reflection static method argument string

Question

public class Star{  
    public static ArrayList initdata(String pattern) {
        ArrayList data = new ArrayList();
            if (pattern != "") {
                ModelCollection mc = Star.find(pattern, 0);
                Iterator dataIterator = mc.iterator();
                    while (dataIterator.hasNext()) {
                        Star star = (Star) dataIterator.next();
                        data.add(star.getName());
                        Debug.trace("StarName" + star.getName());
                    }
            }
        Collections.sort(data);
        return data;
    }
}

I want to invoke method initdata using reflection, I tried to write something like this , but it does not work:

Class c = Class.forName("com.cubiware.fyretv.application.model.Star");
par[0] = String.class;
Method mthd = c.getMethod("initdata", par);        
ArrayList output = (ArrayList) mthd.invoke(null, null);

Answer 1

First, Your check seems weird to me: try if (pattern != null) instead of if (pattern != "").

Why don't you pass the par array, you have illegal argument exception I think. try passing arguments array.

Object[] args = {"someString / maybe null"};
ArrayList output = (ArrayList) mthd.invoke(null, args);

Answer 2

try

ArrayList output = (ArrayList) mthd.invoke(null, (String)null);

It's not good idea to pass null, when method expects Object...

May be this will help

Calling Java varargs method with single null argument?

Answer 3

$ javac -cp dp4j-1.2-SNAPSHOT-jar-with-dependencies.jar -Averbose -All Star.java
Star.java:12:

import com.dp4j.*;

public class Star {

    public Star() {
        super();
    }

    public static ArrayList initdata(String pattern) {
        return null;
    }

    @Reflect()
    public static void main(String[] args) throws java.lang.ClassNotFoundException, java.lang.IllegalAccessException, java.lang.NoSuchMethodException, java.lang.reflect.InvocationTargetException, java.lang.IllegalArgumentException {
        final java.lang.reflect.Method initdataWithStringMethod = Class.forName("Star").getDeclaredMethod("initdata", .java.lang.String.class);
        initdataWithStringMethod.setAccessible(true);
        initdataWithStringMethod.invoke("", new .java.lang.Object[1][]{null});
        final java.lang.reflect.Method printlnWithStringMethod = Class.forName("java.io.PrintStream").getDeclaredMethod("println", .java.lang.String.class);
        printlnWithStringMethod.setAccessible(true);
        printlnWithStringMethod.invoke(System.out, new .java.lang.Object[1][]{"Varargs + reflection? No problem"});
    }
}
    public static void main(String args[]) {
                       ^

$ java Star
Varargs + reflection? No problem

Answer 4

Obviously, your invoke call is similiar to

initdata(null);

Now, inside initdata you do not filter the case where pattern == null which leads us to a call

Star.find(null, 0);

We do not know the implementation of this method - if we're lucky, we get an empty collection. Otherwise, I expect a NullPointerException either in Star.find or later at mc.iterator()