Java:Duplicate local variable area

Bonjour,

public class InterfaceTest  
{ 
 interface Area 
    { 
  final static float pi=3.14F; 
  float compute(float x, float y); 
    } 
    class Rectangle implements Area  
    { 
    public float compute (float x, float y) 
    { 
   return(x*y); 
    } 
    } 
    class Circle implements Area 
    { 
       public float compute(float x, float y) 
       { 
      return (pi*x*x); 
       } 
    } 
    public static void main(String[]args) 
  { 
   Rectangle rect=new Rectangle(); 
   Circle cir=new Circle(); 
   Area area; 
   area=rect; 
   System.out.println("Area of Rectangle="+area.compute(10, 20));//area refers to cir object 
   Area area1; 
   area=cir; 
   System.out.println("Area of Circle="+area.compute(10,0 )); 
 } 
} 

j'ai écris ce prg suivant
pendant la compilation j'ai erreur suivantes
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
Duplicate local variable area
at InterfaceTest.main(InterfaceTest.java:29)

la ligne 29 est
Area area;

j'ai corrigé area par area1

après avoir corrigé,j'ai une autre erreur apparaît
Exception in thread "main" java.lang.Error: Unresolved compilation problems:
No enclosing instance of type InterfaceTest is accessible. Must qualify the allocation with an enclosing instance of type InterfaceTest (e.g. x.new A() where x is an instance of InterfaceTest).
No enclosing instance of type InterfaceTest is accessible. Must qualify the allocation with an enclosing instance of type InterfaceTest (e.g. x.new A() where x is an instance of InterfaceTest).

at InterfaceTest.main(InterfaceTest.java:24)
ligne 24 est
Rectangle rect=new Rectangle();