How can I set or get a field in a class whose name is dynamic and stored in a string variable?
public class Test {
public String a1;
public String a2;
public Test(String key) {
this.key = 'found'; <--- error
}
}
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Although there are valid reasons for doing this, if you are trying to do this you are probably doing something very wrong.Tom Hawtin - tackline– Tom Hawtin - tackline2010-01-24 16:24:06 +00:00Commented Jan 24, 2010 at 16:24
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2Your code example is very confusing.Duncan Jones– Duncan Jones2015-03-26 12:22:17 +00:00Commented Mar 26, 2015 at 12:22
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2 Answers
You have to use reflection:
- Use
Class.getField()to get aFieldreference. If it's not public you'll need to callClass.getDeclaredField()instead - Use
AccessibleObject.setAccessibleto gain access to the field if it's not public - Use
Field.set()to set the value, or one of the similarly-named methods if it's a primitive
Here's an example which deals with the simple case of a public field. A nicer alternative would be to use properties, if possible.
import java.lang.reflect.Field;
class DataObject
{
// I don't like public fields; this is *solely*
// to make it easier to demonstrate
public String foo;
}
public class Test
{
public static void main(String[] args)
// Declaring that a method throws Exception is
// likewise usually a bad idea; consider the
// various failure cases carefully
throws Exception
{
Field field = DataObject.class.getField("foo");
DataObject o = new DataObject();
field.set(o, "new value");
System.out.println(o.foo);
}
}
3 Comments
ufk
set() asks me for two parameters, Object and value, why not just value? what's the first parameter ? - Field classField = this.getClass().getField(objField.getName()); classField.set(Object,Value)
Michael Borgwardt
@ufk: The first parameter is the object for which you want to set the field. Note that you got the
Field instance by querying the class - there is nothing that links it to a particular instance of that class.
John
and if it is not a primitive ? In my case it's another class (an array of classes which I want to set/change/allocate)
Class<?> actualClass=actual.getClass();
Field f=actualClass.getDeclaredField("name");
The above code would suffice .
object.class.getField("foo");
Unfortunately the above code didn't work for me , since the class had empty field array.
