Help me with this java problem plz

Question

this is my interface:
public interface Lockable
    public void setKey (int key);
    public int lock (int key);
    public int unlock (int key);
    public boolean locked();
}and i implemented it in another program, can someone tell me what's wrong? i keep getting the error "int cannot be dereferenced." thx
public void setKey(int newkey){
       int key = newkey;
   public int lock(int key_lock){
       key = key_lock;
       return key;
   public int unlock(int key_unlock){
       key = key_unlock;
       return key;
   public boolean locked(){
       if (key.lock() == key)
            return true;
       else
            return false;
        }

Answer 1

if (key.lock() == key)key is an int. Ints are primitives, not references, so they don't have methods. A Lockable has a lock() method.