package testdb;

 * Title:        testdb
 * Description:  simple hello world db example of a
 *               standalone persistent db application
 *               every time it runs it adds four more rows to sample_table
 *               it does a query and prints the results to standard out
 * Author: Karl Meissner
import java.sql.*;

public class testdb {

    Connection conn;    //our connnection to the db - presist for life of program
                        // we dont want this garbage collected until we are done

    public testdb(String db_file_name_prefix) throws Exception    // note more general exception

        // Load the HSQL Database Engine JDBC driver
        // hsqldb.jar should be in the class path or made part of the current jar

        // connect to the database.   This will load the db files and start the
        // database if it is not alread running.
        // db_file_name_prefix is used to open or create files that hold the state
        // of the db.
        // It can contain directory names relative to the
        // current working directory
        conn = DriverManager.getConnection("jdbc:hsqldb:"
                                           + db_file_name_prefix,   // filenames
                                           "sa",                    // username
                                           "");                     // password

    public void shutdown() throws SQLException {

        conn.close();   // if there are no other open connection
                        // db writes out to files and shuts down
                        // this happens anyway at garbage collection
                        // when program ends

//use for SQL commands CREATE and SELECT
    public synchronized void query(String expression) throws SQLException {

        Statement st = null;
        ResultSet rs = null;

        st = conn.createStatement();            // statement objects can be reused with
                                                // repeated calls to execute but we
                                                // choose to make a new one each time
        rs = st.executeQuery(expression);       // run the query

        // do something with the result set.
        st.close();     // NOTE!! if you close a statement the associated ResultSet is
                        // closed too
                        // so you should copy the contents to some other object.
                        // the result set is invalidated also  if you recycle an Statement
                        // and try to execute some other query before the result set has been
                        // completely examined.

//use for SQL commands DROP and INSERT and UPDATE
    public synchronized void update(String expression) throws SQLException {

        Statement st = null;

        st = conn.createStatement();                // statements

        int i = st.executeUpdate(expression);       // run the query

        if (i == -1) {
            System.out.println("db error : " + expression);

    }    // void update()

    public static void dump(ResultSet rs) throws SQLException {

        // the order of the rows in a cursor
        // are implementation dependent unless you use the SQL ORDER statement
        ResultSetMetaData meta   = rs.getMetaData();
        int               colmax = meta.getColumnCount();
        int               i;
        Object            o       = null;

        // the result set is a cursor into the data.  You can only
        // point to one row at a time
        // assume we are pointing to BEFORE the first row
        // points to next row and returns true
        // or false if there is no next row, which breaks the loop 
        for (;;) {
            for (i = 0; i < colmax; ++i) {
                o = rs.getObject(i + 1);    // Is SQL the first column is indexed
                                            // with 1 not 0
                System.out.print(o.toString() + " ");

            System.out.println(" ");
    }                                       //void dump( ResultSet rs )

    public static void main(String[] args) {

        testdb db = null;

        try {
            db = new testdb("db_file");
        } catch (Exception ex1) {
            ex1.printStackTrace();          // could not start db

            return;                         // bye bye

        try {

            //make an empty table
            // by declaring the id column IDENTITY, the db will automatically
            // generate unique values for new rows- useful for row keys
                "CREATE TABLE sample_table ( id INTEGER IDENTITY, str_col VARCHAR(256), num_col INTEGER)");
        } catch (SQLException ex2) {

            //ex2.printStackTrace();  // second time we run program
            //  should throw execption since table
            // already there
            // this will have no effect on the db

        try {

            // add some rows - will create duplicates if run more then once
            // the id column is automatically generated
                "INSERT INTO sample_table(str_col,num_col) VALUES('Ford', 100)");
                "INSERT INTO sample_table(str_col,num_col) VALUES('Toyota', 200)");
                "INSERT INTO sample_table(str_col,num_col) VALUES('Honda', 300)");
                "INSERT INTO sample_table(str_col,num_col) VALUES('GM', 400)");

            // do a query
            db.query("SELECT * FROM sample_table WHERE num_col < 250");

            // at end of program
        } catch (SQLException ex3) {
    }    // main()
}    // class testdb