Object fooInstance = Class.forName(fooString).newInstance();

public interface Shape {
  public void draw();
}
public class Triangle implements Shape {
  public void draw() {
    ...
  }
}
public class Square implements Shape {
  public void draw() {
    ...
  }
}
public class Program {
  ArrayList<Shape> shapes = new ArrayList<Shape>();
  public static void main(String args[]) {
    ArrayList<String> names = //load all your strings here
    for(String name:names) {
      //exceptions left out for brevity
      //invoke constructor method is slow
      shapes.add(Class.forName(name).newInstance());
    }
    for(Shape shape:shapes) {
      //since this part invokes the draw method without reflection the speed is normal
      shape.draw();
    }
  }
}

Class.forName(fqcn).getConstructor(...).newInstance(...)