Java包如何访问上述文件夹中的类

Question

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.

Answer 1

Put import practice.graph.Digraph; under your package declaration in TopologicalSort.java .

Make sure the package declaration for TopologicalSort is package practice.graph.algorithm; , it must match the directory structure.

Answer 2

package statement is used to create a package.

In order to use a package you need to use the import starement under the package statements follow by the name of the package you want to use.

You can also "import inline" packages, just a way to use clases or interfaces without import is to write the full path when you use it.

graph.algorithm.TopologicalSort ts = new graph.algorithm.TopologicalSort();

You can read the documentation here

Answer 3

add import statements.

import practice.graph.Digraph;

import practice.graph.algorithm.TopologicalSort;