Request.getParameter("") values: Are they null or ""?

Question

Hello:
I have a web page that links up to a MYSQL database. I use JSP files to process the database queries from an HTML form. However, I am having an issue after moving the code from MYSQL 5.0 and JDK 1.5 to a machine with MYSQL 4.X and JDK 1.4.X
I am enabling user to enter several pieces of search criteria that I, in turn, use to build the SQL syntax statement. And I test to see which HTML fields the user has entered something into so that the SQL only includes those where statements.
I first had the following to process the individual search criteria into SQL where statements:
String tester1 = request.getParameter("tester");
String tester = "";
if (tester1 != "") {
     tester += " tester like \"" + tester1 + "%\"" + " and ";
     } else {
tester += "";
so if the user enter "Tommy in the tester field as a search criterion this part of the SQL would be
tester like Tommy%
Then I build the select statment with only the where statements that the user is interested in (and provided search criteria on):
String syntax = "Select * from database where ";
String array[] = { tester, call_from, call_to, r_no, rec_no, date };
for (int counter=0;counter<array.length;counter++){
          if (array[counter] != "") {
          syntax += array[counter];
int a = 0;
int b = (syntax.length() - 4);
String syntax1 = syntax.substring(a, b);
so the above would create
Select * from database where tester like Tommy%
This worked on the previous machine. However, it no longer works on the machine with the older apis. So I have tried everything to weed out the blank database fields so they are not factored in the query (if they are they return nothing as these fields are required to be entered into the database). I tried this:
String tester1 = request.getParameter("tester");
String tester = "";
if ((tester1 != "") || (tester1 != null)){
     tester += " tester like \"" + tester1 + "%\"" + " and ";
     } else {
tester += "#";
. . . and then . . .
String syntax = "Select * from database where ";
String array[] = { tester, call_from, call_to, r_no, rec_no, date };
for (int counter=0;counter<array.length;counter++){
          if (array[counter] != "#") {
          syntax += array[counter];
int a = 0;
int b = (syntax.length() - 4);
String syntax1 = syntax.substring(a, b);
But no matter what I try the query that gets sent to the database is as follows:
Select * from qa_data where tester like "%" and called_from_1 = "" and call_to = "" and r_no = "" and rec_no = "" and (date >= "" and date <= "")
So I am at a loss. It appears that I am not testing for the correct value that the browser is sending to my JSP file when a user does not enter a value in the field. What other than "" and null are there? I have tested for one or the other and both. I am at a loss now as to what to do. I am only concerned with IE6/7 and Firefox 1.5
I output what the value being sent to the JSP file was and it was something like "The tester value is:". So, basically it isn't anything ("").
Can anyone help me here?

Answer 1

Rule #1 when comparing strings: use the equals() method, rather than == or !=
You only use == when checking for null, or checking to see if it is the same object.
if (tester1 == null || tester1.trim().equals("")){
  // value is null/empty/spaces only
else {
  // a value is present
}