Simple Question

[Ruslan Ivanov]

Hi , i have a simple question on reflection.
Let's say i have a class which has a method aMethod(int) which takes an int as a parameter.
WHen using reflection i'd like to invoke that method. The thing is the invoke method takes Object as an argument to pass to the method. I don't know how do i cast it so that i will send a correct type to my method. I can pass to it an Integer but that is incorrect type i must convert it somehow to an int anyone knows how ?

[Cindy Glass]

Integer has a method intValue
Integer myInt = new Integer(5);
int i = intValue(myInt);

[Ruslan Ivanov]

This definatly won't work when invoking the method using this. The type of argument must be passed as an Object
Take a look at the Method class in reflection package method called invoke.(Object,Object[]);
Thanks for assistance

[Ruslan Ivanov]

also i wouldn't want to use isInstance() or instanceof to check what type of object i am dealing with otherwise it be waist of time for me to use this. Maybe i am not just getting an idea how this works yet.

[Cindy Glass]

Well now I think that I do not understand the question.
What's wrong with overloading the method with a version that takes an object and converts it to call the version using an int?
aMethod(Object in){
if (in instanceof Integer){
aMethod(intValue(in));
}
else whatever
}


[This message has been edited by Cindy Glass (edited February 25, 2001).]

[Ruslan Ivanov]

It's a big problem when you don't know about waht type of object i am dealing with when using reflection. It might come over the networking and i must know what i am dealing with. I get the type of it and everything else. Well i just found out that i don't need to cast it , if i dont' pass a correct argument it will just trow an exception at me at runtime i might have to deal with it then, still it's very incovinient to use instanceof if i got 100's of objects , later on i might extends the program and then what would happen ? I must rewrite some stuff which is not good.

[Ruslan Ivanov]

Cindy , if you are interested what it looks like now and it works, here is the idea what i was after.
I have a textfile which has the methods names and the return type for getters. Now i just create my object. I have the Bill class which has methods like these setters and getters i just use it now though the reflection. It's pretty cool because i don't need to know now anything about the class.

import java.awt.*;
import java.util.*;
import java.lang.reflect.*;
import java.io.*;
import java.awt.event.*;
public class Gui extends Frame {
private java.util.List names;
private java.util.List getters;
private java.util.List setters;
private java.util.List datetype;
private int rows;
private int i;
private TextField l1;
private Class c;
private Object o;
public Gui(Object o) {
super("Sotcks/Bonds");
this.o = o;
setSize(200,200);
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
dispose();
System.exit(0);
}
});
loadData(o);
initGui(o);
}
private void initGui(final Object o) {
setLayout(new FlowLayout());
Panel p;
Label l;
for (i = 0; i < 1;i++) {
p = new Panel();
l = new Label(names.get(i).toString());
try {
c = o.getClass();
final Method method = c.getMethod((String)getters.get(i),null);
Object result = method.invoke(o,null);
l1 = new TextField(result.toString());
l1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
try {
String parameter = (String)datetype.get(0);
String set = (String)setters.get(0);
Class z[] = new Class[]{Class.forName(parameter)};
Method methodSetter = c.getMethod(set,z);
Class paramType = methodSetter.getParameterTypes()[0];
Class constrArgs[] = new Class[]{String.class};
Object argument[] = new Object[]{l1.getText()};
Constructor createObject = paramType.getConstructor(constrArgs);
//System.out.println("Constructor name: " + createObject);
//System.out.println("Method name: " + methodSetter);
Object instObject = createObject.newInstance(argument);
//System.out.println("Object created: " + instObject.getClass());
Object objCreate = methodSetter.invoke(o,argument);
System.out.println(o);
}catch(Exception e1){ System.out.println(e);}
}
});
}catch(NullPointerException e) {
System.out.println(e);
}catch(Exception e) {
e.printStackTrace();
}
p.add(l);
p.add(l1);
add(p);
}
pack();
show();
}
private void loadData(Object o) {
Properties allSettings = new Properties();
try {
FileInputStream sf = new FileInputStream("data.txt");
allSettings.load(sf);
}
catch(FileNotFoundException e) {}
catch(IOException e){}
String className = o.getClass().getName();
names = new ArrayList();
getters = new ArrayList();
setters = new ArrayList();
datetype = new ArrayList();
Enumeration keys = allSettings.keys();
StringTokenizer element;
while(keys.hasMoreElements()) {
String keyString = (String)keys.nextElement();
if(keyString.startsWith(className)) {
names.add(keyString.substring(keyString.indexOf("|") + 1));
element = new StringTokenizer((String)allSettings.get(keyString), "|");
getters.add((String)element.nextElement());
setters.add((String)element.nextElement());
datetype.add((String)element.nextElement());
}
}
rows = names.size();
}
public String toString() {
String result="";
Method method;
try {
for ( int i = 0; i < names.size();i++) {
method = c.getMethod((String)getters.get(i),null);
result+=method.invoke(o,null);
}
}catch(Exception e){}
return result;
}
public static void main(String []args) {
Bill s = new Bill();
s.setDiscount(new Double(10.0D));
s.setMaturityDate(new Date());
s.setDescription("Bill for bank");
new Gui(s);
}
}