Casting

How to cast objects from one class to another.

About this technique	Details
Category	Core Programming Techniques> Java
Description	You'll learn about: Casting an Object to an Integer Casting an Object to a String Casting an Object to a Date
	You can run this technique code from: Database: Examples3_Java Form: frmCasting NOTE   First make sure that database is running on your localhost SilverStream Server
Related reading	See the chapter on coding Java for SilverStream applications in the Programmer's Guide

Many SilverStream methods return a Java Object which you must then cast to the appropriate class. This example uses the AgiRowCursor getProperty() method to demonstrate.

Casting an Object to an Integer   

The following code illustrates how to take an Object obtained from a view and cast it to an Integer object. The result is then displayed in another field on the form. As that display field receives the focus, the field's name and class are displayed for informational purposes.

  // Clicked event for the button tbGetInteger that has the 
  // caption "Get Integer" 
  // Get a cursor for the currently-selected row in the view 
  AgiRowCursor cursor = vwCasting.getSelectedRowCursor(); 
   
  // Got a cursor? 
  if (cursor != null) 
  { 
       // Yes, so get the value from the Employee ID column 
       Integer id = (Integer) cursor.getProperty("employeeid"); 
   
       // Display the Employee ID in fldID 
       fldID.setValue(id.intValue()); 
   
       // Set the focus to fldID so that the Control and Class 
       // labels are updated 
       fldID.requestFocus(); 
  } 

Notes about the code

• First, the code finds the currently selected row of the view by calling getSelectedRowCursor().

• After making sure that a row was actually selected, the code retrieves the employeeid by calling getProperty("employeeid") on the cursor that was just obtained. The argument employeeid is the column containing the desired data. The code casts the resulting Object to an Integer object by using (Integer).

• The result is displayed in another field by calling intValue() on the Integer object. This is necessary because fldID.setValue() takes an int, which is a primitive data type.

Casting an Object to a String   

The following code illustrates how to take an Object obtained from a view and cast it to a String object. The String is then displayed in another field on the form. As that display field receives the focus, the field's name and class are displayed for informational purposes.

  // Clicked event for the button tbGetString that has the 
  // caption "Get String" 
  // Get a cursor for the currently-selected row in the view 
  AgiRowCursor cursor = vwCasting.getSelectedRowCursor(); 
   
  // Got a cursor? 
  if (cursor != null) 
  { 
       // Yes, so get the value from the Employee Name column 
       String name = (String) cursor.getProperty("name"); 
   
       // Display the Employee Name in fldName 
       fldName.setText(name); 
   
       // Set the focus to fldName so that the Control and Class 
       // labels are updated 
       fldName.requestFocus(); 
  } 

Notes about the code

• First, the code finds the currently selected row of the view by calling getSelectedRowCursor().

• After making sure that a row was actually selected, the code retrieves the employee's name by calling getProperty("name") on the cursor that was just obtained. The argument name is the column containing the desired data. The code casts the resulting Object to a String object by using (String).

• The result is displayed in another field by calling setText().

Casting an Object to a Date   

The following code illustrates how to take an Object obtained from a view and cast it to a Date object. The date is then displayed in another field on the form. As that display field receives the focus, the field's name and class are displayed for informational purposes.

  // Clicked event for the button tbGetDate that has the 
  // caption "Get Date" 
  // Get a cursor for the currently-selected row in the view 
  AgiRowCursor cursor = vwCasting.getSelectedRowCursor(); 
   
  // Got a cursor? 
  if (cursor != null) 
  { 
       // Yes, so get the value from the Hire Date column 
       java.sql.Date hiredate = (java.sql.Date) 
         cursor.getProperty("hiredate"); 
   
       // Display the Hire Date in fldHireDate 
       fldHireDate.setValue(hiredate); 
   
       // Set the focus to fldHireDate so that the Control and 
       // Class labels are updated 
       fldHireDate.requestFocus(); 
  } 

Notes about the code

• First, the code finds the currently selected row of the view by calling getSelectedRowCursor().

• After making sure that a row was actually selected, the code retrieves the employee's hire date by calling getProperty("hiredate") on the cursor that was just obtained. The argument hiredate is the column containing the desired data. The code casts the resulting Object to a Date object by using (java.sql.Date).

• The result is displayed in another field by calling setValue().