泛型类中带有私有迭代器的奇怪输入错误

Question

I'm implementing a linked list in Java 1.7 and I don't understand this behaviour. The parts of the code that matter are this:

public class LListSent<T> implements Iterable<T>{
  //...
  public T get(int pos) {
      //...
  }
  //...
  private class LListSentIterator {
      private final LListSent list;
      private int currPos;
      private LListSentIterator(LListSent list) {
          this.list = list;
          currPos = 0;
      }
      //...
      @Override
      public T next() {
          return list.get(currPos++); //exception in this line
      }
  }
}

The exception I get is:

incompatible Type: Object cannot be converted to T
  where T is a type-variable:
    T extends Object declared in class LListSent

eve though left.get return a T object. Why does this happen?

Answer 1

Your list variable is of type LListSent which is the raw type (so not parametrized) as such the get method called on this instance will return Object and not T .

Change the type of your variable to LListSent<T> .

Note that this will work because LListSentIterator is an inner class and has access to the type variable T .

A cleaner solution would be to parametrized your LListSentIterator class with a type parameter S and so your list variable would become of type : LListSent<S>