Question

以下是我的简化图表实现

import java.util.ArrayList;
import java.util.List;

public class TreeNode<E extends Comparable<E>> {
    private E data;
    private List<TreeNode<E>> children;

    public TreeNode(E value) {
        data = value;
        children = new ArrayList<>();
    }

    public E getData() {
        return data;
    }

    public void setData(E data) {
        this.data = data;
    }

    public List<TreeNode<E>> getChildren() {
        return children;
    }

    public void setChildren(List<TreeNode<E>> children) {
        this.children = children;
    }

}

我正在编写代码来查找有向图中是否连接了2个节点。我收到编译错误

public static boolean findIfPathExists(TreeNode<? extends Comparable<?>> start, TreeNode<? extends Comparable<?>> end) {
    Set<TreeNode<? extends Comparable<?>>> visitedNodes = new HashSet<TreeNode<? extends Comparable<?>>>();
    return findIfPathExists(start, end, visitedNodes);
}

private static boolean findIfPathExists(TreeNode<? extends Comparable<?>> start, TreeNode<? extends Comparable<?>> end,
        Set<TreeNode<? extends Comparable<?>>> visitedNodes) {
    if(start == end) return true;
    visitedNodes.add(start);
    List<TreeNode<? extends Comparable<?>>> children = start.getChildren();
    for (TreeNode<? extends Comparable<?>> child : children) {
        if(visitedNodes.contains(child)) continue;
        if(findIfPathExists(child, end, visitedNodes)) return true;
    }
    return false;
}

我在行start.getchildren

收到错误

 Type mismatch: cannot convert from List<TreeNode<capture #11 -of? extends 
Comparable<?>>> to List<TreeNode<? extends Comparable<?>>>

Answer 1

在方法签名中添加一个类型变量：

public static <T extends Comparable<T>> boolean findIfPathExists(
    TreeNode<T> start, TreeNode<T> end) {

private static <T extends Comparable<T>> boolean findIfPathExists(
    TreeNode<T> start, TreeNode<T> end, Set<TreeNode<T>> visitedNodes) {

然后在T {。}}的任何地方使用? extends Comparable<?>。

Answer 2

如果您想保留通配符，请更改该行从

List<TreeNode<? extends Comparable<?>>> children = start.getChildren()

到

List<? extends TreeNode<? extends Comparable<?>>> children = start.getChildren();

无法在java泛型中将列表转换为列表错误

2 个答案: