Using Utility-Class Methods

How to write methods in utility classes that you can then call from any other class.

About this technique	Details
Category	Core Programming Techniques> General
Description	You'll learn about: Creating a utility class Calling a method of the utility class
	You can run this technique code from: Database: Examples3_Java Form: frmCallingMethods Object: com.examples.utilityMethods.BOLoanCalculator NOTE   First make sure that database is running on your localhost SilverStream Server
Related reading	See the chapter on Utility classes, JAR files, and JAVA beans in the Programmer's Guide

Creating a utility class   

To create a class whose methods can be called by all classes:

1. From the SilverStream Designer, select Objects in one of the databases.

2. Click the New icon (at the lower part of the Window) and select New Object.

3. Follow each step in the Wizard to create the class you want. That is, you specify which class it extends, which interface(s) it implements, and so on.

4. Once you have created the class, write the methods for the class.

Calling a method of the utility class   

As with all external methods, you must import the BOLoanCalculator class to be able to call its methods. The following code calls the BOLoanCalculator's calculateLoanPayment() to compute the loan payment, given the following information, which is provided by the user:

• Loan amount

• Annual percentage rate (APR)

• Number of payments

    private void handle_btnCalculateNetPay_actionPerformed(ActionEvent 
     evt) 
       { 
      // This example illustrates calling a method in a utility object 
          BOLoanCalculator boLoanCalculator = new BOLoanCalculator(); 
          double dbAmount = fldAmount.getValue(); 
          double dbAPR = fldAPR.getValue(); 
          int iNumberPayments = fldNumberPayments.getValue(); 
          double dbPayment = boLoanCalculator.calculateLoanPayment( 
             dbAmount, dbAPR, iNumberPayments); 
          fldPaymentAmount.setValue(dbPayment); 
       } 
  

Notes about the code

• fldAmount.getValue() gets the user-entered value from the Enter loan amount text field. Similarly, fldAPR.getValue() and fldLength.getValue()get the user-entered APR and number-of-payments values from their respective text fields.

• To compute the amount per payment, call calculateLoanPayment(). This is a BOLoanCalculator method. It returns the payment amount, which you will display in a text field.

• To display the result in the Payment amount text field, call fldPaymentAmount.setValue() and supply the computed result as its parameter.