Storing Class in Array

Question

I have n class (Class1, Class2, .., Classn), each have a static main methods.

I wish to store this class in an array, and call the main method once for each class. But what is the type that I have to declare for this array?

This is what I have done finally according to the reply from T.J. Crowder

ArrayList<Class> meoa = new ArrayList(
                    Arrays.asList(Class.forName("mypackage.Class1"),
                            Class.forName("mypackage.Class2"),
                            Class.forName("mypackage.Class3"),
                            Class.forName("mypackage.Class4"),
                            Class.forName("mypackage.Class5")));    


          for(Class cls:meoa) {
              System.out.println("Invoking:"+cls.getName());
              Method m = cls.getDeclaredMethod("main", String[].class);
              Object[] arg = new Object[1];                  
              arg[0] = new String[] {};
              m.invoke(null, arg);
          }

Rather than calling list of main method, you should chain the functionalists of those methods. — Abimaran Kugathasan
– Abimaran Kugathasan, Commented Mar 10, 2014 at 11:17

T.J. Crowder · Accepted Answer · 2014-03-10 11:24:26Z

4

The type is Class[] (array of Class). (Since main is a static method, we can't really use an interface for this.)

When you're ready to call main, you'd do that via reflection, e.g.:

Class[] classes = /*...create and fill in the array...*/;
for (Class cls : classes) {
    // Look up the main method accepting an array of strings
    Method m = cls.getDeclaredMethod("main", String[].class);
    m.invoke(null, /*...see note below...*/);
}

Re "see note below" above: The argument you pass invoke is an Object[] (array of Object) containing the arguments to give main. Since main expects a single argument (an array of strings), you have to pass it a single-entry Object[] where that one entry is String[]. So for instance, if you were going to pass ["one", "two", "three"] to main, you'd construct the invoke argument like this:

Object[] arg = new Object[1];                    // Room for one argument
arg[0] = new String[] { "one", "two", "three" }; // That one arg is a String array
m.invoke(null, arg);                             // Invoke main

(The null in the call to invoke is for the instance on which to call the method; since main is static, we supply null for that.)

edited Mar 10, 2014 at 11:24

answered Mar 10, 2014 at 11:16

T.J. Crowder

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3 Comments

swapnil7 Over a year ago

@T.J. Crowder any reference?

T.J. Crowder Over a year ago

@swapnil7: Reference for what?

T.J. Crowder Over a year ago

@swapnil7: I linked to Class in the JDK reference (the word Class in the above is a link).

Martin Dinov · Accepted Answer · 2014-03-10 11:18:24Z

0

Arrays in Java (and most statically-typed languages) can only store one type at a time. If the classes all extend the same superclass, then you can declare an array that can store all those classes as follows:

SuperClass[] array = new Superclass[];

Alternatively, if you didn't actually mean (Class1, Class2, ..., Classn) but (object1, object2, ..., objectn), where each object is an instance of some class SomeClass, then that's just:

SomeClass[] array = new SomeClass[];

As for calling the main method on each, just loop through said array and call the method.

answered Mar 10, 2014 at 11:18

Martin Dinov

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