我正在开发一个基于模板的Java类，它实现了各种树结构（例如标准二叉树，红黑树或B树）。我的想法是像Java Collections中的各种列表一样完成它。这是一个接口类，然后由指定的树扩展。然而，我遇到了一个奇怪的问题：
BSTree.java:12: error: BSTree is not abstract and does not override abstract method search(Comparable) in Tree
public class BSTree<T extends Comparable<T>> extends Tree {
^
BSTree.java:20: error: name clash: add(T#1) in BSTree and add(T#2) in Tree have the same erasure, yet neither overrides the other
public void add(T key) throws NullPointerException {
^
where T#1,T#2 are type-variables:
T#1 extends Comparable<T#1> declared in class BSTree
T#2 extends Comparable<T#2> declared in class Tree
BSTree.java:28: error: method compareTo in interface Comparable<T#2> cannot be applied to given types;
if (key.compareTo(ptr.key) == -1) {
^
required: T#1
found: Comparable
reason: actual argument Comparable cannot be converted to T#1 by method invocation conversion
where T#1,T#2 are type-variables:
T#1 extends Comparable<T#1> declared in class BSTree
T#2 extends Object declared in interface Comparable
BSTree.java:42: error: name clash: remove(T#1) in BSTree and remove(T#2) in Tree have the same erasure, yet neither overrides the other
public void remove(T key) throws NullPointerException, TreeException {
^
where T#1,T#2 are type-variables:
T#1 extends Comparable<T#1> declared in class BSTree
T#2 extends Comparable<T#2> declared in class Tree
BSTree.java:49: error: method compareTo in interface Comparable<T#2> cannot be applied to given types;
if (key.compareTo(ptr.key) == 0) {
^
required: T#1
found: Comparable
reason: actual argument Comparable cannot be converted to T#1 by method invocation conversion
where T#1,T#2 are type-variables:
T#1 extends Comparable<T#1> declared in class BSTree
T#2 extends Object declared in interface Comparable
BSTree.java:81: error: method compareTo in interface Comparable<T#2> cannot be applied to given types;
else if (key.compareTo(ptr.key) < 0) ptr = ptr.left;
^
required: T#1
found: Comparable
reason: actual argument Comparable cannot be converted to T#1 by method invocation conversion
where T#1,T#2 are type-variables:
T#1 extends Comparable<T#1> declared in class BSTree
T#2 extends Object declared in interface Comparable
BSTree.java:89: error: name clash: search(T#1) in BSTree and search(T#2) in Tree have the same erasure, yet neither overrides the other
public Node<T> search(T key) throws NullPointerException, KeyNotStoredException {
^
where T#1,T#2 are type-variables:
T#1 extends Comparable<T#1> declared in class BSTree
T#2 extends Comparable<T#2> declared in class Tree
BSTree.java:94: error: method compareTo in interface Comparable<T#2> cannot be applied to given types;
if (key.compareTo(ptr.key) == 0) return ptr;
^
required: T#1
found: Comparable
reason: actual argument Comparable cannot be converted to T#1 by method invocation conversion
where T#1,T#2 are type-variables:
T#1 extends Comparable<T#1> declared in class BSTree
T#2 extends Object declared in interface Comparable
BSTree.java:95: error: method compareTo in interface Comparable<T#2> cannot be applied to given types;
else if (key.compareTo(ptr.key) < 0) ptr = ptr.left;
^
required: T#1
found: Comparable
reason: actual argument Comparable cannot be converted to T#1 by method invocation conversion
where T#1,T#2 are type-variables:
T#1 extends Comparable<T#1> declared in class BSTree
T#2 extends Object declared in interface Comparable
看起来Java认为该对象属于不同类型......如何解决？
这是我的代码：
Tree.java
class Node<T extends Comparable<T>> {
protected T key;
protected Node parent, left, right;
public Node(T key, Node parent) {
this.key = key;
this.parent = parent;
this.left = null;
this.right = null;
}
}
public abstract class Tree<T extends Comparable<T>> {
protected Node<T> root;
protected Integer nodesCount;
