Java question

[Josh42]

Hi everybody. I have a java question here. . .

v is a Vector.
the Vector holds Objects that contain a getName() method.
Why does the following line give me a "cannot resolve symbol" error??? How do call a method stored in a Vector? Thank you!

v.elementAt(3).getName();

[qball]

v.elementAt(3).getName();


try:

v.elementAt(3).getClass().getName();

[bobcat]

You need to explicitly cast the Object in the vector. So, if you stored an Object instantiated from class Person, you would cast it w Person.

((Person)v.elementAt(2)).getName();

[qball]

bobcat,


You need to explicitly cast...


How does one accomplish this, if they don't know what object is contained in the vector element? Else, what need getName()?

v.elementAt(index).getName();

Fails, as no getName method exists for an Object object.

http://java.sun.com/products/jdk/1.1/docs/api/java.lang.Object.html

getName() exists for the Class object.

http://java.sun.com/products/jdk/1.1/docs/api/java.lang.Class.html

Thus:

v.elementAt(index).getClass().getName();

This is kinda sorta called: Reflection.

[bobcat]

If you know what Object is stored in the Vector you can explicitly cast it as I stated above. If you don't, and you need to do it on the fly; its reflection as qball has stated.

Here is a template of code that you can use.

Lets say you have many different Objects that have the getAddress() method returning a String of an address.

import java.lang.reflect.Method;
.
.
.
Class c = v.elementAt(index).getClass();

try {

Method m = c.getMethod("getAddress", new Class[] { } );
String s = (String)m.invoke(v.elementAt(index),new Object[] { });

// Do something w s.
}
catch (Exception e) {
}