Question

我有一个编译错误，让我有点难过。它说：

TTTree<K,V>无法在下面标记的代码行中转换为TTTree<K,V> 。

public abstract class TTTree<K extends Comparable<K>, V> {

  public abstract TTTree<K, V> put(K k, V v);

  private static <K extends Comparable<K>, V> TTTree<K, V> leaf(K k, V v) { return null; }

  private static class Leaf<K extends Comparable<K>, V> extends TTTree<K, V> {

    private final K k = null;
    private final V v = null;

    @Override
    public TTTree<K, V> put(K ik, V iv) {
        TTTree<K, V> newLeaf = leaf(ik, iv);
        return node(newLeaf, k, this); // <---- !!!! ERROR !!!!
    }
  };

  private TTTree<K, V> node(TTTree<K, V> l, K k, TTTree<K, V> r) {
    return null;
  }
}

似乎这应该有用，那么为什么编译器不喜欢呢？我该怎么做才能解决错误（我想我可以将所有内容转换为原始类型，但这有点过于激烈）。

PS：示例代码减少到'最低限度'，同时仍然产生错误。

PS2：使用Java 8编译器进行编译。

Answer 1

      a:5:{i:0;s:40:"Cannot retrieve payment method instance.";i:1;s:2785:"#0                    /home/tigerbaygiftsco/public_html/app/code/core/Mage/Payment/Model/Info.php(83):       Mage::throwException('Cannot retrieve...')
      #1 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Sales/Model/Quote/Payment.php(216): Mage_Payment_Model_Info->getMethodInstance()
      #2 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Payment/Block/Info/Container.php(60): Mage_Sales_Model_Quote_Payment->getMethodInstance()
      #3 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Payment/Block/Info/Container.php(45): Mage_Payment_Block_Info_Container->_getInfoBlockName()
      #4 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Core/Block/Abstract.php(238): Mage_Payment_Block_Info_Container->_prepareLayout()
      #5 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Core/Model/Layout.php(430): Mage_Core_Block_Abstract->setLayout(Object(Mage_Core_Model_Layout))
      #6 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Core/Model/Layout.php(446): Mage_Core_Model_Layout->createBlock('checkout/onepag...', 'payment_info')
      #7 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Core/Model/Layout.php(238): Mage_Core_Model_Layout->addBlock('checkout/onepag...', 'payment_info')
      #8 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Core/Model/Layout.php(204): Mage_Core_Model_Layout->_generateBlock(Object(Mage_Core_Model_Layout_Element), Object(Mage_Core_Model_Layout_Element))
      #9 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Core/Model/Layout.php(205): Mage_Core_Model_Layout->generateBlocks(Object(Mage_Core_Model_Layout_Element))
      #10 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Core/Controller/Varien/Action.php(345): Mage_Core_Model_Layout->generateBlocks()
      #11 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Core/Controller/Varien/Action.php(270): Mage_Core_Controller_Varien_Action->generateLayoutBlocks()
      #12 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Checkout/controllers/OnepageController.php(186): Mage_Core_Controller_Varien_Action->loadLayout(false)
      #13 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Core/Controller/Varien/Action.php(420): Mage_Checkout_OnepageController->progressAction()
      #14 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(250): Mage_Core_Controller_Varien_Action->dispatch('progress')
      #15 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Core/Controller/Varien/Front.php(176): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
      #16 /home/tigerbaygiftsco/public_html/app/code/core/Mage/Core/Model/App.php(349): Mage_Core_Controller_Varien_Front->dispatch()
      #17 /home/tigerbaygiftsco/public_html/app/Mage.php(640): Mage_Core_Model_App->run(Array)
      #18 /home/tigerbaygiftsco/public_html/index.php(80): Mage::run('', 'store')
      #19 {main}";s:3:"url";s:27:"/checkout/onepage/progress/";s:11:"script_name";s:10:"/index.php";s:4:"skin";s:7:"default";}

Leaf是一个嵌套的静态类。它对TTTree及其泛型类型一无所知。此外，Leaf :: put方法调用TTTree :: node方法，该方法不是静态的，但属于某个TTTree实例。在调用Leaf :: put时，没有指向您正在调用节点方法的TTTree实例的链接。所以方法TTTree :: node应该是静态的。最后一件事：因为TTTree :: node是静态的，你应该声明与你在Leaf类中使用的相同的类型边界

有人可以解释这个“无法转换”的Java泛型错误吗？

1 个答案: