How to instantiate class from with class.forName()

Stanlepunk

I try to create new class from a class name but I fail. My first state it's find a good class, I manage this part but after I find no possibility to instantiate from the class name. I need to do that because all my methods is used everywhere in my code and I need to find information from those in a single place. I hope my purpose is clear...

When I pass the name find with method Field by method forName() the console return Unhandled exception type ClassNotFoundException

import java.util.Iterator;
import java.lang.reflect.*; 

Target class_a = new Target() ;
Target class_b = new Target() ;
Truc class_c = new Truc() ;

void setup() {
  class_a.is(true);
  class_b.is(false);

  Field [] f = this.getClass().getDeclaredFields();
  println("field num:",f.length);
  for(int i = 0 ; i < f.length ; i++) {
    if(f[i].getType().getName().contains("Target")) {
     println("BRAVO it's a good classes");
     println("class:",f[i].getClass());
     println("name:",f[i].getName());

     // I imagine pass the name here to instantiate the class but that's don't work
     //Class<?> class_type = Class.forName(f[i].getName());
     Class<?> class_type = Class.forName("class_a");
     //Class<?> class_type = Class.forName(f[i].getClass());
     Target t = (Target) class_type.newInstance();


     // here I try to call method of the selected class
     println(t.get_is());
   }
 }
}


class Target{
  boolean is;
  Target() {}
  void is(boolean is) {
   this.is = is;
  }  
  boolean get_is() {
    return is;
  }
}


class Truc{
  Truc() {}
}

Chrisir

Please note that there’s a new forum

Better post there

Stanlepunk

again a new forum :) Ok I post on it. Thx

Chrisir

;-)

GoToLoop

Reflection operations demand a try/catch () {} block in order to handle some possible ReflectiveOperationException: #-o

1. https://Processing.org/reference/try.html
2. https://Docs.Oracle.com/javase/10/docs/api/java/lang/ReflectiveOperationException.html
3. https://Forum.Processing.org/two/discussion/27164/string-to-class-classnotfoundexception#Item_5

Stanlepunk

Thx @GoToLoop I improve my code, but I cannot use the Field.getName()to point on the declared Classes created before. I find to information to do that.

import java.lang.reflect.*; 

Inner in_1;
Inner in_2;

void setup() {
  in_1 = new Inner();
  in_2 = new Inner();
  in_1.is(true);
  in_1.is(false);
  /*
  println(this.getClass().getDeclaredConstructors());
  println(this.getClass().getDeclaredClasses());
  println(this.getClass().getDeclaredMethods());
  println(this.getClass().getDeclaredFields());
  */

  Class<?> appCls = getClass(), innerCls = null;
  try {
    innerCls = Class.forName(appCls.getName() + "$Inner");
  }
  catch (final ClassNotFoundException ex) {
    System.err.println(ex);
  }
  Field [] f = this.getClass().getDeclaredFields();
  println(f);
  for(int i = 0 ; i < f.length ; i++) {
    println(f[i].getType());
    println(innerCls);
    if(f[i].getType() == innerCls) {
      println("LA CLASSE, now the mission is to catch info from declared Classes in_1 and in_2");
      println(f[i].getName());
      // println(f[i].get(innerCls));
    }

  }
}




class Inner {
  boolean is; 
  void is(boolean is) {
    this.is = is;
  }
}

GoToLoop

/**
 * getBoolFromField() (v1.1)
 * GoToLoop (2018/Jun/13)
 *
 * Forum.Processing.org/two/discussion/28053/
 * how-to-instantiate-class-from-with-class-forname#Item_6
 */

Inner in;

void setup() {
  in = new Inner(true);
  //final boolean bool = in.is;
  final boolean bool = readBoolFromField(in, "is");
  println(bool);
  exit();
}

static final boolean readBoolFromField(final Object o, final String f) {
  try {
    return o.getClass().getDeclaredField(f).getBoolean(o);
  }
  catch (final ReflectiveOperationException cause) {
    throw new RuntimeException(cause);
  }
}

class Inner {
  boolean is;

  Inner() {
  }

  Inner(final boolean bool) {
    is(bool);
  }

  Inner is(final boolean bool) {
    is = bool;
    return this;
  }

  @ Override String toString() {
    return "" + is;
  }
}

Stanlepunk

Whaouuu, very intresting way. I try tomorrow to use the Field.getName()to pass at method readBoolFromField(in, "is") so I must transform String to Object ?

Chrisir

I think continued on the new forum

jeremydouglass

here: https://discourse.processing.org/t/how-to-instantiate-class-from-with-class-forname/957/2