java執行緒實現的三種方式以及靜態代理

Sprinining發表於2021-03-13
Java執行緒

執行緒

  • 一個程式中若開闢多個執行緒，執行緒的執行由排程器控制，先後順序不能人為干預。

  • 實現方式

    1. 繼承 Thread類

      • 呼叫run方法，只有主執行緒一條路

      • 呼叫start方法，主執行緒和子執行緒並行交替執行

      • public class MyThread extends Thread{

    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            System.out.println("xixi");
        }
    }

    public static void main(String[] args) {

        MyThread myThread = new MyThread();
        //myThread.run();只有主執行緒一條路，先xixi後haha
        //開啟執行緒，不一定立刻執行，由cpu排程
        myThread.start();//同時執行，xixi、haha交替

        //main執行緒
        for (int i = 0; i < 20; i++) {
            System.out.println("haha");
        }
    }

}

      • 匯入common-io.jar下載圖片

        import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;
import java.net.URL;

public class MyThread2 extends Thread{

    private String url;
    private String name;

    public MyThread2(String url, String name){
        this.name = name;
        this.url = url;
    }

    @Override
    public void run() {
        WebDownloader webDownloader = new WebDownloader();
        webDownloader.downloader(url, name);
        System.out.println("下載了檔名為" + name);

    }

    public static void main(String[] args) {
        MyThread2 t1 = new MyThread2("https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=3246675119,2528014287&fm=26&gp=0.jpg", "csgo1.jpg");
        MyThread2 t2 = new MyThread2("https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=3246675119,2528014287&fm=26&gp=0.jpg", "csgo2.jpg");
        MyThread2 t3 = new MyThread2("https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=3246675119,2528014287&fm=26&gp=0.jpg", "csgo3.jpg");

        t1.start();
        t2.start();
        t3.start();

    }
}

class WebDownloader{
    public void downloader(String url, String name){
        try {
            FileUtils.copyURLToFile(new URL(url), new File(name));
        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("downloader異常");
        } finally {
        }
    }
}

    2. 實現Runnable介面

      • 推薦使用，避免單繼承侷限性，靈活方便，方便同一個物件被多個執行緒使用

      public class MyThread3 implements Runnable{
    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            System.out.println("xixi");
        }
    }

    public static void main(String[] args) {

        //建立實現runnable介面的類物件
        MyThread3 myThread3 = new MyThread3();
        //建立執行緒物件，通過執行緒物件啟動執行緒，代理
        new Thread(myThread3).start();


        for (int i = 0; i < 20; i++) {
            System.out.println("haha");
        }
    }
}

      • 多執行緒同時操作一個物件

        public class MyThread4 implements Runnable{

    private int ticketNums = 10;

    @Override
    public void run() {
        while (true){
            if(ticketNums <= 0)
                break;

            //模擬延時
            try {
                Thread.sleep(20);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "拿到了第" + ticketNums-- + "張票");
        }
    }

    public static void main(String[] args) {
        MyThread4 myThread4 = new MyThread4();
        new Thread(myThread4, "haha").start();
        new Thread(myThread4, "xixi").start();
        new Thread(myThread4, "hehe").start();

    }

}
//多個執行緒操作同一個資源時，執行緒不安全，資料紊亂
/*
haha拿到了第9張票
xixi拿到了第8張票
hehe拿到了第10張票
hehe拿到了第6張票
xixi拿到了第7張票
haha拿到了第5張票
hehe拿到了第4張票
haha拿到了第4張票
xixi拿到了第4張票
xixi拿到了第2張票
hehe拿到了第3張票
haha拿到了第1張票
 */

    3. 實現Callable介面

      • 可以定義返回值、可以丟擲異常

      • import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.concurrent.*;

public class MyCallable implements Callable<Boolean> {

    private String url;
    private String name;

    public MyCallable(String url, String name){
        this.name = name;
        this.url = url;
    }

    @Override
    public Boolean call() throws Exception {
        WebDownloader webDownloader = new WebDownloader();
        webDownloader.downloader(url, name);
        System.out.println("下載了檔名為" + name);
        return true;
    }

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        MyCallable t1 = new MyCallable("https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=3246675119,2528014287&fm=26&gp=0.jpg", "csgo1.jpg");
        MyCallable t2 = new MyCallable("https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=3246675119,2528014287&fm=26&gp=0.jpg", "csgo2.jpg");
        MyCallable t3 = new MyCallable("https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=3246675119,2528014287&fm=26&gp=0.jpg", "csgo3.jpg");

        //建立執行服務
        ExecutorService ser = Executors.newFixedThreadPool(3);

        //提交執行
        Future<Boolean> r1 = ser.submit(t1);
        Future<Boolean> r2 = ser.submit(t2);
        Future<Boolean> r3 = ser.submit(t3);

        //獲取結果
        boolean rs1 = r1.get();
        boolean rs2 = r2.get();
        boolean rs3 = r3.get();

        //關閉服務
        ser.shutdown();
    }


}

class WebDownloader{
    public void downloader(String url, String name){
        try {
            FileUtils.copyURLToFile(new URL(url), new File(name));
        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("downloader異常");
        } finally {
        }
    }
}

  • 靜態代理

    • 真實物件和代理物件都要實現同一個介面

    • 代理物件要代理真實角色

    • 代理物件可以做很多真實物件做不了的事情

    • 真實物件專注做自己的事情

    • public class StaticProxy {
    public static void main(String[] args) {

        You you = new You();

        //代理真實物件runnable
        new Thread(()-> System.out.println("haha")).start();
        
        //代理真實物件you
        new WeddingCompany(new You()).HappyMarry();

        WeddingCompany weddingCompany = new WeddingCompany(you);
        weddingCompany.HappyMarry();
    }
}

interface Marry{
    void HappyMarry();
}

//真實角色
class You implements Marry{
    @Override
    public void HappyMarry() {
        System.out.println("marry!");
    }
}

//代理角色
class WeddingCompany implements Marry{
    
    private Marry target;

    public WeddingCompany(Marry target){
        this.target = target;
    }

    @Override
    public void HappyMarry() {
        before();
        this.target.HappyMarry();//真實物件
        after();
    }


    public void before() {
        System.out.println("before marry");
    }
    public void after() {
        System.out.println("after marry");
    }
}

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