在 java 中将函数作为参数传递

我正在熟悉Android框架和Java，并希望创建一个通用的“NetworkHelper”类，该类将处理大部分网络代码，使我能够从中调用网页。

我按照 developer.android.com 的这篇文章创建了我的网络类：http://developer.android.com/training/basics/network-ops/connecting.html

法典：

package com.example.androidapp;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;

import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.util.Log;



/**
 * @author tuomas
 * This class provides basic helper functions and features for network communication.
 */


public class NetworkHelper 
{
private Context mContext;


public NetworkHelper(Context mContext)
{
    //get context
    this.mContext = mContext;
}


/**
 * Checks if the network connection is available.
 */
public boolean checkConnection()
{
    //checks if the network connection exists and works as should be
    ConnectivityManager connMgr = (ConnectivityManager) mContext.getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();

    if (networkInfo != null && networkInfo.isConnected())
    {
        //network connection works
        Log.v("log", "Network connection works");
        return true;
    }
    else
    {
        //network connection won't work
        Log.v("log", "Network connection won't work");
        return false;
    }

}

public void downloadUrl(String stringUrl)
{
    new DownloadWebpageTask().execute(stringUrl);

}



//actual code to handle download
private class DownloadWebpageTask extends AsyncTask<String, Void, String>
{



    @Override
    protected String doInBackground(String... urls)
    {
        // params comes from the execute() call: params[0] is the url.
        try {
            return downloadUrl(urls[0]);
        } catch (IOException e) {
            return "Unable to retrieve web page. URL may be invalid.";
        }
    }

    // Given a URL, establishes an HttpUrlConnection and retrieves
    // the web page content as a InputStream, which it returns as
    // a string.
    private String downloadUrl(String myurl) throws IOException 
    {
        InputStream is = null;
        // Only display the first 500 characters of the retrieved
        // web page content.
        int len = 500;

        try {
            URL url = new URL(myurl);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(10000 );
            conn.setConnectTimeout(15000);
            conn.setRequestMethod("GET");
            conn.setDoInput(true);
            // Starts the query
            conn.connect();
            int response = conn.getResponseCode();
            Log.d("log", "The response is: " + response);
            is = conn.getInputStream();

            // Convert the InputStream into a string
            String contentAsString = readIt(is, len);
            return contentAsString;

        // Makes sure that the InputStream is closed after the app is
        // finished using it.
        } finally {
            if (is != null) {
                is.close();
            } 
        }
    }

    // Reads an InputStream and converts it to a String.
    public String readIt(InputStream stream, int len) throws IOException, UnsupportedEncodingException 
    {
        Reader reader = null;
        reader = new InputStreamReader(stream, "UTF-8");        
        char[] buffer = new char[len];
        reader.read(buffer);
        return new String(buffer);
    }


    // onPostExecute displays the results of the AsyncTask.
    @Override
    protected void onPostExecute(String result) 
    {
        //textView.setText(result);
        Log.v("log", result);

    }

} 

}

在我的活动类中，我以这种方式使用类：

connHelper = new NetworkHelper(this);

...

if (connHelper.checkConnection())
    {
        //connection ok, download the webpage from provided url
        connHelper.downloadUrl(stringUrl);
    }

我遇到的问题是，我应该以某种方式回调到活动，它应该可以在“downloadUrl（）”函数中定义。例如，当下载完成时，将调用活动中的公共 void “handleWebpage（String data）” 函数，并将加载的字符串作为其参数。

我做了一些谷歌搜索，发现我应该以某种方式使用接口来实现此功能。在查看了几个类似的堆栈溢出问题/答案之后，我没有让它工作，我不确定我是否正确地理解了接口：如何在Java中将方法作为参数传递？老实说，使用匿名类对我来说是新的，我真的不确定我应该在提到的线程中在哪里或如何应用示例代码片段。

所以我的问题是如何将回调函数传递给我的网络类并在下载完成后调用它？接口声明在哪里，实现关键字等等？请注意，我是Java的初学者（虽然有其他编程背景），所以我很感激一个完整的解释:)谢谢！