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I'm trying to access a document class that has id, name, text and list of words. I try to compare id which I have with the ids and when found get the list of words attached to this id to find exact word. I was trying with java reflection but I'm unable to get it working?
Any help is highly appreciated. 

public class Doc { private static int documentID; private static Doc docInstance = null; private String documentText; private ArrayList<String> listOfTokens; static int docCount = 0; public Doc() { documentID = 0; listOfTokens = new ArrayList<String>(); tokFreq = 0; docCount++; } public static Doc getDocInstance() { if (docInstance == null) { docInstance = new Doc(); } return docInstance; } public ArrayList<String> getListOfTokens() { return listOfTokens; } }

and I am trying this

public static void createDocumentVector(TreeMap<Integer,Integer> documentVector, TreeMap<String, ArrayList<Integer>>qm, int N) throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException { int eachDoc = 0; Collection<String> allKeys = qm.keySet(); ArrayList<Integer> l1 = new ArrayList<Integer>(); boolean addedTerm = false; /** Obtain an Iterator for Collection */ Iterator<String> itr = allKeys.iterator(); String key; int termFrequency = 0; int documentFrequency = 0; /** Iterate through TreeMap values iterator */ while(itr.hasNext()) { key = (String)itr.next(); Integer LL = 0; l1 = qm.get(key); // Returns value of that key for (int k = 0; k < l1.size(); k++) { LL = l2.get(k); Doc obj = new Doc(); Class<? extends Doc> docOb = obj.getClass(); Field field1 = docOb.getDeclaredField("documentID"); field1.setAccessible(true); Field field2 = docOb.getDeclaredField("listOfTokens"); field1.setAccessible(true); if (field1.isAccessible()) { Method setID = docOb.getDeclaredMethod("setDocumentID", new Class[]{int.class}); setID.setAccessible(true); setID.invoke(docOb, LL); } Method listTock = docOb.getMethod("getListOfTokens"); ArrayList<String> per = (ArrayList<String>) listTock.invoke(docOb, null); for (String tock : per) { if(tock.equals(key)) { termFrequency++; } } documentFrequency = l1.size(); eachDoc.add(getTFIDF(termFrequency, documentFrequency, N)); documentVector.put(eachDoc, LL); addedTerm = true; } } }

And I get this error

Exception in thread "main" java.lang.IllegalArgumentException: object is not an instance of declaring class at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source)
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  • It might be a good idea to ask for a code review on codereview.stackexchange.com, I'm seeing quite a few things that seem a little unusual in the code you posted. They aren't specific to the error you're seeing, just general items. Commented Jun 30, 2016 at 3:13
  • Any reason why you are using reflection on this simple task? You are explicitly creating a Doc instance after all. Commented Jul 4, 2016 at 2:04
  • OK, maybe i wont implement Reflection anymore here! Any suggestions??, since doc class has nothing to holdall docs ids. Maybe i should add hashmap to store doc ids and their list of tockens?? Commented Jul 4, 2016 at 10:55

2 Answers 2

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TreeMap<List<Integer>,Integer> causes an error, due to this explanation in the javadoc.

The map is sorted according to the {@linkplain Comparable natural ordering} of its keys

But List does not implement the Comparable interface. So you can't use List<Integer> as a key in a TreeMap.

My English is poor, hope you can understand!

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I know that, and I changed it but still getting same error!! Any suggestions please..
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Did you post the complete definition of Doc? It's missing the setDocumentID method.

Anyway, I was able to reproduce your error with the following code:

public class DocReflection { private static int documentId; // static field private void setDocumentId(int docId) { // but setter is not static. documentId = docId; } public static void main(String [] args) throws NoSuchFieldException, NoSuchMethodException, InvocationTargetException, IllegalAccessException { DocReflection docReflection = new DocReflection(); Class<? extends DocReflection> cls = docReflection.getClass(); Field docId = cls.getDeclaredField("documentId"); docId.setAccessible(true); if (docId.isAccessible()) { Method setId = cls.getDeclaredMethod("setDocumentId", new Class[]{int.class}); setId.setAccessible(true); setId.invoke(cls, 1); // <-- Invoking non-static method with class object. } } }

Output:

Exception in thread "main" java.lang.IllegalArgumentException: object is not an instance of declaring class at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at com.company.DocReflection.main(DocReflection.java:28) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

Solution is to make setDocumentId static.

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