我如何获得一个内部类来继承封闭类的泛型?
问题内容:
我正在使用Java 6。
我无法让内部类使用与其包含的类相同的泛型类。目前我有
public class TernarySearchTree < T > {
...
protected class TSTNode < T > {
// index values for accessing relatives array
protected static final int PARENT = 0, LOKID = 1, EQKID = 2, HIKID = 3;
protected char splitchar;
protected TSTNode < T > [] relatives;
private T data;
protected TSTNode(char splitchar, TSTNode < T > parent) {
this.splitchar = splitchar;
relatives = new TSTNode[4];
relatives[PARENT] = parent;
}
}
}
现在我得到警告
类型参数T隐藏了类型T
如果我从内部类中删除类型参数(即<T>
从protected class TSTNode<T>
行中删除),则会在该行上出现编译错误relatives = new TSTNode[4]
。
我怎样才能使一切正确?
问题答案:
您可以:
-
<T>
从TSTNode
(即,使其成为非泛型的)中移除类型参数-仍然可以访问external<T>
。 -
将
<T>
class中的type参数重命名TSTNode
为(say)U
。
[更新]
下面是四种重写代码的方法。它们全部编译。我认为您应该考虑使用的用法EnumMap
(请参见下面的版本4)。
版本1 :在内部类中使用不同名称的type参数。您需要使用列表而不是数组。
public class TernarySearchTree<T> {
protected class TSTNode<U> {
// index values for accessing relatives array:
protected static final int PARENT = 0, LOKID = 1, EQKID = 2, HIKID = 3;
protected char splitchar;
protected List<TSTNode<U>> relatives;
private U data;
protected TSTNode(char splitchar, TSTNode<U> parent) {
this.splitchar = splitchar;
relatives = new ArrayList<TSTNode<U>>();
for (int i = 0; i < HIKID; ++i) { // Allocate 4 slots in relatives
relatives.add(null);
}
relatives.set(PARENT, parent);
}
}
private TSTNode<T> node; // When you use it, pass T as U
public TernarySearchTree() {
node = new TSTNode<T>(',', null); // When you use it, pass T as U
}
}
版本2 :从封闭类继承T
public class TernarySearchTree<T> {
protected class TSTNode {
// index values for accessing relatives array:
protected static final int PARENT = 0, LOKID = 1, EQKID = 2, HIKID = 3;
protected char splitchar;
protected List<TSTNode> relatives;
private T data;
protected TSTNode(char splitchar, TSTNode parent) {
this.splitchar = splitchar;
relatives = new ArrayList<TSTNode>();
for (int i = 0; i < HIKID; ++i) { // Allocate 4 slots in relatives
relatives.add(null);
}
relatives.set(PARENT, parent);
}
}
private TSTNode node;
public TernarySearchTree() {
node = new TSTNode(',', null);
}
}
版本3 :使用地图(而不是列表)
public class TernarySearchTree<T> {
protected class TSTNode {
// index values for accessing relatives array:
protected static final int PARENT = 0, LOKID = 1, EQKID = 2, HIKID = 3;
protected char splitchar;
protected Map<Integer, TSTNode> relatives;
private T data;
protected TSTNode(char splitchar, TSTNode parent) {
this.splitchar = splitchar;
// Create a hash map. No need to pre-allocate!
relatives = new HashMap<Integer, TSTNode>();
relatives.put(PARENT, parent); // set -> put
}
}
private TSTNode node;
public TernarySearchTree() {
node = new TSTNode(',', null);
}
}
}
版本4 :将索引定义为枚举+使用EnunMap(而不是哈希图)
public class TernarySearchTree<T> {
protected static enum Index {
PARENT, LOKID, EQKID, HIKID;
}
protected class TSTNode {
protected char splitchar;
protected EnumMap<Index, TSTNode> relatives;
private T data;
protected TSTNode(char splitchar, TSTNode parent) {
this.splitchar = splitchar;
// Create an EnumMap.
relatives = new EnumMap<Index, TSTNode>(Index.class);
relatives.put(Index.PARENT, parent);
}
}
private TSTNode node;
public TernarySearchTree() {
node = new TSTNode(',', null);
}
}
[更新2] 要记住的一件事:使用EnumMap代替顺序索引