overridding in java help me to understand the below code.

its a program of inheritance and overridding i understood the whole code except(that line is written in bold and i have underlined that line .It is in class area ) as i could not figure how is it useful and its not creating an object then what does it mean
class fig
{
int num1;
int num2;
fig(int a, int b)
{
num1= a;
num2= b;
}
int area()
{
System.out.println("area of fig ");
return 0;
}
}
class rect extends fig
{
rect(int a, int b)
{
super(a,b);
}
int area()
{
System.out.println(" area of rect " );
return num1*num2;
}
}
class triangle extends fig
{
triangle(int a,int b)
{
super(a,b);
}
int area()
{
System.out.println( " area of triangle ");
return num1*num2/2;
}
}
class area
{
public static void main(String args [])
{
fig obj= new fig(2,3);
rect obj1 = new rect(4,5);
triangle obj2 = new triangle(7,8);
fig fiig;
fiig = obj;
System.out.println( fiig.area());
fiig = obj1;
System.out.println( fiig.area());
fiig = obj2;
System.out.println( fiig.area());
}
}
//fiig is created in reference sort of something with fig i cant figure out what does fig fiig; means in above lines and how is it useful in program can it be useful in other places..