Hashtable<String, Object> not finding strings

Question

I have a Hashtable of type Hashtable

I've loaded several strings as keys, one of which is "ABCD"

However, later when I go to look up "ABCD", the Hashtable returns null instead of the associated object. Further the keyset contains "ABCD", but a request to containsKey("ABCD") returns false.

Is this because String objects are inherently different objects?

If so, what is the write way to store information in a Hashtable if I want to use Strings as keys?

 public class Field {
        private String name;
        private DataType dataType;

        public Field(String name, DataType dataType) {
            this.name = name;
            this.dataType = dataType;
        }

        public String getName() {
            return name;
        }

        public DataType getDataType() {
            return dataType;
        }

        public String toString() {
            return name;
        }
    }

public class Record {
        private Hashtable<String, Data> content; 

        public Record(Field[] fieldList) {
            this.fieldList = fieldList;     
            content = new Hashtable<String, Data>();

            System.out.println(fieldList.length);

            for(Field f : fieldList) {          
                content.put(f.getName(), new Data());
            }
        }

        public void add(String field, String s) {
                    // ERROR OCCURS HERE IN THIS METHOD !!!

            System.out.println(field);

            for(String ss : content.keySet()) {
                System.out.print(" [ " + ss + " ] ");
            }
            System.out.println();

            System.out.println(content.containsKey(field));     
            System.out.println(content.get(field));

            content.get(field).add(s);
        }
}



public class Data {

    private Vector<String> lines;
    private int index;

    public Data() {
        lines = new Vector<String>();
        index = 0;
    }

    public void add(String s) {
        System.out.println("adding");
        lines.add(s);
    }

    public String nextLine() {
        try {
            return lines.elementAt(index++);
        } catch (ArrayIndexOutOfBoundsException aioobe) {
            return null;
        }
    }
}

Solution

Works for me!

import java.util.Hashtable;

public class StrMap {
    public static void main(String[] args) {
        Hashtable<String,Object> map = new Hashtable<String,Object>();
        map.put("ABCD", "value");
        System.err.println(map.containsKey("ABCD"));
    }
}

Yo have probably made some other error. Reduce the problem to the smallest complete compilable program that still demonstrates the problem. You'll probably find the problem straight away. If you don't, at least you will have a question that we can answer.

(Also Map and HashMap is that way to go. Hashtable is useful if you are using a pre-Java 2 API (Java 2 is comfortably over a decade old now!).)

Comments

[Kirk]

Again, I started with the HashMap

[BalusC]

I said, unrelated to the actual problem. Follow the three common causes. Check the outcome of System.out.println(content) before using it, check if the String is in right case and it doesn't contain surrounding whitespace. They have to be an exact match.

[Andrzej Doyle]

+1: Agree that the code looks fine. Perhaps this is an issue with invisible whitespace, similar Unicode characters or something such that the table contains a key that appears to be the same but is a separate sequence of characters. Also yes, definitely use a Map for this!

[barrowc]

If you have the same issue with HashTable as you did with HashMap then you may as well go back to using HashMap

[Kirk]

There was whitespace for some reason and I was having a hard time seeing it where it was... silly me.

[ankitjaininfo]

+1. i did check my code/logic. I was calling hashTbl.contains() instead of hashTbl.containsKey() ! why there are three: contains() containsKey() and containsValue(). i see there is need for two only.

[Brett]

@Ankit Jain containsKey and containsValue are from Map. contains is for compatibility with pre-1.2 Java.