自定义一个不重复且有序的集合

public class SetList<T> extends LinkedList<T> {
    @Override  
    public boolean add(T object) { 
         if (size() == 0) {  
             return super.add(object);  
         } else {
             int count = 0;  
             for (T t : this) {  
                 if (t.equals(object)) {  
                     count++;  
                     break;  
                 }  
             }
             if (count == 0) {  
                 return super.add(object);  
             } else {  
                 return false;  
             }   
        }
    }
}