class Owner{
	private Dog dog;
	public Dog getdog(){return dog;}
	
	public void setDog(Dog dog){
		this.dog=dog;
	}	
}

class Dog{
	private Owner owner;
	public Owner getOwner(){return owner;
	}
	
	public void setOwner(Owner owner){
		if(this.owner!=null)
		 {this.owner.setDog(null);}
		 	this.owner=owner;
		 	owner.setDog(this);
		 
		 }
	public static void main(String arg[])
		{
			Owner owner1=new Owner();
			Owner owner2=new Owner();
			
			Dog dog1=new Dog();
			
			dog1.setOwner(owner1);
		//	dog2.setOwner(owner2);
		

	}
}