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In Java every class extends object class implicitly, how it is done and who does that?

+2 votes
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Every class extends object class implicitly. how it is done and who does that? Is it possible to achieve the same behavior for user defined class without using extends keyword, If so how do we do that?

posted Aug 24, 2015 by anonymous

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+1 vote

How object class is inherited into all the Java class without having extends Keyword. I mean what is the logic for making a class to inherit to all the other classes.

0 votes

I use: Python 2.6 and sqlalchemy 0.6.1

This is what I am trying to do:

 from sqlalchemy.types import (
 Integer,
 String,
 Boolean
 )
 from sqlalchemy.ext.declarative import declarative_base

 Base = declarative_base()

 class SampleMeta(type):
 def __new__(cls, name, bases, attrs):
 attrs.update({ 'id': Column('Id', Integer, primary_key=True),
 'name': Column('Name', String),
 'description': Column('Description', String),
 'is_active': Column('IsActive', Boolean)
 })
 return super(SampleMeta, cls).__new__(cls, name, bases, attrs)

 class Sample(Base):
 __tablename__ = 'Sample'
 __table_args__ = {'useexisting': True}
 __metaclass__ = SampleMeta

 def __init__(self, id, name, description, is_active):
 self.id = id
 self.name = name
 self.description = description
 self.is_active = is_active

 def __repr__(self):
 return "" % (self.id, self.name, self.description, self.isactive)

And the error I am getting is this:

 TypeError: Error when calling the metaclass bases
 metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

Now, if I do the same thing above by using

 class Sample(object)

instead of

 class Sample(Base)

it works absolutely fine.

I need to update the attributes of the class dynamically. So, I will be using dynamic attribute and column names. And I need the above piece code to work in order to be able to get there.

+2 votes

Given string representation of an object and a list of classes. How would you determine what class that object belongs to?

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