将Object []数组转换为Java中的泛型类型数组时出现ClassCastException

Question

嗨,我是Java的新手,在这段代码中,我想我不是在Main中正确创建Bag？请帮忙谢谢!

线程"main"中的异常java.lang.ClassCastException:[Ljava.lang.Object; 无法转换为[Ljava.lang.Comparable; atBag.(Bag.java:12)mid.Bag.main(Bag.java:91)

        public class Bag<T extends Comparable<T>> implements Iterable<T> {
      private int MAX_ITEMS = 10; // initial array size
      private int size;
      private T[] data;

      public Bag( ) {
        data = (T []) new Object[MAX_ITEMS];
        size = 0;
      }

      public void add(T newItem) {
        // check if it's full, then extend (array resizing)
        if (size == data.length) {
          T[ ] temp = (T [ ] ) new Object[data.length*2];
          for (int i = 0; i < size; ++i)
            temp[i] = data[i];
          // reassign data to point to temp
          data = temp;
        }
        // then do the assignment
        data[size++] = newItem; // assign newItem in the next-available slot
      }

public Iterator<T> iterator() {
    return new BagIterator();
  }

 /***************************
  * nested class BagIterator
  ***************************/
   class BagIterator implements Iterator<T> {
    // instance member
    private int index;

    // (0) constructor
    public BagIterator() {
      index = 0;
    }
    // (1)
    public boolean hasNext() {
      return (index < size); // size in the outer Bag<E>
    }
    // (2)
    public T next() {
      /*
      T temp = data[index]; // save the element value
      index++; // increment index
      return temp;
      */
      return data[index++];
    }
      public static void main(String[ ] args) {
          Bag<String> bag1=new Bag<String>();

          bag1.add("good");
          bag1.add("fortune");
          bag1.add("billionarie");
          for (String x: bag1)
              System.out.println(x);

      }

Answer 1

是的,你正在创建一个Object[]然后尝试将其T[]转换为,由于你对T的约束,编译器将转换为转换为Comparable[](使用原始Comparable类型).

基本上,数组和泛型不能很好地协同工作.

将您的data字段设置为一个Object[]并在必要时转换单个值可能更简单.