[java]Bird cannot be resolved to a type

Bonjour,
mon prg compile pas,il donne une erreur
Exception in thread "main" java.lang.Error: Unresolved compilation problems:
Bird cannot be resolved to a type
Bird cannot be resolved to a type
Bird cannot be resolved to a type

at Mystack.main(Mystack.java:28)

pourtant il accepte la class Car
pourquoi il donne erreur pour la class Bird ?aidez moi svp

import java.util.*; 
public class Mystack  
{ 
  private LinkedList list=new LinkedList(); 
    public void push1(Object o) 
    { 
   list.addFirst(o); 
    } 
     
    public void push2(Object obj) 
    { 
      list.addLast(obj); 
    } 
     
    public Object bottom() 
    { 
     return list.getLast(); 
    } 
     
    public Object pop() 
    { 
     return list.removeFirst(); 
    } 
     
    public static void main(String args []) 
    { 
     Car myCar; 
     Bird myBird; 
     Mystack s=new Mystack(); 
     s.push1 (new Car()); 
     s.push2 (new Bird()); 
     myCar=(Car)s.pop(); 
     System.out.println("The first element in the list:"+myCar); 
     myBird=(Bird)s.bottom(); 
     System.out.println("The last element in the list:"+myBird); 
    } 
} 
class Car 
{ 
 String car1,car2,car3,car4; 
 Car() 
 { 
  car1="Benz"; 
  car2="Toyoto"; 
  car3="Qualis"; 
  car4="Santro"; 
 } 
 class Bird 
 { 
  String bird1,bird2,bird3; 
  Bird() 
  { 
   bird1="parrot"; 
   bird2="duck"; 
   bird3="raven"; 
  } 
 } 
}