Manipulating Objects |
If you are writing a development tool such as a debugger, you must be able to obtain field values. This is a three-step process:The
- Create a
Class
object. Retrieving Class Objects shows you how to do this.- Create a
Field
object by invokinggetField
upon theClass
object. For more information, see Identifying Class Fields.- Invoke one of the
get
methods upon theField
object.Field
class has specialized methods for getting the values of primitive types. For example, thegetInt
method returns the contents as anint
value,getFloat
returns afloat
, and so forth. If an object is stored in the field instead of a primitive, then use theget
method to retrieve the object.The following sample program demonstrates the three steps listed previously. This program gets the value of the
height
field from aRectangle
object. Because theheight
is a primitive type (int
), the object returned by theget
method is a wrapper object (Integer
).In the sample program, the name of the
height
field is known at compile time. However, in a development tool such as a GUI builder, the field name might not be known until run time. To find out what fields belong to a class, you can use the techniques described in Identifying Class Fields.Here is the source code for the sample program:
The output of the sample program verifies the value of theimport java.lang.reflect.*; import java.awt.*; class SampleGet { public static void main(String[] args) { Rectangle r = new Rectangle(100, 325); printHeight(r); } static void printHeight(Rectangle r) { Field heightField; Integer heightValue; Class c = r.getClass(); try { heightField = c.getField("height"); heightValue = (Integer) heightField.get(r); System.out.println("Height: " + heightValue.toString()); } catch (NoSuchFieldException e) { System.out.println(e); } catch (SecurityException e) { System.out.println(e); } catch (IllegalAccessException e) { System.out.println(e); } } }height
field:Height: 325
Manipulating Objects |