Writing the Java Classes

Next, you consider the operations needed in a purchase order system, then you write appropriate Java methods. In a simple system based on the tables defined in the previous section, you need methods for registering customers, stocking parts, entering orders, and so on. You implement these methods in the Java class POManager, as follows:

import java.sql.*;
import java.io.*;
import oracle.jdbc.driver.*;

public class POManager {
  public static void addCustomer (int custNo, String custName,
    String street, String city, String state, String zipCode,
    String phoneNo) throws SQLException {
      String sql = "INSERT INTO Customers VALUES (?,?,?,?,?,?,?)";
      try {
        Connection conn =
          DriverManager.getConnection("jdbc:default:connection:");
        PreparedStatement pstmt = conn.prepareStatement(sql);
        pstmt.setInt(1, custNo);
        pstmt.setString(2, custName);
        pstmt.setString(3, street);
        pstmt.setString(4, city);
        pstmt.setString(5, state);
        pstmt.setString(6, zipCode);
        pstmt.setString(7, phoneNo);
        pstmt.executeUpdate(); 
        pstmt.close();
      } catch (SQLException e) {System.err.println(e.getMessage());}
  }

  public static void addStockItem (int stockNo, String description,
    float price) throws SQLException {
      String sql = "INSERT INTO StockItems VALUES (?,?,?)";
      try {
        Connection conn =
          DriverManager.getConnection("jdbc:default:connection:");
        PreparedStatement pstmt = conn.prepareStatement(sql);
        pstmt.setInt(1, stockNo);
        pstmt.setString(2, description);
        pstmt.setFloat(3, price);
        pstmt.executeUpdate(); 
        pstmt.close();
      } catch (SQLException e) {System.err.println(e.getMessage());}
  }

  public static void enterOrder (int orderNo, int custNo,
    String orderDate, String shipDate, String toStreet,
    String toCity, String toState, String toZipCode)
    throws SQLException {
      String sql = "INSERT INTO Orders VALUES (?,?,?,?,?,?,?,?)";
      try {
        Connection conn =
          DriverManager.getConnection("jdbc:default:connection:");
        PreparedStatement pstmt = conn.prepareStatement(sql);
        pstmt.setInt(1, orderNo);
        pstmt.setInt(2, custNo);
        pstmt.setString(3, orderDate);
        pstmt.setString(4, shipDate);
        pstmt.setString(5, toStreet);
        pstmt.setString(6, toCity);
        pstmt.setString(7, toState);
        pstmt.setString(8, toZipCode);
        pstmt.executeUpdate(); 
        pstmt.close();
      } catch (SQLException e) {System.err.println(e.getMessage());}
  }

  public static void addLineItem (int lineNo, int orderNo,
    int stockNo, int quantity, float discount) throws SQLException {
      String sql = "INSERT INTO LineItems VALUES (?,?,?,?,?)";
      try {
        Connection conn =
          DriverManager.getConnection("jdbc:default:connection:");
        PreparedStatement pstmt = conn.prepareStatement(sql);
        pstmt.setInt(1, lineNo);
        pstmt.setInt(2, orderNo);
        pstmt.setInt(3, stockNo);
        pstmt.setInt(4, quantity);
        pstmt.setFloat(5, discount);
        pstmt.executeUpdate(); 
        pstmt.close();
      } catch (SQLException e) {System.err.println(e.getMessage());}
  }

  public static void totalOrders () throws SQLException {
    String sql = 
      "SELECT O.PONo, ROUND(SUM(S.Price * L.Quantity)) AS TOTAL " +
      "FROM Orders O, LineItems L, StockItems S " +
      "WHERE O.PONo = L.PONo AND L.StockNo = S.StockNo " +
      "GROUP BY O.PONo";
    try {
      Connection conn =
        DriverManager.getConnection("jdbc:default:connection:");
      PreparedStatement pstmt = conn.prepareStatement(sql);
      ResultSet rset = pstmt.executeQuery();
      printResults(rset);
      rset.close();
      pstmt.close();
    } catch (SQLException e) {System.err.println(e.getMessage());}
  }

  static void printResults (ResultSet rset) throws SQLException {
    String buffer = "";
    try {
      ResultSetMetaData meta = rset.getMetaData();
      int cols = meta.getColumnCount(), rows = 0;
      for (int i = 1; i <= cols; i++) {
        int size = meta.getPrecision(i);
        String label = meta.getColumnLabel(i);
        if (label.length() > size) size = label.length();
        while (label.length() < size) label += " ";
        buffer = buffer + label + "  ";
      }
      buffer = buffer + "\n";
      while (rset.next()) {
        rows++;
        for (int i = 1; i <= cols; i++) {
          int size = meta.getPrecision(i);
          String label = meta.getColumnLabel(i);
          String value = rset.getString(i);
          if (label.length() > size) size = label.length();
          while (value.length() < size) value += " ";
          buffer = buffer + value + "  ";
        }
        buffer = buffer + "\n";
      }
      if (rows == 0) buffer = "No data found!\n";
      System.out.println(buffer);
    } catch (SQLException e) {System.err.println(e.getMessage());}
  }

  public static void checkStockItem (int stockNo)
    throws SQLException {
      String sql = "SELECT O.PONo, O.CustNo, L.StockNo, " + 
        "L.LineNo, L.Quantity, L.Discount " +
        "FROM Orders O, LineItems L " +
        "WHERE O.PONo = L.PONo AND L.StockNo = ?";
      try {
        Connection conn =
          DriverManager.getConnection("jdbc:default:connection:");
        PreparedStatement pstmt = conn.prepareStatement(sql);
        pstmt.setInt(1, stockNo);
        ResultSet rset = pstmt.executeQuery();
        printResults(rset);
        rset.close();
        pstmt.close();
      } catch (SQLException e) {System.err.println(e.getMessage());}
  }

  public static void changeQuantity (int newQty, int orderNo,
    int stockNo) throws SQLException {
      String sql = "UPDATE LineItems SET Quantity = ? " +
        "WHERE PONo = ? AND StockNo = ?";
      try {
        Connection conn =
          DriverManager.getConnection("jdbc:default:connection:");
        PreparedStatement pstmt = conn.prepareStatement(sql);
        pstmt.setInt(1, newQty);
        pstmt.setInt(2, orderNo);
        pstmt.setInt(3, stockNo);
        pstmt.executeUpdate(); 
        pstmt.close();
      } catch (SQLException e) {System.err.println(e.getMessage());}
  }

  public static void deleteOrder (int orderNo) throws SQLException {
    String sql = "DELETE FROM LineItems WHERE PONo = ?";
    try {
      Connection conn =
        DriverManager.getConnection("jdbc:default:connection:");
      PreparedStatement pstmt = conn.prepareStatement(sql);
      pstmt.setInt(1, orderNo);
      pstmt.executeUpdate(); 
      sql = "DELETE FROM Orders WHERE PONo = ?";
      pstmt = conn.prepareStatement(sql);
      pstmt.setInt(1, orderNo);
      pstmt.executeUpdate(); 
      pstmt.close();
    } catch (SQLException e) {System.err.println(e.getMessage());}
  }
}

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