public abstract void add(T key) throws NullPointerException;
public abstract void remove(T key) throws NullPointerException, TreeException;
public abstract Node<T> search(T key) throws NullPointerException, KeyNotStoredException;
}
BSTree.java
public class BSTree<T extends Comparable<T>> extends Tree {
public BSTree() {
root = null;
nodesCount = new Integer(0);
}
@Override
public void add(T key) throws NullPointerException {
if (root == null) root = new Node<T>(key, null);
else {
boolean left = false;
Node ptr = root, parent = ptr.parent;
while (ptr != null) {
parent = ptr;
left = false;
if (key.compareTo(ptr.key) == -1) {
ptr = ptr.left;
left = true;
} else ptr = ptr.right;
}
if (left) parent.left = new Node<T>(key, parent);
else parent.right = new Node<T>(key, parent);
}
nodesCount++;
}
@Override
public void remove(T key) throws NullPointerException, TreeException {
/* implementation */
}
@Override
public Node<T> search(T key) throws NullPointerException, KeyNotStoredException {
/* implementation */
}
}
编辑： 感谢您的建议，我能够将错误数量减少到5.这里它们是： javac -d ../bin * .java
BSTree.java:28: error: method compareTo in interface Comparable<T#2> cannot be applied to given types;
if (key.compareTo(ptr.key) == -1) {
^
required: T#1
found: Comparable
reason: actual argument Comparable cannot be converted to T#1 by method invocation conversion
where T#1,T#2 are type-variables:
T#1 extends Comparable<T#1> declared in class BSTree
T#2 extends Object declared in interface Comparable
BSTree.java:49: error: method compareTo in interface Comparable<T#2> cannot be applied to given types;
if (key.compareTo(ptr.key) == 0) {
^
required: T#1
found: Comparable
reason: actual argument Comparable cannot be converted to T#1 by method invocation conversion
where T#1,T#2 are type-variables:
T#1 extends Comparable<T#1> declared in class BSTree
T#2 extends Object declared in interface Comparable
BSTree.java:81: error: method compareTo in interface Comparable<T#2> cannot be applied to given types;
else if (key.compareTo(ptr.key) < 0) ptr = ptr.left;
^
required: T#1
found: Comparable
reason: actual argument Comparable cannot be converted to T#1 by method invocation conversion
where T#1,T#2 are type-variables:
T#1 extends Comparable<T#1> declared in class BSTree
T#2 extends Object declared in interface Comparable
BSTree.java:94: error: method compareTo in interface Comparable<T#2> cannot be applied to given types;
if (key.compareTo(ptr.key) == 0) return ptr;
^
required: T#1
found: Comparable
reason: actual argument Comparable cannot be converted to T#1 by method invocation conversion
where T#1,T#2 are type-variables:
T#1 extends Comparable<T#1> declared in class BSTree
T#2 extends Object declared in interface Comparable
BSTree.java:95: error: method compareTo in interface Comparable<T#2> cannot be applied to given types;
else if (key.compareTo(ptr.key) < 0) ptr = ptr.left;
^
required: T#1
found: Comparable
reason: actual argument Comparable cannot be converted to T#1 by method invocation conversion
where T#1,T#2 are type-variables:
T#1 extends Comparable<T#1> declared in class BSTree
T#2 extends Object declared in interface Comparable
现在，我的代码中有Node<T>和Tree<T>缺少它。但还有什么问题呢？
答案 0 :(得分：7)
当您在JDK中复制功能时，您应该阅读代码以获得一些想法。
您的代码需要使用Node和Tree泛型。
public class BSTree<T extends Comparable<T>> extends Tree<T> {
和
protected Node<T> parent, left, right;
BTW：当你可以使用原语时，你不应该使用包装器。
protected int nodesCount;
答案 1 :(得分：0)
您在Tree声明中遗漏了BSTree上的通用参数：
public class BSTree<T ...> extends Tree<T>
这意味着add(T)中的BSTree方法不会覆盖Tree中的方法，因为它们没有相同的参数类型。
但是，由于T 作为一个类并不比Object更精确（我们只知道它实现了Comparable 接口），两种方法都与add(Object)具有相同的擦除，可能存在不兼容的类型（在编译器的错误输出中标识为T#1和T#2）。
答案 2 :(得分：0)
尝试：
public class BSTree<T extends Comparable<T>> extends Tree<T> {