Java Database Derby Instance 1

package com.han.ch20.q1;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import com.han.Derby;

public class UpdateStu {
    private static Connection conn;
    private static PreparedStatement ps;
    private static ResultSet rs;
    private static ResultSetMetaData rsmd; // ResultSetMetaData has not the close() method
    public static void main(String[] rgs){
        Derby.loadDriver();// As is said in the class Derby, this action is not necessary with a JRE 1.6 and later.
        try {
            // create database "ch20"
            conn=Derby.createDatabaseAndGetConnection("ch20", "", "");

            // drop the table "tb_emp" if it exists
            if(Derby.isTableExists("tb_emp", conn)){
                ps=conn.prepareStatement("drop table tb_emp");
                ps.execute();
            }

            // create a table "tb_emp" in this database
            ps=conn.prepareStatement("create table tb_emp(id int, name varchar(20), department varchar(20))");
            ps.execute();

            // add elements into the table
            ps=conn.prepareStatement("insert into tb_emp values(?,?,?)");
            ps.setInt(1, 1);
            ps.setString(2, "Jing LI");
            ps.setString(3, "Computer technology");
            ps.executeUpdate();
            ps.setInt(1, 2);
            ps.setString(2, "Hao LI");
            ps.setString(3, "Sales department");
            ps.executeUpdate();
            ps.setInt(1, 3);
            ps.setString(2, "Yuanyuan XIONG");
            ps.setString(3, "Copumter technology");
            ps.executeUpdate();
            ps.setInt(1, 4);
            ps.setString(2, "Mei LIU");
            ps.setString(3, "Sales department");
            ps.executeUpdate();

            // consult the information associated with the department "Sales department"
            ps=conn.prepareStatement("select * from tb_emp where department='Sales department'");
            rs=ps.executeQuery();

            // display the query results on the console
            rsmd=rs.getMetaData();
            int numberOfColumns=rsmd.getColumnCount();
            String[] columnNames=new String[numberOfColumns];
            String[] columnTypeNames=new String[numberOfColumns];
            int[] precisions=new int[numberOfColumns];
            for(int i=0;i<numberOfColumns;i++){
                columnNames[i]=rsmd.getColumnName(i+1);
                columnTypeNames[i]=rsmd.getColumnTypeName(i+1);
                precisions[i]=rsmd.getPrecision(i+1);
                System.out.println(columnNames[i]+" : "
                                    +columnTypeNames[i]+"("
                                    +precisions[i]+")");
            }
            for(int i=0;i<numberOfColumns;i++){
                String columnName=columnNames[i];
                if(columnName.length()>precisions[i]){
                    columnName=columnName.substring(0, precisions[i]);
                }

补充：软件开发 , Java ,