When overriding equals in Java, why does it not work to use a parameter other than Object?

public class MyClass {
  private int x;
  public MyClass(int n) { x = n; }
  public boolean equals(Object o) { return false; }
  public boolean equals(MyClass mc) { return x == mc.x; }
  public static void main(String[] args) {
    List<MyClass> list = new ArrayList<MyClass>();
    list.add(new MyClass(3));
    System.out.println("Contains 3? " + list.contains(new MyClass(3)));
  }
}

public boolean equals(Object o) {
  if(!(o instanceof MyClass))
    return false;
  MyClass mc = (MyClass)o;
  return x == mc.x;
}

boolean contains(Object o)
    Returns true if this list contains the specified element.

boolean contains(E o)
    Returns true if this list contains the specified element.

private transient Object elementData[];

public boolean contains(Object elem) {
    return indexOf(elem) >= 0;
}

public int indexOf(Object elem) {
    if (elem == null) {
        for (int i = 0; i < size; i++)
            if (elementData[i]==null)
                return i;
    } else {
        for (int i = 0; i < size; i++)
            if (elem.equals(elementData[i]))
                return i;
    }
    return -1;
}

class A{
    public int content;
    A(){
        this(0);
    }
    A(int value){
        content = value;
    }
    public boolean equals(Object obj){
        System.out.println("overriding equals method");
        return this.content == ((A) obj).content;
    }
    public boolean equals(A a){
        System.out.println("overloading equals method");
        return this.content == a.content;
    }
    public static void main(String[] args){
        A x = new A(1);
        A y = new A(2);
        Object z  = new A(1);
        System.out.println(x.equals(y));
        System.out.println(x.equals(x));
        System.out.println(x.equals(z));
        //override as z is declared as Object at compile time
        //so it will use methods in class Object instead of class A
        System.out.println(x.equals((Object) y));
        System.out.println(x.equals((Object) x));
    }
}
//rant: they didn't teach me these in javaschool and I had to learn it the hard way.