how to call "Class" class as parameter in java

Question

for example I have following method in class BugReportFactory:

public static void addFactoryImpl(Class impl) { }

I want to call this method from another class by following ways:

BugReportFactory.addFactoryImpl(new BugReportFactoryAndroid());

It says that following Argument is not applicable for Class class.

Can anyone tell my mistake?

ONE MORE QUESTION:

private static IBugReportFactory INSTANCE = null; 
public static void addFactoryImpl(Class impl) { 
INSTANCE = (IBugReportFactory)impl; 
}

But it shows errors specifying that you cannot cast class to object?

Guys..you all are correct..Its working. ONE MORE QUESTION: private static IBugReportFactory INSTANCE = null; public static void addFactoryImpl(Class impl) { INSTANCE = (IBugReportFactory)impl; } But it shows errors specifying that you cannot cast — Dr. Yatish Bathla
– Dr. Yatish Bathla, Commented Apr 7, 2014 at 6:43
I cannot change the "IBugReportFactory" to "Class" because my another methods are using this instance and i need instance of this class in that method — Dr. Yatish Bathla
– Dr. Yatish Bathla, Commented Apr 7, 2014 at 6:59

Community · Accepted Answer · 2020-06-20 09:12:55Z

5

Try following, Object class has a getClass() method

BugReportFactory.addFactoryImpl(new BugReportFactoryAndroid().getClass());

Or

BugReportFactory.addFactoryImpl(BugReportFactoryAndroid.class);

Will do the job.

ONE MORE QUESTION:
private static IBugReportFactory INSTANCE = null; 
public static void addFactoryImpl(Class impl) { 
     INSTANCE = (IBugReportFactory)impl; 
}
But it shows errors specifying that you cannot cast

Class is different instance is different. Change your INSTANCE Variable type as Class.

private static Class INSTANCE = null;
public static void addFactoryImpl(Class impl) { 
     INSTANCE = impl; 
}

Class is blue print of an instance. You can't assign an instance to Class reference. Both are two different things.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Apr 7, 2014 at 6:34

Abimaran Kugathasan

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3 Comments

Eyal Schneider Over a year ago

Or simply BugReportFactoryAndroid.class

Abimaran Kugathasan Over a year ago

@EyalSchneider : Was on the way of adding it.

Dr. Yatish Bathla Over a year ago

I cannot change the "IBugReportFactory" to "Class" because my another methods are using this instance and i need instance of this class in that method

Joop Eggen · Accepted Answer · 2014-04-07 06:34:45Z

4

BugReportFactory.addFactoryImpl(BugReportFactoryAndroid.class);

answered Apr 7, 2014 at 6:34

Joop Eggen

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Comments

Pablo Francisco Pérez Hidalgo · Accepted Answer · 2014-04-07 06:35:06Z

1

You have two options:

BugReportFactory.addFactoryImpl(BugReportFactoryAndroid.class);

Or:

BugReportFactory.addFactoryImpl((new BugReportFactoryAndroid()).getClass());

I personally prefer the first one.

answered Apr 7, 2014 at 6:35

Pablo Francisco Pérez Hidalgo

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Comments

Hulk · Accepted Answer · 2014-04-07 06:35:59Z

1

(ObjectInstance).getClass() or (Class Name).class

answered Apr 7, 2014 at 6:35

Hulk

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Comments

Michael Rose · Accepted Answer · 2014-04-07 06:36:53Z

1

The Class is some kind of blueprint for an object. When you call new X(), you create a new object of the class X, which means, you build a new class following the blueprint of X.

In your case, the blueprint is wanted, so you need to put BugReportFactoryAndroid.class

Read more at http://www.programmerinterview.com/index.php/java-questions/difference-between-object-and-class/

edited Apr 7, 2014 at 6:36

Michael Rose

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answered Apr 7, 2014 at 6:34

Mirco

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Comments

Hirak · Accepted Answer · 2014-04-07 06:36:57Z

1

If you want to pass the class in your method, the calling code will be:

BugReportFactory.addFactoryImpl(BugReportFactoryAndroid.class);

If you actually wanted to pass an instance of this class, then your method signature should change to:

public static void addFactoryImpl(Object impl) { }

OR

public static <T> void addFactoryImpl(T impl) { }

answered Apr 7, 2014 at 6:36

Hirak

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Comments

Eyal Schneider · Accepted Answer · 2014-04-07 06:46:16Z

Actually I don't think you want to pass a class of type Class as argument. This is a special class used for reflection purposes.

In the case of the Abstract Factory design pattern, typically you have a common interface describing the factory API, and multiple implementations of this interface:

public interface BugReportFactory {
  public A createA();
  public B createB();
}

public class BugReportFactoryAndroid implements BugReportFactory {..}

public class BugReportFactoryIOS implements BugReportFactory {..}

And the class that invokes the factory methods may look like:

public class Foo {
  private List<BugReportFactory> factories = new ArrayList<BugReportFactory>(); 

  public void addFactoryImpl(BugReportFactory factory) { 
    factories.add(factory);
  }

  public void createAll() {
    for (BugReportFactory f : factories) {
      A a = f.createA(); 
      B b = f.createB();
      ... 
    }
  }
}

Dr. Yatish Bathla · Accepted Answer · 2014-04-07 07:50:49Z

1

Finally I found solution both of my Problem: It is as follow:

private static IBugReportFactory INSTANCE = null;
public static void addFactoryImpl(Class<?> impl) {
    Object factoryImpl = null;
    try {
        factoryImpl = impl.newInstance();
    } catch (InstantiationException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    INSTANCE = (IBugReportFactory) factoryImpl;
}

If you want to call this method, it is like this way:

BugReportFactory.addFactoryImpl(BugReportFactoryAndroid.class);

Thanks Everyone for your support and help.

answered Apr 7, 2014 at 7:50

Dr. Yatish Bathla

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