Android : Android Object not locked by thread

I have made a function in my app to delete a record from a database. I am using a seperate activity to do my deleting. When i enter in the row id to be deleted my app tells me that the app has stopped working, but when i click ok it returns me to the main activity screen. I am using a notifyAll() function to update the database and the list view that I have on the main activity, I think this is where its going wrong but I cant figure out why as I am still quite new to android.

this is the activity where i am using the notifyAll()

package com.example.rory.dbtest;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.pinchtapzoom.R;


public class Delete extends Activity implements View.OnClickListener{

public EditText edit1;
Button delete;

DBAdapter db = new DBAdapter(this);


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_delete);

    edit1 = (EditText)findViewById(R.id.edit1);
    delete = (Button)findViewById(R.id.deleteBtn);

    delete.setOnClickListener((View.OnClickListener) this);

    }


public void onClick(View v) {

    String userInput = edit1.getText().toString();

    //if the ROW ID its a number (long)
    try{
        long rowID = Long.parseLong(userInput);
        //call the delete method
        db.open();
        db.deleteContact(rowID);
        db.close();
        db.notifyAll();
    }catch(NumberFormatException e){
        Log.e("INPUT ERROR","Input is not a number!",e);
        //notify the user that the input is invalid.
        Toast.makeText(this,"Invalid Value!",Toast.LENGTH_LONG).show();
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.delete, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}
}

This is the logcat error that I am getting

object not locked by thread before notifyAll()