Here's how my directory look like:

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

```

I want to use `graph.Digraph` and `graph.algorithm.TopologicalSort` from `GraphTester.java`

What I try is this:

```
package graph;

public class Digraph
{
    ...
}

```

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

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

```

My question is, how can I use `Digraph` from inside `TopologicalSort.java`?

==== Update===

I tried the following, but still not working

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

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

```

I updated how the directory look like above. My intention was to use `GraphTester.java` as an outside class and not make it related to the package `graph` and `graph.algorithm`. But, it seems like putting it under the folder `practice` is causing the problem.