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array not being filled

This should have at least 3 entries in the array when I view it at a later stage, but it only displays one. I believe this is thee problematic method, any advice?
String[] getKidsNamebyCid(int cid) {
String[] out = new String[20];
try {
String qry = "SELECT KIDSNAME FROM TBLKIDS WHERE CID = ?";//setting query command
ps = connect.prepareStatement(qry);//preparing statement
ps.setInt(1, cid);//setting CID
ps.executeQuery();//running command
int i = 0;
while (ps.getResultSet().next()) {
out[i] = ps.getResultSet().getString("KIDSNAME");
i++;
}
} catch (SQLException se) {
se.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
return out;
}

The getResultSet() call isn't a getter. That method does things to the DB, and you can't just repeatedly call it; the first time you get a ResultSet object (which you need to close), the second time everything is reset. So don't; you need to call getResultSet() once.
How do I know? By reading. Straight from getResultSet() documentation:
This method should be called only once per result.
Also this code is littered with severe code issues more generally focussed around resources. Resources are objects which aren't -just- a bunch of bits in memory, they represent (and hold open) a 'resource'. In the case of DBs, it's connections to the DB engine. You can't just make resources, you have to always put them in 'guarding' blocks that guarantee the resources are cleaned up. As a consequence, you never want them to be a field unless there's no other way (and then the thing they are a field inside of becomes a resource).
So, the fact that your PreparedStatement is a field? No good. The fact that you call .getResource just like that, unguarded? No good.
Finally, your exception handling is silly. The default act when facing checked exceptions is to just add them to your throws clause. If you can't do that, the right move is throw new RuntimeException("uncaught", e);, not what you did.
executeQuery already returns a resultset. Generally, never call getResultSet*.
Finally, arrays are more or less obsolete; you want collections.
Putting it all together:
// delete your 'ps' field!
List<String> getKidsNamebyCid(int cid) throws SQLException {
var out = new ArrayList<String>();
String qry = "SELECT KIDSNAME FROM TBLKIDS WHERE CID = ?";
try (PreparedStatement ps = connect.prepareStatement(qry)) {
ps.setInt(1, cid);
try (ResultSet rs = ps.executeQuery()) {
while (rs.next()) out.add(rs.getString("KIDSNAME"));
}
}
return out;
}
*) The PreparedStatement API is extremely unfortunate. The way you interact with a PS is wildly different vs. a Statement (which you should rarely use; you can't add user input to a plain jane Statement), and yet because reasons and history PreparedStatement extends Statement. That means a whole bevy of methods are in PreparedStatements that you should never call. That's unfortunate. There are 2 things to learn here: [1] Java does not break backwards compatibility, even if that means some of the APIs are horrible, and [2] JDBC is not really meant for 'human consumption'. We don't program our CPUs in machine code either, yet machine code exists and will continue to. We use 'machine code' as glue; something library and language developers use as common tongue. So it is with JDBC: It's not meant for you. Use a library with a nice API, like JDBI. This probably goes beyond what your high school curriculum wants, but hey. There's not much to say except: It's on your curriculum and teacher that they're making you work with outmoded tools 'real'** developers don't use.
**) 'real' in the sense of: Is writing code that powers apps that get a lot of dollars and/or eyeballs.

You need to learn how PreparedStatement actually works. I highly recommend you follow a tutorial to learn how to use it, then follow the pattern for your own code.
But it's also all in the documentation, so let be quote the various relevant pieces.
The javadoc of executeQuery() says:
Executes the SQL query in this PreparedStatement object and returns the ResultSet object generated by the query.
The code in the question is already wrong at this point, since it **ignores the return value of the executeQuery() call.
In addition, the javadoc of getResultSet() says:
Retrieves the current result as a ResultSet object. This method should be called only once per result.
The code in the question is even more wrong at this point, since it calls getResultSet() repeatedly in a loop.
If you had read the javadoc of the methods you're using, it would have been obvious that something is wrong. As already stated, going through a tutorial would have shown how to do this right. Actually, any web search for examples of executing a query using JDBC would show that.
For extra background information for how it works, the javadoc of execute() says:
Executes the SQL statement in this PreparedStatement object, which may be any kind of SQL statement. Some prepared statements return multiple results; the execute method handles these complex statements as well as the simpler form of statements handled by the methods executeQuery and executeUpdate.
The execute method returns a boolean to indicate the form of the first result. You must call either the method getResultSet or getUpdateCount to retrieve the result; you must call getMoreResults to move to any subsequent result(s).
The javadoc of getMoreResults() says:
Moves to this Statement object's next result, returns true if it is a ResultSet object, and implicitly closes any current ResultSet object(s) obtained with the method getResultSet.
The "return multiple results" is not talking about multiple rows from a single query, but about multiple results from multiple queries. It generally requires the execution of a stored procedure, or a block of SQL code, for this to happen.
This is how to correctly get the multiple rows from the execution of a single SELECT statement:
String qry = "SELECT KIDSNAME FROM TBLKIDS WHERE CID = ?";
try (PreparedStatement ps = connect.prepareStatement(qry)) {
ps.setInt(1, cid);//setting CID
try (ResultSet rs = ps.executeQuery()) {
int i = 0;
while (rs.next()) {
out[i] = rs.getString("KIDSNAME");
i++;
}
}
}
If the SQL code in question had returned multiple result sets, you would do it this way:
try (PreparedStatement ps = connect.prepareStatement(qry)) {
// call ps.setXxx() methods here
boolean isResultSet = ps.execute();
while (isResultSet) {
try (ResultSet rs = ps.getResultSet()) {
int i = 0;
while (rs.next()) {
// call rs.getXxx() methods here
i++;
}
}
isResultSet = ps.getMoreResults();
}
}
That is better written using for loops, to keep the loop logic together:
try (PreparedStatement ps = connect.prepareStatement(qry)) {
// call ps.setXxx() methods here
for (boolean isResultSet = ps.execute(); isResultSet; isResultSet = ps.getMoreResults()) {
try (ResultSet rs = ps.getResultSet()) {
for (int i = 0; rs.next(); i++) {
// call rs.getXxx() methods here
}
}
}
}

UPDATE PreparedStatement not updating MSSQL using JDBC

I am trying to update a MSSQL instance using JDBC using a prepared statement, I made a method to update any record in the table when given the column name, the value to update, and the updated value.
public void updateProjectOptions(int projectID, int number, String column){
try {
PreparedStatement ps = conn.prepareStatement("UPDATE cryptic.dbo.projects SET ? = ? WHERE project_id = ?");
int newNum = number+1;
System.out.println(projectID+" "+newNum+" "+column);
ps.setString(1, column);
ps.setInt(2, newNum);
ps.setInt(3, projectID);
int debug = ps.executeUpdate();
System.out.println("Rows affected: "+debug);
} catch (SQLException ex) {
Logger.getLogger(DAL.class.getName()).log(Level.SEVERE, null, ex);
}
}
The first print statement is printing out the correct values so I know the inputs are correct, and the second print statement is letting me know that 1 row is affected which is correct.
If I run the script inside of Management Studio the script runs fine and updates the table, but if I run the script from the java project nothing is updated and no errors are generated.
The db table in question has 4 columns: (int)project_id, (nvarchar)project_name, (int)num_bugs, (int)num_features
Can anyone help me out with getting this to work and/or spot whats wrong?

You can't bind a column name that way, only variables.
I would recommend that you close that PreparedStatement in method scope in a finally block. Your way is asking for trouble.
I would also call writing to System.out a very bad idea. I'd prefer returning the number of affected rows to the user.

Column names cannot be parameterized in prepared statements. You can parameterize only literal values like strings or numbers.

Use of getters in ResultSets

I am trying to write java code to access a table 'customer' with columns 'customer_id', 'email', 'deliverable', and 'create_date'
I have
Connection conn = DriverManager.getConnection(connectionUrl, connectionUser, connectionPassword);
Statement constat = conn.createStatement();
String query = "SELECT * FROM customer WHERE customer_id LIKE " + customerId;
ResultSet rtn = constat.executeQuery(query);
Customer cust = new Customer(rtn.getInt("customer_id"), rtn.getString("email"), rtn.getInt("deliverable"), rtn.getString("create_date"));
conn.close();
return cust;
I am receiving the error:
java.sql.SQLException: Before start of result set
As far as I can tell, my error is in the line where I am creating a new Customer object, but I cannot figure out what I am doing wrong. Can anyone offer me some help? Thanks!

You must always go to the next row by calling resultSet.next() (and checking it returns true), before accessing the data of the row:
Customer cust = null;
if (rtn.next()) {
cust = new Customer(rtn.getInt("customer_id"),
rtn.getString("email"),
rtn.getInt("deliverable"),
rtn.getString("create_date"));
}
Note that you should also
use prepared statements instead of String concatenation to avoid SQL injection attacks, and have more robust code
close the connections, statements and resultsets in a finally block, or use the try-with-resources construct if using Java 7
Read the JDBC tutorial

You should call ResultSet.first() to move the result to the first position. The result set is a programming convention not to retrieve the whole result of the query and keep in memory. As such, its interface is quite low level and you must explicit select the row via methods like first(), last() or next() (each returns true to check if the requested row index is in the set)

You need to add
rtn.next();
before you use the result set.
Usually this is done as
while (rtn.next()) {
<do something with the row>
}

How to process ResultSet you know has only one record in it

I'm struggling with a homework assignment and am getting hung up on some SQL queries.
My query is interrogating an inventory database for the quantity of some item. The query requests the column with the name quantity_in_stock from the table, given the primary key.
I have initialized some prepared statements. This is the one I'm using here:
stmtFindColumn = Database.getConnection().prepareStatement(String.format("select ? from %s where %s = ?",
INVENTORY_TABLE_NAME, SKU) );
Now a separate method is called. I pass it a static const QTY_IN_STOCK, which is defined as "quantity_in_stock" and the item's SKU number, which is the primary key in the table.
private int getIntegerFromTable(String column, String key) {
int toReturn = 0;
try {
// Complete the prepared statement
stmtFindColumn.setString(1, column);
stmtFindColumn.setString(2, key);
ResultSet result = stmtFindColumn.executeQuery();
toReturn = result.getInt(column);
} catch (SQLException e) {
LOG.error(e.getMessage());
e.printStackTrace();
}
return toReturn;
}
When I run the query I get an sql exception that tells me: Invalid column name quantity_in_stock.
I have tried using a while loop processing result.next() and get the same error. I can't find any examples of how to properly get the results when you know only a single record is being returned.
Help!
EDIT: OK, I've found that part of my problem is I'm not getting a result set, where I should expect one. Any ideas?
UPDATE: I've tested my code, using a garden variety statement and a plain string query instead and it works just fine. So the problem is in my use of the prepared statement. Can someone check if I'm using the ? wildcards correctly? Thanks!

as far as i know, the column name may not be a parameter ...

DarkSquirrel42 is right -- you can't replace the column list of the select using a ? parameter marker. Instead, you can String.format that into place too, for example.
bad:
*select ? from INVENTORY_TABLE_NAME where SKU = ?
good:
select QUANTITY_IN_STOCK from INVENTORY_TABLE_NAME where SKU = ?

Getting the count of rows in a Java resultset

Does anyone know a better way of getting the number of rows in a Java resultset returned from a MySQL database? The resultset returned is not going to be the total number of rows read from the database so I don't think I can use SQL's COUNT aggregate function.
public static int getResultSetRowCount(ResultSet resultSet) {
int size = 0;
try {
resultSet.last();
size = resultSet.getRow();
resultSet.beforeFirst();
}
catch(Exception ex) {
return 0;
}
return size;
}

A better answer is to forget about the number of rows until you've successfully loaded the ResultSet into an object or collection. You can keep the count of the number of rows with either of those options.
It's important to close ResultSets (and all SQL resources like Connection and Statement) in the narrowest method scope possible. That means not passing ResultSet out of the persistence layer. Better to get the number of rows using a Collection size() call.
Stop thinking about databases and start thinking in terms of objects. Java's an object-oriented language.

You can execute
SELECT FOUND_ROWS()
immediately after executing your SELECT statement to find the row count.

If you are using Java 6 you can use the JDBC4ResultSet class which has the getUpdateCount method that returns the number of the lines affected by a SQL Statement even for a Select Statement.
See below the example code:
PreparedStatement ps = con.prepareStatement("select * from any_table ...");
JDBC4ResultSet rs = (JDBC4ResultSet)ps.executeQuery();
int rowNumber = rs.getUpdateCount();
I hope that this help!

You can always use SELECT COUNT() with the same exact conditions, before making the actual SELECT.

Here is my solution to this question (since I mostly want the number of records returned to build an array or something similar): Use a collection such as Vector<T> instead.
public Vector<T> getRecords(){
Vector<T> records = new Vector<T>();
init_conn_and_stmt_and_rs();
try {
rs = stmt.executeQuery("SELECT * FROM `table` WHERE `something` = 0");
while(rs.next()){
// Load the Vector here.
}
} catch (SQLException e) {
e.printStackTrace();
}finally{
close_rs_and_stmt_and_conn();
}
return records;
}
Clean and simple, no? Works for any size record set returned (no need to know the size before hand) and makes all the List methods available.
This has served me well for a time now, but if someone sees a flaw in this, please let me know. Always want to make my practices better, ya know.

You can also use the following way to get the total records in the resultSet:
statement = connect.createStatement();
resultSet = statement.executeQuery(sqlStatement);
resultSet.last();
int count = resultSet.getRow();
System.out.println(count);
count is the total returned rows for your result set. ;)