Entries in a HashMap being overwritten by completely different keys?

I have a Java HashMap used to store some basic string values:

Map<String, String> map = new HashMap<String, String>();
map.put("Id", task.getStorageId());
map.put("Name", task.getName());
map.put("Description", task.getDescription());

Under one usage, the Id entry is overwitten by the Description entry, everytime without fail. I have watched it in the debugger - Id is inserted fine, Name inserted fine, then when Descroption is inserted, it overwrites the Id entry. Using exactly the same code and keys in another p开发者_JAVA百科art of the application it works with no problems. Totally confused. What is going on here?

Edit

Perhaps I should have mentioned (though it didn't seem relevant), this is happening on Android, not in a JVM. Could that be the issue? I also found it hard to believe but the chunk of code is as simple as the snippet provided. I will try to bundle an Android app that demonstrates it and post somewhere.

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It is likely that the entry you are not seeing is there, look at the modCount for the table and you should see the proper number of entries. This means that a hash collision has occurred. Basically 2 keys got hashed into the same bucket in the table. If you look at the bucket that had the original key it has a next field, which is a pointer to the other entry that you think you have lost.

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That should in no way be happening. The HashMap uses a key's hashCode() method to index the Map's entries. Since

"Id".hashCode() == "Description".hashCode()

is false (yes, I just tested it for sanity), the put(String, String) operations are not interfering. Do some more inspection and make sure your code is really the same as what you posted above.

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Maybe the code you debug and the sources you use are not in sync? Maybe you have changed your sources but havn't compiled correctly? Perhaps you have a jar with an old version of your softwar eon your classpath?

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Not happening to me:

import java.util.Map;
import java.util.HashMap;

public class MapDemo
{
   public static void main(String[] args)
   {
      Map<String, String> map = new HashMap<String, String>();
      map.put("Id", "task.getStorageId()");
      map.put("Name", "task.getName()");
      map.put("Description", "task.getDescription()");

      System.out.println("map: " + map);
   }
}

Here's the output:

com.intellij.rt.execution.application.AppMain MapDemo
map: {Name=task.getName(), Description=task.getDescription(), Id=task.getStorageId()}

Process finished with exit code 0

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I had the same experience and in debugging it looked like an entry is overwritten by a completely different entry. When i tried to retrieve the value it returned null.

But it was because, when retrieving I had used simplecase value as key. When used the exact format, value was returning properly.

eg:

  map.put("A", "value1");
  map.put("B", "value2");
  map.put("C", "value3");

  map.get(a) --> null
  map.get(A) --> value1