Java包如何访问上述文件夹中的类
Java package how to access a class in above folder

这是我的目录的样子：

practice(folder)
    GraphTester.java
    graph(folder)
         Digraph.java
         algorithm(folder)
               TopologicalSort.java

我想使用来自GraphTester.java graph.Digraph和graph.algorithm.TopologicalSort

我尝试的是这样的：

package graph;

public class Digraph
{
    ...
}

package graph;
// package graph.algorithm; <-- also doesn't work

public class TopologicalSort
{
    ...
    private Digraph graph; // doesn't work
}

我的问题是，如何从TopologicalSort.java内部使用Digraph ？

====更新===

我尝试了以下操作，但仍无法正常工作

package graph;
//package graph.algorithm; <-- this also didn't work
import graph.Digraph;

public class TopologicalSort
{
    ...
    private Digraph graph;
}

我更新了上面的目录。 我的意图是将GraphTester.java用作外部类，而不使其与程序包graph和graph.algorithm 。 但是，似乎将其放在文件夹practice会导致此问题。