NullPointerException ???

Hi.. I keep getting NullPointerException and can't seem to figure out what is wrong with my code? Anybody have any ideas? Thanks in advance

=-=-= stdout -=-=-=-
Exception in thread "main" java.lang.NullPointerException
        at accountServicesInterface.getAllEntries(accountServicesInterface.java:24)
        at accountServicesInterface.main(accountServicesInterface.java:79)

=-=-= java code -=-=-
package com.bedlam.accountServices.common;

import com.bedlam.accountServices.database.*;
import com.bedlam.accountServices.common.LogWriter;

import java.sql.*;

public class accountServicesInterface {
  private Database db;
  private Table table;
  private String tableName;

  public accountServicesInterface(String tableName) {
    db = new Database();
    Table table = db.getTable(tableName);
    this.tableName = tableName;
  }

  public Row getEntry(String crit) throws SQLException {
    return table.getRow(crit);
  }

  public RowSet getAllEntries(String crit) throws SQLException {
    return table.getRows(crit);
  }

  public int generateRandomID() {
    if (tableName.equals("UserClient"))
      return (int)(Math.random()*15000);
    else
      return (int)(Math.random()*30000+15000);
  }

  public int generateValidatedRandomID() throws SQLException {
    int id = generateRandomID();
    String criteria,field;

    if (tableName.equals("UserClient")) {
      criteria = "USERID="+id;
      field = "USERID";
    } else {
      criteria = "MERCID="+id;
      field = "MERCID";
    }

    boolean isValid = isEntryValid(criteria,field);
    while (!isValid) {
      id = generateRandomID();
      isValid = isEntryValid(criteria,field);
    }
    return id;
  }

  public boolean isEntryValid(String crit, String field) throws SQLException {
    Row row = getEntry(crit);
    String isValid = row.get(field);
    if (isValid.equals(null))
      return false;
    else
      return true;
  }
   
     
  public void insertEntry(Row entryRow) {
    try {
      table.putRow(entryRow);
    } catch(SQLException e) {
      LogWriter.write("accountServicesInterface",
                      "insertEntry",
                      "Exception while inserting new row",
                      e);
    }
  }
     
  public static void main(String args []) {
    accountServicesInterface ac
      = new accountServicesInterface("userClient");
    try {
      RowSet rows = ac.getAllEntries("userid>0");
    } catch(SQLException e) {
      LogWriter.write("accountServicesInterface",
                      "getEntry",
                      "Exception while executing SQL statement",
                      e);
    }
  }
}