]+" -> "+this.params[param]["value"]+"\n";
        }
        return result;
    }
}

/**
 * Represents Java source file.
 */
function JavaSource(){
    this.packageName="";
    this.imports=new Array();
    this.declaration="";
    this.body="";
    this.addImport=function(importName){
        this.imports.push(importName);
    }
    this.getImports=function(){
        result = new TextBlock();
        for(importName in this.imports){
            result.addLine("import "+this.imports[importName]+";");
        }
        return result.getText();
    }
}
source= new JavaSource();
source.addImport("org.a");
source.addImport("org.b");
source.getImports();

Created attachment 61466 [details]
ide log

fixed in revision a000a5ddcd39

- if(JsModel.isGeneratedIdentifier(node.getString())) {
+ if(node.isStringNode() && JsModel.isGeneratedIdentifier(node.getString())) {

though I didn't check the node's instance by type (int) creation so it may never be true even for Token.FUNCNAME, or
Token.OBJLITNAME. Please correct if necessary.

I am sorry for the regression.

Integrated into 'main-golden', available in NB_Trunk_Production #206 build
Changeset: http://hg.netbeans.org/main/rev/a000a5ddcd39
User: Marek Fukala <mfukala@netbeans.org>
Log: #135153 - ClassCastException: org.mozilla.javascript.Node cannot be cast to org.mozilla.javascript.Node$StringNode