Reference object e.g

[cow and dog class in the same package]

//reference of abstract

public class ref
{

public static void main(String[] ar)
{
cow c = new cow();
dog d = new dog();
//reference
animal a;
a=c;
a.makeNoise();
//reference
a=d;
a.makeNoise();
}
}

-----------------------------

//reference of abstract

class cow1 extends animal
{
public void makeNoise() { System.out.println ("cow1\n"); }
public static void main(String[] ar)
{
cow1 c = new cow1();
c.makeNoise();
c.eat();
}

}

public class ref1
{

public static void main(String[] ar)
{
cow1 c = new cow1();
// a is reference
animal a;
a=c;
a.makeNoise();

}

}