问题描述

跪求哪位大神讲解一下main方法中new Thread中传入的lambda是什么？

我是个新手，刚刚在树上看到了这个程序，DownUtil中有private的内部类继承了thread类，对于main方法中的thread（）怎么调用的不太懂，求耐心看看，大神能够解答一下；

import java.io.*;
import java.net.*;

public class DownUtil {
private String path;
private String targetFile;
private int threadNum;
private DownThread[] threads;
private int fileSize;

public DownUtil(String path String targetFile int threadNum) {    this.path = path;    this.threadNum = threadNum;    this.targetFile = targetFile;    threads = new DownThread[threadNum];}public void download() throws Exception {    URL url = new URL(path);    HttpURLConnection conn = (HttpURLConnection)url.openConnection();    conn.setConnectTimeout(5 * 1000);    conn.setRequestMethod(""GET"");    conn.setRequestProperty(""Accept""image/gif image/jpeg image/pjpeg image/pjpeg + application/x-shockwave-flash application/xaml+xml + ""application/vnd.ms-xpsdocument application/x-ms-xbap + application/x-ms-application application/vnd.ms-excel + ""application/vnd.ms-powerpoint application/msword */*"");    conn.setRequestProperty(""Aceept-Language""zh-CN"");    conn.setRequestProperty(""Charset""UTF-8"");    conn.setRequestProperty(""Connection""Keep-Alive"");    fileSize = conn.getContentLength();    conn.disconnect();    int currentPartSize = fileSize / threadNum + 1;    RandomAccessFile file = new RandomAccessFile(targetFilerw"");    file.setLength(fileSize);    file.close();    for(int i=0; i<threadNum; i++) {        int startPos = i * currentPartSize;        RandomAccessFile currentPart = new RandomAccessFile(targetFilerw"");        currentPart.seek(startPos);        threads[i] = new DownThread(startPos currentPartSize currentPart);        threads[i].start();    }}public double getCompleteRate() {    int sumSize = 0;    for(int i=0; i<threadNum; i++) {        sumSize += threads[i].length;    }    return sumSize * 1.0 / fileSize;}private class DownThread extends Thread {    private int startPos;    private int currentPartSize;    private RandomAccessFile currentPart;    public int length;    public DownThread(int startPos int currentPartSize RandomAccessFile currentPart) {        this.startPos = startPos;        this.currentPartSize = currentPartSize;        this.currentPart = currentPart;    }    public void run() {        try {            URL url = new URL(path);            HttpURLConnection conn = (HttpURLConnection)url.openConnection();            conn.setConnectTimeout(5 * 1000);            conn.setRequestMethod(""GET"");            conn.setRequestProperty(""Accept""image/gif image/jpeg image/pjpeg image/pjpeg + application/x-shockwave-flash application/xaml+xml + ""application/vnd.ms-xpsdocument application/x-ms-xbap + application/x-ms-application application/vnd.ms-excel + ""application/vnd.ms-powerpoint application/msword */*"");            conn.setRequestProperty(""Accept-Language""zh-CN"");            conn.setRequestProperty(""Charset""UTF-8"");            InputStream inStream = conn.getInputStream();            inStream.skip(this.startPos);            byte[] buffer = new byte[1024];            int hasRead = 0;            while(length < currentPartSize && (hasRead = inStream.read(buffer)) != -1) {                currentPart.write(buffer 0 hasRead);                length += hasRead;            }            currentPart.close();            inStream.close();        } catch (Exception e) {            e.printStackTrace();        }    }   }

}

public class MultiThreadDown {
public static void mian(String[] args) throws Exception {
final DownUtil downUtil = new DownUtil(""http://www.wmpic.me/61188/1458367711_GpOvzHwr.jpg""ios.png"" 4);
downUtil.download();

    new Thread(() -> {        while(downUtil.getCompleteRate() < 1) {            System.out.println(""已完成："" + downUtil.getConpleteRate());            try {                Thread.sleep(1000);            } catch(Exception e) {}            }        }).start();}   

}

解决方案

这是Java8中的Lambda表达式相当于实现了一个Runneable接口的内部类通过Thread的start来调用这个内部类.