Can't invoke method <main>

[Yury]

import java.awt.*;
import java.awt.event.*;
import java.lang.*;
import java.lang.reflect.*;
import javax.swing.*;

// Calling apps

public class Debug extends javax.swing.JFrame
{
public Debug()
{
setTitle("java.lang.reflect.Method.invoke");
setDefaultCloseOperation(javax.swing.JFrame.DISPOSE_ON_CLOSE);
getContentPane().setLayout(new BorderLayout(0,0));
getContentPane().setBackground(new java.awt.Color(211,207,199));
setSize(375,162);
setVisible(false);
}

static public void main(String args[])
{
(new Debug()).setVisible(true);
}

void CallactionPerformed(java.awt.event.ActionEvent event) {
String args[] = {""};
PasswordDialog.main(args);
}


void invokeClass(Class cl)
throws ClassNotFoundException,
NoSuchMethodException,
InvocationTargetException
{
// String args[] = new String[1];
String args[] = {""};

Class array[] = {java.lang.Class.forName("[Ljava.lang.String;")};

java.lang.reflect.Method method = null;
try {
method = cl.getMethod("main", array);
} catch (NullPointerException e) {

} catch (NoSuchMethodException e) {

}

method.setAccessible(true);

try {
Object result = method.invoke(cl, args);
} catch (IllegalAccessException e) {
}
}


void pasteButton_actionPerformed(java.awt.event.ActionEvent event)
{
MyClass mc = new MyClass();
Class cl = mc.getClass();

try {
invokeClass(cl);
}
catch (ClassNotFoundException e) {
}
catch (NoSuchMethodException e) {
}
catch (NoClassDefFoundError e) {
}
catch (InvocationTargetException e) {
e.getTargetException().printStackTrace();
}
}
}

// Called apps

import java.awt.*;

import javax.swing.*;

public class MyClass extends javax.swing.JDialog
{
public MyClass()
{
this((Frame)null);
}

public void setVisible(boolean b)
{
if (b)
setLocation(50, 50);
super.setVisible(b);
}

static public void main(String args[])
{
(new MyClass()).setVisible(true);
}
}

// Runtime error

JDK 1.2

Exception occurred during event dispatching:
java.lang.IllegalArgumentException: argument type mismatch
at java.lang.reflect.Method.invoke(Native Method)
at Debug.invokeClass(Debug.java:304)
at Debug.InvokeactionPerformed(Debug.java:320)

JDK 1.4

java.lang.IllegalArgumentException: argument type mismatch
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)
at Debug.invokeClass(Debug.java:304)
at Debug.InvokeactionPerformed(Debug.java:320)

[dlorde]

You can't get a runtime error with the code you posted because it doesn't even compile - not only is PasswordDialog undefined, but in your MyClass constructor you try to call this((Frame) null); when you don't have a constructor that takes a Frame.

I suspect this line:

Class array[] = {java.lang.Class.forName("[Ljava.lang.String;")};

doesn't help.

If you post the code that actually compiles and produces the runtime error, I might take a bit more interest...

It is better to have an approximate answer to the right question than an exact answer to the wrong one...
J. Tukey

[Yury]

Well,

Here is the compiled code.

Note. If I use

String args[] = new String[1];

instead of

String args[] = {""};

Everything is OK.

[cjard]

Class array[] = {java.lang.Class.forName("[Ljava.lang.String;")};


does this line mean you are attempting to invoke the main() method of a String? does String even have a main() ?

C:\javawork\trash>java java.lang.String
Exception in thread "main" java.lang.NoSuchMethodError: main

[cjard]

please note also, that the following statements are NOT equivalent:

String args[] = new String[1];
String args[] = {""};

the following two equivalences are correct:

String args[] = new String[1];
String args[] = new String[]{null}; 

or

String args[] = {""};

String args[] = new String[1];
args[0] = ""; 

-
from my brief investigations, it appears that the invoke method expects two parameters, the second of which is the arguments
The arguments are an array of type Object[], length of 1, and the value at index 0 must be null

the following codes do not produce an error:

String[] args = new String[1];
String[] args = new String[]{null};
Object[] args = new Object[1];
Object[] args = new Object[]{null};

[Yury]

Thanx a lot.

I knew this, but the problem is:

how can I pass parameters

(like a MyClass.main(args) in attached code,
where String args[] = {"Param1", "Param2",..})

via

method.invoke(class, args)

[Yury]

Dear cjard!

You are not quite right about:

"The arguments are an array of type Object[], length of 1, and the value at index 0 must be null"

To pass parameters to <main> (as well as to any method with parameters String args[]) via Method.invoke is possible as

follows:

MyClass.main(new String args[] {"Param1", "Param2",..})

is equivalent to

method.invoke(new Object[] { new String args[] {"Param1", "Param2",..} })

or more detailed

String CallArgs[] = {"Param1", "Param2",..};
MyClass.main(CallArgs);

is equivalent to

Class ParamType[] = {java.lang.Class.forName("[Ljava.lang.String;")};
java.lang.reflect.Method method = null;
try {
method = MyClass.class.getMethod("main", ParamType);
} catch (NullPointerException e) {};
} catch (NoSuchMethodException e) {};

Object InvokeArgs[] = new Object[] {CallArgs};

try {
Object result = method.invoke(MyClass.class, InvokeArgs);
} catch (IllegalAccessException e) {};

Best regards,

Yury

[cjard]

ok.. just remember not to name your variables witha capital letter at the start (callArgs, invokeArgs.. not CallArgs, InvokeArgs)

[Demonpants Software]

Originally posted by Yury
static public void main(String args[])

Don't you have to write public static void main in that specific order? I've never tried your order, but I've had issues in other areas when mixing up the order of things, like instance variables.

[mikeBarr81]

Originally posted by Demonpants Software
Don't you have to write public static void main in that specific order? I've never tried your order, but I've had issues in other areas when mixing up the order of things, like instance variables.

Nope, static public void main(String[] args) is exactly the same as public static void main(String[] args). What you can't do (in any method) is static void public main(String[] args) as the return type is assumed to be the LAST modifier, so whatever comes after the return type is assumed to be the identifier. Since neither static or public are valid identifiers because they're keywords, that wouldn't be allowed.