第9章 Future

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背景介绍：假设有一个执行起来需要花时间的方法，我们就不需要等待执行结果出来了，而获取一张替代的提货单，这个提货单就Future参与者

注：当采用Thread-Per-Message方式里，需要线程操作的方法做同步控制，保证线程操作的数据的正确性

public class FutureMain {public static void main(String[] args) {System.out.println("main BEGIN");        Host host = new Host();        Data2 data1 = host.request(10, 'A');        Data2 data2 = host.request(20, 'B');        Data2 data3 = host.request(30, 'C');        System.out.println("main otherJob BEGIN");        try {            Thread.sleep(2000);        } catch (InterruptedException e) {        }        System.out.println("main otherJob END");        System.out.println("data1 = " + data1.getContent());        System.out.println("data2 = " + data2.getContent());        System.out.println("data3 = " + data3.getContent());        System.out.println("main END");}}interface Data2 {    public abstract String getContent();}class RealData implements Data2 {    private final String content;    public RealData(int count, char c) {        System.out.println("        making RealData(" + count + ", " + c + ") BEGIN");        char[] buffer = new char[count];        for (int i = 0; i < count; i++) {            buffer[i] = c;            try {                Thread.sleep(100);            } catch (InterruptedException e) {            }        }        System.out.println("        making RealData(" + count + ", " + c + ") END");        this.content = new String(buffer);    }    public String getContent() {        return content;    }}class FutureData implements Data2 {    private RealData realdata = null;    private boolean ready = false;    public synchronized void setRealData(RealData realdata) {        if (ready) {                                    return;     // balk        }        this.realdata = realdata;        this.ready = true;        notifyAll();    }    public synchronized String getContent() {        while (!ready) {            try {                wait();            } catch (InterruptedException e) {            }        }        return realdata.getContent();    }}class Host {    public Data2 request(final int count, final char c) {        System.out.println("    request(" + count + ", " + c + ") BEGIN");        // (1) 建立FutureData的实体        final FutureData future = new FutureData();        // (2) 为了建立RealData的实体，启动新的线程    通过Thread-Per-Message方式模拟实现Future        new Thread() {                                                  public void run() {                                             RealData realdata = new RealData(count, c);                future.setRealData(realdata);            }                                                       }.start();                                                  System.out.println("    request(" + count + ", " + c + ") END");        // (3) 取回FutureData实体，作为传回值        return future;    }}

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