Instantiating a class with Reflection

Question

class Start
{
  public static void main( String[] argv ) 
  {
      int argc =argv.length;
      if ( argc == 0 ) {
          System.err.println( "error");
          return;
      }

      try 
      { 
          Class<?> c = Class.forName( argv[argv.length-1] );
          //c kowalski = c.newInstance( );   
      }
      catch ( Exception e ) { System.out.println(e) ; return; }
    }
}
class Test implements InfoInterface
{
    public void display()
    {
        System.out.println("HI!");      
    }
    static int w;
    public int dodawanie (int a, int b)
    {
        w=a+b;
        return w;
    }
}

My problem is how can I create the object of Test class in Start class?
The Test class has to be added by command line.
In this program I have to get methods from Test class via object in Start class.

It's not exactly clear what you want. If you want the names of the methods, you can get them from the `Class` object you refer to as `c`. Or do you want to actually *invoke* the methods? — RealSkeptic, Dec 21 '14 at 15:07
possible duplicate of [Create new class from a Variable in Java](http://stackoverflow.com/questions/1268817/create-new-class-from-a-variable-in-java) — Joe, Jan 01 '15 at 06:41

score 2 · Answer 1 · answered Dec 21 '14 at 15:05

2

You can create dynamic object by just passing the name of the class with complete class path in the argument while executing the program from command line.

answered Dec 21 '14 at 15:05

Bhavik Ambani

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Maarten Bodewes · Answer 2 · 2014-12-21T15:37:50.420

You can get a new class instance by performing:

Class<?> c = Class.forName(argv[argv.length-1]);
Test t = (Test) c.newInstance( );

or, if you have more InfoInterface implementations:

Class<?> c = Class.forName(argv[argv.length-1]);
if (!InfoInterface.class.isAssignableFrom(c)) {
    throw new Exception("Invalid interface specified");
}
Class<InfoInterface> iic = (Class<InfoInterface>) c;
InfoInterface ii = iic.newInstance();

Beware that you specify the full class name (including package name) in the argument used inside of your

Class<?> c = Class.forName(argv[argv.length-1]);

line. You can of course also add the package string yourself:

String command = argv[argv.length-1];
Package p = InfoInterface.class.getPackage();
if (p != null) {
    command = p.getName() + "." + command;
}
Class<?> c = Class.forName(command);

assuming that the Test and other commands are in the same package as InfoInterface.

PS creating some kind of register containing all commands may be more prudent. — Maarten Bodewes, Dec 21 '14 at 15:25

Instantiating a class with Reflection

2 Answers2