What is the outcome of below code Box class?class Shape

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What is the outcome of below code Box class?

class Shape 
{
	public int area()
        {
		return 1;
	}
}

class Square extends Shape 
{
	public int area()
        {
		return 2;
	}
}

class Rectangle extends Shape 
{
	public int area()
        {
		return 3;
	}
}

public class Box
{
      public static void main(String[] args)
      {
	 Shape obj = new Shape();
	 Square obj0 = new Square();
   	 Rectangle obj1 = new Rectangle();
	 obj1 = (Rectangle)obj0;
	 System.out.println(obj0.area());
      }
}

1. Compilation Error
2. Runtime Error
3. Default Value
4. All of above
5. None of these

Correct Option: A

We cannot assign one child class object to another child class variable.

Box.java:32: error: incompatible types: Square cannot be converted to Rectangle
	 obj1 = (Rectangle)obj0;
	                   ^
1 error